Great video. Bob on. My 200 sq m 100yo 5 bed detached house has original windows with secondary glazing, insulated walls and a peak heat demand of 7kW. Last winter I ran on a 5kW LG which was adequate. The previous year I ran on a 6kW Ecodan which was also ok. This year am trialing a 7kW Vaillant which is probably the right one for the property with a bit of headroom going forward.
Yeah, over-sizing seems like a real issue still, some installers add their own buffer onto the heat loss calc which already has some some over-sizing built in from MCS requirements.
Buffers hold heat and reduce cycling. You should not add it to the calculation for heat loss. Its purely for increasing the amount of energy a single cycle can output and it will continue to distribute into the rads after the ashp is off.
It's ingrained into society that bigger = better - that's the reason - why else do people get 20+kW gas boilers (oh wait that's plumbers) - in fact my in-laws went for a 35kW oil boiler, just in case... I did the calcs on Heatpunk for our 190m2 bungalow - 2001 build, reasonable insulation and newer glazing - it's on the verge of 7ish kW heat loss but that's for varying internal room temps of 15-19C rather than 21C - trying -3C or -5C and it starts to creep towards 8kW as well as tweaking the ventilation rates. So in principle something at 10kW might be useful, but this must be a less common need as you say. Having a full range 4, 6, 8, 10 with the same underlying software and the relevant tweaked hardware to ensure reliability makes more sense to me...though with modulation across those ranges it shouldn't be an issue - I guess the hard bit is that for every drop in C temp the flow temp will tend to increase which then reduces output - there needs to be a clearer "marking" system i.e. Max output at -3C and 50C flow for example...
I did think the same when I heard about this. The thing is Octopus have smart meter data and access to customer addresses so should have a good idea on the heat demand during coldest days of the year before needing to even visit houses. I wouldn't be surprised if the houses they describe as poorly insulated have virtually no energy saving tech and people interested in heat pumps have a skewed view of a typical UK house. I think I heard that the majority were made pre-1920 but as you say I would love to see the data they used to decide that they needed a bigger unit first.
I think its get a little messed up, as pre 1920's houses have more land - in our case we have loads of land based solar + existing oil heating = less than £1000 / year for everything in 2024 (incl running an EV), just fitting a 8kw HP to compliment to oil in winter.
Brilliant analysis. There should be a simple app that: a) knows what the weather is doing at your location b) allows you to record gas consumption in a 24 hour period (reading at start and then 24hrs later, e.g. 7pm-7pm c) What temp you have set inside (and a nudge to keep it at this temp for 24 hours) d) calculate what your heat loss is based on the above e) reminds you to redo the above in all the following months
It is a good idea but there is one imponderable and that is establishing the efficiency of the boiler. I suspect there will be assumptions in the overall calculation.
@@UpsideDownFork There would still be problems with that approach. The gas consumption would have to be that for the coldest days during a 2 week period in winter (the coldest days will probably occur in February). You would have to make sure that your gas consumption was for all rooms being heated to, say, 20C and not the 12C for the room you don't use or the 16C that you like the bedrooms to be at. Under size your heat pump and you could be OK for 11 months of the year but it may not supply enough heat for 1 month of the year. Also there are heat pumps designed to work at lower temperatures (40 to 50C water flow temperatures) which in general need buildings with better insulation and large radiators and heat pumps that can work at 70C flow temperatures. The efficiency of a heat pump varies with temperature difference, a pump with a outside to water flow temperature difference of 40C will be more efficient than one designed to give a 70C difference. A ashp with a cop/scop figure of 1 difference means that the one with the lower cop/scop needs to be rated 25% higher. It has been stated that the average heat loss in UK homes is around 6kW BUT averages don't mean that much when selecting a suitable heat pump, many house would below this figure and many would be above. This puts the 6 and 10Kw Cosy ASHP in the correct ballpark for the range of UK homes.
Good video and I agree with you.The open energy monitor stuff is exciting stuff (if you are into geeking out) and the aggregated data is certainly showing that even amongst the geekiest of the designer and installers the oversizing is evident - and one of the reasons is the lack of true small capacity ASHPs. Of course the conundrum is once you are dropping below 5KW output that is impacting on the regeneration time of the hot water cylinder. Anyone with a gas boiler who is seriously considering an ASHP and is thinking seriously of using the open energy monitoring kit, should give serious thought to buying the open energy monitoring kit now and installing it on their current system - it will do a much more accurate heat loss calculation and enable a better decision to be made on sizing the ASHP.
@ I was thinking about this idea as it applies to me. I have a Viessmann 200 gas boiler running pure weather compensation (no internal room reference) on really low flow temperatures (for a gas boiler) and so it is actually running like a heat pump in winter (running 24/7).
@@normanboyes4983 My Veissman 100 system boiler won't run on a low temp. It cycles hopelessly, doing about 30 seconds on and 5 minutes off indefinitely after an initial 3-4 minute run, unless the temp dial is set to above 65C. I don't know what its algorithm is doing but I suspect it thinks the return temp is too high.
@@xxwookey I know nothing about the Viessman 100 and its performance characteristics. Having said that it does not sound right. How old is the boiler and how long has it been behaving like this?
I agree on my 4 bed house my heatpump sized 8.5 kw Ecodan . On heat pump monitor I never see Higher than 2kw but still see to run in winter. Andrew Scotland
Wholeheartedly agree they should have a COSY 4 Option, Our house 3 bedroom semi detached has a heatloss of just 2.1kw at -3.7c. We had the choice of the Cosy 6 or Daikin Altherma 3 and opted for the Daikin, I cannot see how the cosy would effeciently heat our home in typical mild weather without cycling.
..yes, although a smaller market I guess - our house is quite large (250m2) and oldish (1950s/90s) heat demand is around 12kW on the EPC - even with loads of loft insulation, cavity walls insulation, DG etc. So we have a 12kW Panasonic unit. Not as closely monitored, but as an example -3 outside, 21 inside (overnight heat banking), 2.5kW IN to the heatpump Overspeccing is far better than under-speccing - as if you do that you end up running in "kettle" mode too much of the time, and that kills the benefits
Enjoying your content [and others] while nursing my antique 16-22 Potterton boiler towards the end of its life in my 3 storey 1860s end-of-terrace home. I did do as much internal wall insulation as was feasible over 30yrs ago, it was somewhat 'experimental'. I wonder how the heat loss is estimated on party walls of terraces as you don't know how another home is occupied. My air changes/hr are probably a nightmare as the 3 floor stairwell acts like a chimney drawing heat upwards and cold in from below. Only the inner London heat island as a bonus...
Thanks for commenting! Party walls use assumptions just as the rest of the heat loss calculation does. That's why this blunt instrument is ok, but far from perfect.
I need about 3 or 4kW, years ago I went and found myself a combi-boiler with very deep modulation, 12:1 as I wanted to avoid cycling due to wear and inefficiency.
Nice! Not many heat pumps to choose from in that lower range. Lots of options above 5. HP modulation ratio seems to be fixed somewhat across brands and models, very different to boilers in that respect.
The thing is that Octopus' 3 rate tariff is designed to cause your heat pump to cycle during the day. To use the cheapest priced electricity you need a heatpump that can bring the home up to a high temp quickly during a 3 hour period and then stop for many hours before doing the same again.
That’s not actually realistic cos many houses will cool significantly in cold weather even during the 3 hours of the high price cosy period. More realistic is to do the hot water in cheapest period and then run heating reasonably hard for rest of cheap periods and then run heating at a lower level for the mid price periods. A battery also helps a lot! My pretty well insulated older house would be horrible if only heated in cheapest cosy periods
My 1920 house high celling solid wall double glazed, r 15 recently topped up to r25 open space 3 sides getting a lot of wind , heat loss 22kwh still , in the end I went for a big gas boiler and don’t regret it one bit , this was after 3 different calculations, I just don’t get how the government think over 30% just can’t have heat pumps without over 20K of extra external insulation
@@Biggest-dh1vr I known them well as I'm currently on Agile. But if Octopus is expecting to offer more tariffs that have complex TOU pricing they would also focus on heat pumps that could still operate well, which would mean units not designed to operate all the time.
Completly agree here. Im just doing it my self on a grade EPC F house - a 6kw heat pump (will suffice) - as its the same pump irrespective as to whether you need 4Kw Hl or 8KW HL - its the same heat pump - I'm just keeping oil (as its 50p/l) just to fill those cold spots (albeits for the next few years to see how i get on). Would be great to know what you EPC rating is?
My latest EPC is an E but since then I've spent £6k on insulation materials, heat pump, solar panels, change all bulbs for LED etc. should bump it up a few of their arbitrary categories.
I have a 1952 three-bedroom property; I wouldn't say it is small - you could get a double-bed and change into every bedroom; and it has been insulated. Octopus have proposed to install a 4kW heat pump and that actually seems to be the right size based on some rule-of-thumb calculations I did based on my existing use of gas. So it does seem to me like a 10kW unit would be a monster!
Not all of us are in the South of England. Quick heat pump calculations (based off current oil consumption) and I'm likely needing 8 to 10kW here in the North of Scotland. As long as it modulates down. Occasionally get weeks at -10C. Have seen as low as -29C (back in 2010). 6kW heat pump would likely work in a hybrid system, but you don't get grants for hybrid systems any more. It therefore needs to cope with actual cold, not just average cold. Daikin do one whereby only refrigerant is outside. That or air to air (and no grant) make more sense than most "water outside" heat pumps to many of us.
Your latitude doesn't make a difference to the usual heat loss calculation because usually they target -3 as the low temp. Your heat loss at -3C is the same in scotland as it is in england, its just much more likely to actually happen up in scotland, and way below -3 too. You can have your heat loss calc done for a lower temp outside, but that's not usually the assumption when people are quoting their heat loss figures.
@@jezlawrence720 My "local" site used for MCS heat loss calculations is Dyce (Aberdeen airport). that's relatively sheltered, relatively near the coast, and often a good 5C warmer than places using that as a reference. It's also the coldest mean air temperature of any of the 18 sites mentioned for the UK. Even locally you can get massive differences in temperature due to topology. That -29C I mentioned was just the digital thermometer in my car, but within about 6 miles of Dyce where it was a nice and toasty -11C. Point stands - heat pump needs to be able to handle properly cold for several days, otherwise it can't be the sole source of heating. You have to size it for that.
@@grahamleiper1538you might lose a few degrees in some rooms, but there's a bit of headroom in the output for when the temperature drops below the temperature used for the heat loss calculation.
Design a system for a 45 degree flow and when it gets colder for one or two days a year, you can always ramp the flow up to 50 or 55 and take the hit on efficiency, or you can allow your rooms to drop by 1 to 2 degrees during that time? I take your point that some medium properties will indeed need 10kW. I just don't think that's a majority or even average case.
@@UpsideDownFork looking at the Heat Geek cheat sheet, 10kW would be enough for 150m2 at 65W/m2 (the worst case renovated cavity wall property). Or 90m2 of worst case Victorian or older single glazed.
One of the best economic cases for heatpumps is replacing oil boilers (that also need new oil tanks) on large old remote properties. Agree also wish to see lower powered heatpump or idealy two compressors so much high modulations range.
Really we don't want a Cosy 4 product but an indoor wall mounted unit to replace a gas boiler. We already have A2A internal wall mounted units of 3.6kw so we just need a slightly different shaped A2W unit. There are a load of people living in terraced, townhouse, flats that don't have a suitable outdoor space for a normal unit. Also I think many people in smaller houses would be more likely to consider one of you said it can go in the kitchen larder cupboard where there current gas boiler is. Also the less disruption the lower the install costs would be.
@brackcycle9056 They already exist in A2A form that you might have in a bedroom. So one in a kitchen isn't likely to be much of an issue noise wise. Yes you would have a hole in the wall but you currently have one for your boiler flu so you would just have two rather than the current one you have with a gas boiler.
@@danthep You are thinking of standard split AC units. They also sell units where everything is internal to the building. The only thing outside is an air flow in and exhaust vent.
An installer told me I needed 17kw, and that was after he assumed perfect insulation (which is nowhere even close), more like a barn with the door left open. I am on oil currently for about slightly over 300 m2 1904 property. In previous winters about 1000 liters of oil (or 10,000KWh of fuel) lasts about 2 months, so on average this is not even 1 liter per hour, so way less than their estimate, honestly I reckon 5kw in the background would take care of 90% of it. To the properties credit I did install under floor in ALL of the 300m2 which made a big difference, fortunatly its generally mild on the south coast. However cannot get the install as just does not tick the right boxes…
17?! Wow. I've seen some of these properties where the installer fits 2 units in cadence to accommodate the high heat loss but the second unit only ever ends up doing DHW because the system of 2 pumps is ultimately oversized and unnecessary.
Were a similar sized barn conversion with ok insulation in north wales and we came out with a heat loss of 11.5kw at -2.8. We were using 2500l of oil a year and nearly all underfloor heating. Testing running this on a Samsung 12kw gen6 but leaving oil in for backup and dhw for now and will see how it goes over winter and what the numbers show.
I think its usually a good idea to have a heat source that is significantly higher than the heat losses of the property. If the heat source was sized to match the heat losses then it would take a very long time for the property to reach a comfortable temperature and the source would be running 'flat-out' for extended periods. This may be why Octopus are suggesting that you should select a 10kW heat pump for a larger property even if your heat loss is much less.
The heat loss is designed to calculate the worst case situation, rather than a typical winter's day. My own heat pump runs on minimum output for almost the entire heating season. You can see more of this on heat pump monitor if you want to get into the weeds. There are none on there that are running flat out for extended periods, but in many ways that is better for the compressor than switching off and on all the time.
@@UpsideDownFork The fact that your heat pump is mostly running on minimum output sounds to me like it is sized correctly (or perhaps as you imply, its too big for your property), but this kind of proves my point that you need a heat source which is greater than the heat losses just to get things up to temperature before throttling back. I guess that this is unimportant if the heating is running 24/7 or the property is not subject to rapid changes in outside temperature. Apart from providing space heating, the heat pump also needs to provide additional heat for DHW and to recover the water temperature as quickly as possible. This is another reason why you might need a heat pump with a higher output than you might think.
@@tonydean7543if your heat loss at a sustained -3 degrees is 5kw then the required heat input at +5 degrees will be so much smaller that a 5kw heat pump will easily get things up to temp. In fact, a 5, 7 or 10kw unit won't put any more heat into the building any more quickly. You are limited by weather compensation (flow temp), pipe sizing and emitter sizing. Once you understand the relationship between these factors, you'll start to see that there is almost no case for oversizing a heat pump. The only time you could benefit may be when you have sustained periods far below your design temperature. It just makes no sense to design a heating system for the 0.1% of the year, when we should be designing for the majority of the heating season 👍
Heat pumps have come a long way in terms of capability etc, however my mid 80's warm air gas heating system warms my open plan property quickly. Cavity wall insulation, double glazing and a well insulated loft plus global warming (milder weather) helps to keep the heating costs at a reasonable level. However i might move to a heat pump in the future.
I do like Vaillant's approach. A deep look at the data shows that their variable DT does work quite well. Cycling is inevitable for 95% of the year but short cycling is a different issue that can be avoided with the correct size pump and avoiding zoning.
I'm moving to a well insulated 2 bed detached bungalow, as a single householder. I think a small heat pump would suit me fine. As you say, I'd sooner it work efficiently for 95% of the time even if it struggled in exceptional weather. I wonder if Octopus still fit smaller (4Kw)? heat pumps from other manufacturers, like Daikin? I might try British Gas for my heat pump survey as I'm concerned that Octopus will recommend a Cosy 6.
I agree they should have gone to a cosy 4 over a cosy 6, I've been looking into all this and in my new build house other than the environment effect having a heat pump makes no different for me on my gas bill, the only time I would save money in the long run would be is getting solar and battery's to run all the system as a hole but since I can't afford solar yet 😢 the heat pump will have to wait.
I just had a blower test done on our house and it was way higher than expected. 4 ach. But as my hp has worked well never inputting more than 5kw. I assumed it must be more air tight. The mcs heatloss calculation is covering windy and cold day as the worst case. These are not that common where i am. We have mild windy days and still cold days generally. Hence its rare to get close to the heat that was calculated I suspect.
@@UpsideDownFork quite a few small ones. A particularly bad fireplace. But this is an 1870 terrace house that has had lots of work done but of varying quality. What it made me realise is it is not 4ach all the time it's very dependant on the wind and probably the direction too. I have some room for improvement...
@andrewcunningham1 no this was the ach50. I realise that the normal pressure it's way lower. But I guess what I had not considered was that drafts are just as variable as conductive heat losses. Some day you lose a lot others you lose a little.
@@joewentworth7856 Dividing by 20 brings your ACH down to a good low level. A brand new house is supposed to be about 0.3CH whereas yours is 0.2 ACH..so more airtight than a brand new house!
What we need is better heat loss measurements. Current system: homeowner has no idea. Even the best professional has to guess at some numbers, use guidelines, hope that what he can see represents what is hidden, etc. With this bad data he comes back to the homeowner with a heat loss number and a heat pump recommendation which sounds good, e.g. 9 kW heat loss 10 kW unit. You know looking at the specs that 10 kW unit means maybe 10 kW at some temperature but not every temperature, so the HP chosen only sounds good to the homeowner. Once he says "sure", that's the expensive thing he's stuck with until it wears out, no matter how wrong the professionals he relied on were.
@6:49. I think this one looks artificially worse because the three data points you look at the room temperatures are low (18.5,16.6,17.6). So they would be much higher if the room temperature was set to 20-21°c. But even so the 10kw unit is likely overkill and a 7kw would be the logical choice. It seems somewhat pointless doing a heat loss calculation and then totally ignoring it! 😂
1990’s house is modern really compared with millions of houses built before cavity walls. I wonder if any of those houses with heat pumps have solid walls. I have a gas boiler and it has to be on 8 hours a day when outside temps go below 5 degrees mainly due to the walls which suck heat out.
@ but larger heat pumps will be needed to meet the demand is what I mean. Personal I will get EWI before installing a heat pump but many will not and so will need large unit. I personally think the gov should remove VAT from insulation products to encourage more people to insulate. But currently there are 9 million homes with solid walls and no insulation.
Hadn't realise the Arotherm 3.5 is just the 5 with the badge and software changed. (how do you know?). So presumably the two units have exactly the same efficiency? They haven't changed the charge or anything else to optimise for lower power? That was my favourite unit so far (apart from the 3kW Geotherm I have in the extension which I could use if I could be bothered digging a big hole).
I have the full collection of Vaillant PDFs that are now being an approved installer login. The main 295 page technical document shows the 3.5 & 5kw to be the same as well as the 10 & 12kW You can also study the data on heatpumpmonitor which will bring you to the same conclusion.
My thoughts of the cosy are it just doesn’t have a big enough buffer for the property especially with the larger heat loss that this 10kwh is supposed to solve , especially with that graph to prevent that short cycling cycle I would expect a 50 litre or even 100 litre buffer on a 1600 ft property with average 9-15kwh heat loss and a lot of k2+ and k3, the amount of places that use old fashioned oil style rads really don’t work well with heat pumps so people just turn up to 5c more than what they would before under gas with a modern thermostat
It's been a while since I've watched HeatGeek channel, but generally buffers are not a good idea. If the system is designed properly / optimised, then there should be very few use-cases that require a buffer. I didn't know that my two-room Under Floor Heating should probably have its circulation pump and mixer valve removed ALTHOUGH I do hope to keep our 140litre heat-store which I think also better suits an ASHP, so maybe UFH alterations are not necessary.
I think the issue could be system volume rather than needing hydraulic separation, so perhaps a volumiser instead of a buffer would be necessary in some homes, as you say, dependant on system capacity of emitters and pipework.
@@terryjimfletcher As a general rule that is correct, but "some" designs need a buffer. Buffers increase install costs and reduce efficiency (increase running costs) so should not be fitted unless needed.
Very interesting video. From what I can understand about heat pumps, surely its best to accurately size or even slightly undersize them (rather than over). Particularly with the newer refrigerants, couldn't the flow temperature be tweaked up a little for the handful of days where the temperature is lower than the design scope. Even if that drops the efficiency a little on those few very coldest days, would you not win overall due to the milder shoulder months with the reduced cycling? You also mentioned several methods of calculating heat loss. I have tried Heatpunk, but I am keen to get a range of figures if possible. Could you please provide links to the others you were referring to?
Michael de podesta goes through the method of using your gas consumption to calculate heat loss. You can download the Assessment spreadsheet from the MCS website I think. Those are the other 2 methods available to all homeowners. In strict terms, undersizing can end up being worse than oversizing as you can get into defrost death spiralling and a cold house. Increasing flow temp won't solve that. Bear in mind, that most heat pumps will actually output more power at low flow temps than at higher ones. Sometimes a difference of 1kW can be seen on the spec sheet between 35-55 degree flow temps. BUT, all methods of heat loss calculation definitely leave a margin of error. Some say 10-20%.
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@@UpsideDownFork Thanks for that, I'll check both of those out. You have also recalibrated the way my brain thinks about flow temp, thanks.
Not sure what size we would need. 200m2 1980 and 2019 insulated home, 95kWh of gas a day between 15th Dec and 15th Feb usually. guessing that would be about 4kWh continuously.... But with the COSY tariff only being 8 hrs a day, would I want 3*4kW or a 12kW heat pump so I only run it for those 8 hrs?, or a battery sufficient to run it 24*7 at 4kW?
I would suggest you don't base your heat pump on a tariff, but the heat loss. Cosy won't be around forever and isn't necessarily the best option. @upsidedownfork uses Agile with his EV. Tracker and Go can also be good options.
Neither. I have 1913 vintage well insulated 200 sq m house and a 7kW heat pump plus a 10kWh battery, but the system is tuned to work hardest during cheapest cosy periods and then turn right down / off during most expensive. As such in cold weather we deliver up to 7kW for the cheapest periods into the DHW tank and also heating and then turn down for mid periods and right down in high periods. 86% of are energy is bought in the cheapest periods. 1% in most expensive.
@@andrewwright1200 have a look at the Heat Geek heat loss cheat sheet which offers a few rules of thumb that might apply. At 30W/m2 (recent new build range) you'd need 6kW, at 50W/m2 (renovated range) you'd need 10kW. Probably somewhere in the middle?
On the prairies, we need dehumidification in the summer. Just checking . . (Air source heat pump) I understand that an oversized heat pump wouldn't be on enough to manage dehumidification, without risking overcooling. Is that how it (doesn't) work?
Air to water ones generally don't do dehumidification... technically they can, but they need fan coils instead of radiators (and in some cases the cooling paid-for "DLC"). Air 2 Air ones however do dehumidification either when in cooling mode or "dry" mode which is basically a "soft cooling" mode. And yes, oversizing an Air 2 Air unit, will reduce it's ability to dehumidify effectively.
3 bed 1940s semi here - 79m2, cavity wall, loft insulation, double glazing... 7K heat loss. ...I've been waiting for them to do the upgraded version of the cosy, not the smaller one. I *dream* of being in a 3kw heat loss home, wow.
Seriously? Are you on gas? If so then how much gas do you use in a year. If it’s less than 15,000 kWh of gas then you need a maximum of a 5kW unit. If you are on oil if you use less than 1,500 litres then ditto. Personally I’ve never seen a house of your spec needing more than 5 kW (and we have fitted dozens of heat pumps over the past few years)
My house is 70m^2, similar double glazing, cavity wall, and minimal roof space insulation (no loft), my heat loss was calculated @ 5.2Kw. My Daikin 6kW HP is more than sufficient, so much so it runs at about 30%-50% output (30% down to 3C external) drawing typically 400-500W of electricity. That 7kW heat loss seems a bit on the high side.
@@UpsideDownFork The nuance about efficiency and cycling is beyond 95% of peoples comprehension ability. My gas boiler is way too big for my house, fitted by experienced and recommended plumbers (and lets face it they all have to be gas safe so not uneducated). They couldn't make Opentherm work with my Nest thermostat, it appeared to be a broken standard with no proper answer. A few years later I came to it myself and got it working. So now my way too big boiler works better at least. Next will be a heat pump but current boiler isn't super old yet though, so...
@@RichardABW Very true. We might need some mass re-education and approach it in the same way that we do with ICE cars. Everyone appreciates that they don't need a 5.0 V8 engine. These days, most people are happy with a 1.0 turbo if it reduces their bills.
It's the mindset of installers of the past and possibly the mindset of the same people who have or are about to migrate to installing heat pumps. About a year ago I watched a video about someone who had set up a training course for the industry in the aspects of low temperature CH. While the video was mainly positive the one comment that stuck with me was the number of people on that course that seemed unable to understand the basic maths associated with heat loss calculations and the sizing of ASHPs or modern gas condensing boilers.
Did a heat loss calculation for my 1970s 4 bed semi, worked out at 1.75kw (I have a installed 50cm of loft insulation and well sealed doors and windows) What heat pump options are there for this low?
Air to Air could be an option, e.g. a 4kW mutlisplit would modulate better than an A2W one. as long as you don't mind leaving interior doors open. Obviously don't get DHW. Vaillant's 3.5kW is just a nerfed 5kW model, you don't really get much more efficiency out of it, and it's worse for DHW. I know Urban Plumbers recommends installing the 5kW instead.
@@BenIsInSweden I was looking at the 3.5 Aerotherm and came across the same recommendation. I really want to get rid of the gas connection as we only use 5,000 kwh a year, so most months our standing charge is more than the usage. Hopefully a 2-3kwh heat pump will emerge in the future. I'm considering triple glazing and EWI and running the house on body heat in the future. 😀
@@andyca15forget the 3.5kW Vaillant cos it has the same minimum output as the 5kW and as such the 5kW will give you better performance in v cold weather and for hot water with no more cycling in mild weather than the 3.5. We fit loads of 5kW Vaillant units and never recommend the 3.5 for that reason.
Not enough is the short answer, sadly. But the other comments have covered things nicely. I'm very happy with my Vaillant Arotherm+ 7kW and wouldn't hesitate to recommend the 5 to others if it were suitable.
You prompted me to go through the data for every system on Open Heat Pump monitor. I have to question the data. Each data point is an average over 24 hours. This may mask a period where the heat output is at its maximum rated value to maintain the room temperatures. It is also curious how low the reported flow temperatures are. The majority are not breaking 30C. When I picked some systems and looked at the hourly data it does show some really high outputs. Secondly, Octopus are still installing Daikin heat pumps for larger houses, but they told me this week that this rarely allows them to install a system in a house with greater than 4 bedrooms. I assumed that they at least want to replace the Daikin installations with they Cosy 10 units.
True that the figures are averages but that's how a heat loss calculation is made. That is also an average. I've been surprised that my heat pump flow temperature is always a lot lower than I anticipated on weather compensation. Only when it got REALLY cold did mine go up to 40 degree flow. Perhaps the high outputs periods are the DHW cycle? Glad you took the time to look at the data for yourself and hopefully you still learnt something by doing so.
@@UpsideDownFork It was really useful for me, I am in the process of choosing a heat pump installer and I really want to avoid getting too big a heat pump. Looking at how many heat pumps are performing over 4.5 SCOP it may be that the UK is especially well suited to heatpumps as our country really is temperate. Mind you, I did use 45 000 KWh of gas last year so perhaps I do need a relatively large unit.
…I guess output, which does seem incredibly low. But I assume for constant heating. Fine for old folks who sit around at home all day. But most are out most of the day, so a waste to heat the house when not there. Then you need to size a heater to heat up the building when you are there, which how traditional systems are sized. Also if you have to run it continuously, you are not making best use of cheap rate electricity. So lose a small amount of efficiency, but halve your electricity rates?
@@markthomasson5077the heat pump is best for gradual heating. The waste can come from heating it fast. You use the temperature controls to heat from your chosen 'set back temp' back to your 'living temp'? Not so low that the heat pump struggles.
Figures shared here are the heat output. Low and slow also builds thermal mass into furniture, furnishings etc. It is so much more comfortable. I personally think it's best to find a balance between 24/7 steady heating and utilising smart tariffs. For me I turn the pump off 4-7pm and turn it down overnight. Otherwise it just runs throughout the day building up the thermal mass.
Octopus did the survey last week, waiting for final report, but sounds like the suggestion will be Cosy10. I'm in a 2017 built 4 bed 149sqm detached, I can't imagine that my heat loss justifies a 10kw... how can I be sure?
I'm in the same boat. Got the final proposal after the survey and with 5.9kW heat loss in an extended 1989, 112sqm , 4 bed detached with 10mm microbore and they are suggesting a Cosy 10 as well. I'm in 2 minds on it. I have asked about a Daikin 7kW but they are assuring me that the Cosy 10 is more efficient 🤷♂ Just seems like it'll spend it's life ticking over never getting anywhere near 6kW. Curious to know if you are going to go with the Cosy 10? I'm minded to trust them as it has the 8 year warranty and only £9pm for the servicing.
@@steve_787 If your heat loss is 5.9kW I would certainly not go for a Cosy 10. Early adopters of the Cosy 6 are not painting a good picture about it's efficiency. Daikin is a known quantity. The Daikin units up to 8kW perform very well.
Our heat loss came back just over 6kw, my attempt on heatpunk came to 5kw. So, I'm going for the Cosy10, apparently it's only 8.4kw. They don't have data sheets and I can't find it on MCS, so I negotiated a year free maintenance plan as a beta tester😁. From the figures they gave, it has better SCOP figures than the Cosy 6. So, let's see...
Do you know what the cosy 6 can modulate down to? I’m getting one installed next week and when adding my heat loss up on the radiator survey it is 2.7kw
Everything I have read supports what you are saying. My house is almost identical to yours at 142 sqm 1997 build 4 bed detached. Loft insultation not upgraded from the original 200mm but cavity has been filled. Octopus say Cosy 6 may not be big enough but Heat Geek estimate is 5.3kW. Octopus also want to fit a buffer but can't clearly articulate why. Pipework is copper 22mm main with 10mm tails to the rads and should not need a buffer if a volumizer is used.
Buffer losses can be minimised if you can match flow rates either side to limit distortion. My buffer is costing 5-10% in efficiency. The overall lifecycle cost of the cosy 6 will probably beat everything else, even if it can't hit those crazy high cops.
Had Octopus out to do their heat loss survey a week ago for the Cosy 10 (although I believe this will be a Cosy 9 now) and the surveyor couldn't find a single space anywhere around our house for it to sit. What with its size, the fact it needs to be mounted on the ground and can't be anywhere were propane will be an issue. We actually found one possible spot right on our only outdoor space for sitting in the sun or barbequing so that would have been a massive sacrifice for a heating system and it would need meters of extra piping (at an additional cost). So the survey was stopped and my deposit refunded I truly don't understand why Octopus designed the Cosy heat pumps the way they did, it looks odd and seems to be designed to make installation easier but at the detrement not finding a location for it. I have been able to find four other heat pumps (Vailliant, Ideal, Adlar castra and Aira) that all work perfectly at the side of my house so will be going with one of those.
@UpsideDownFork they looked at the Daikin units but they have a higher sound power making them too loud to install as it would fail MCS020 so required planning permission.
@@UpsideDownFork Yee the Vailliant seems to be the popular choice especially with the 7kw option I am tempted by the Adlar castra with its dual heat pump setup and overall price.
THe KW figures on the blue dots on your graphs, isn't that the average over the day? So as an example it could be putting in 10kw first thing in the monring when it's cold outside, then 3kw for the rest of the day after it warms up outside. Your average might be 5kw for the day, but you really needed the 10kw capacity heating the house in the morning.
That's a theory. Have a look at heat pump monitor closely yourself. If you find anyone that this applies to then let me know. What you'll find is that even when it's properly cold, only a small handful of pumps are putting out the heat loss figure and only for a very brief period. Don't forget that the heat output of a pump is limited by the compensation curve, emitters sizing and even pipe sizing.
If the AMOC collapses as soon as the latest science is projecting, we may be needing bigger heat pumps in the UK soon anyway. Something to factor into your thinking.
I've been speaking with octopus this afternoon and they are Quoting me £2970 for me to pay over the grant. This includes either a cosy 6 or 10 or a Daikin of eith capacity tank and radiator replacements and all fittings as required. This is for a 3 bed 110 sqm detached 80 year old house. I've got a 20 year old floor standing boiler and crappy un pressurized tank so seems like a no brainer to take the 10 if possible so that will give me headroom for an additional 48 sqm underfloor heated extension and loft extension....am I missing something in my assessment?
Depends on the heat loss calculation. A newly built extension will have a very low heat loss so will add a very small amount to what you already have. The price is a no brainer but I'd typically recommend that you push for the smallest heat pump that will cater for your property.
@@UpsideDownFork Thanks for the advice, the way they are rolling these out is that you get a Cosy 6 or equivalent if your heat loss is below 6 and if it's between 6 and 9 you get a 10 or equivalent. I guess from a speed of rollout and trying to get as many homes to convert as possible they have to streamline the product offering and optimise the speed so they are still making money after the Grant. I'm sure they are mindful that if the Grant stops then the whole transition market will just grind to a halt
Are you comparing you low flow temperature ashp that requires larger radiators with the cosy system with a flow of 70C that can almost be a like for like replacement for a gas boiler without having to alter radiators. Also consider that a large percentage of housing stock is a lot older than yours by many decades. Many have no cavity walls.
My Vaillant ASHP reaches a flow temp of 75 degrees. Both mine and the Cosy are incredibly inefficient when operating at those temps. It is all marketing. Octopus design their heating systems to a max of 50 degrees. My system is designed for a max of 45 degrees. You can hear more about this here: th-cam.com/video/Zw_MLhNzXEs/w-d-xo.html
My take on this is that bigger homes, means bigger incomes…more money to spend on upgrades….a bit like electric cars started on luxury and are now moving to cheaper end of market…why would you target cheap installations? Add to this ignorance….Ive heard heat pumps leave your house cold…not with a massive heat pump…sold, give me a big heat pump.
The very point I was going to make. Also, combined with Octopus variable tariffs and smart heating strategies you may need a larger heat pump for intentional cycling during off peak times
Sort of, I earn a decent packet but don't have the £20k needed for such upgrades. The house 2 doors down is a 3 bed council house, they just had at least £30k spent on upgrading courtesy of the tax payer. All those small heat pumps are going into social housing.
Any ashp owners out there with cold houses?!!? Mine's always 20-21.5°C. No drafts, no complaints from my wife (tbf my gas was heavily zoned and time restricted with Netatmo TRVs). Octopus calculated 8kw loss and fitted a 9kW Daikin. I wanted the 8kw as it's the small unit and my calcs said 7kw loss).
@@gregcarnall9097 unless it's a massive 4 bed, 5kw will be more than enough. Our 1996 built, 140sq M, 4 bed detached would be fine with 5kW so no doubt you would also 👍 Most of the popular heat pumps all function pretty similarly. I like my Vaillant a lot. It has one of the best apps and the physical control on the wall works well too. You won't go wrong with any of the heat pumps as long as you've got good support from your installer 👍
Sadly i live in a cottage thats over 200 years old. My gas boiler is 40kw and on very cold and windy days does not heat the house very well even though the walls are 18 inch to 2 feet thick. So a heat pump is not possible for this type of house.
Your gas boiler can only output as much heat as the radiators can emit. Unless your cottage is the size of Windsor castle, it is extremely unlikely that you have a 40kW heat loss. Limitation of your heating system is the same as many others, emitter sizing through proper heating design is critical.
@@UpsideDownFork I agree. It's not just a gas boiler or a heat pump but the rest of the system also needs to be designed to match the heat loss. The boiler may be 40kW but if the output of the radiators are only 5kW (at the selected operating flow temperature) then the boiler will switch off once the 5kW output is being met. The boiler is likely to be short cycling on and off. At the start of the fuel crisis the general advice was to set the boiler flow to 60C but if the radiators had been designed for 75C that meant that at 60C they may be only outputting 50% of the previous heat. This wouldn't have mattered much for the majority of people for perhaps 11+ months of the year but when the heat loss from the house is maximum during the coldest month the heating would be insufficient. The advice probably should have been to tweak the flow temperature up if the is a very cold spell of weather.
@@AlanMacleod-hv5ee True. Except for the fact that most radiators aren't correctly sized for any heat loss, they've been chronically oversized for decades and chosen by what fits under the windows and other such useless metrics. This is compounded by homes with original single glazing upgrading to double glazing and adding loft insulation. Once the heat loss has been reduced, the radiators become even more oversized. That's why we see so many heat pump upgrades that should need a tripling in radiator output, but often only need a couple of rads changed in the whole home. I turned our old gas boiler down from 70 degrees to 50 when it got really cold in the winter of 2022 and it still output too much, cycled frequently etc.
Oversized, maybe, but look at the room temps, if you only need 16'c then sure it's oversized at 10kw but personally around 21, ideally 22.5'c, then perhaps 10kw is a good size?
I will go against the trend (as all the live fishes do, I suppose) and claim that one should get slightly oversized HP for their property. First, theoretical calculations of heating capacity required tend to underrate the truly required heat output. Second, if you want to play a bit with lower-cost tariffs (like during the night), then you need more power of your HP to the heat loss during the expensive electricity period. Third, most HPs have better efficiencies when they work in lower modulation mode (I am currently looking at my Zubadan 8kW and Partload2 - one above theoretical min - is the most optimal mode). Fourth, bigger HPs usually come with bigger heat dissipation unit, hence don't need to compress the gas so much and lower the unit temperature, thus defrost cycles will be rarer. Fifth, you can quickly heat your hot domestic water if, for some reason, you ran out of it. Sixth, you can always get a 200/300L buffer and control the deltaT/flow speed to mitigate/avoid the dreaded frequent onoff switches.
@@BartoszBielecki disagree on the first three points. Complete opposite of what all the data tells us. Four and five are fair points but in no way outweigh the massive benefits of the other side.
10kw... is that a mid size house with paper for windows ?, My home is a little smaller than yours and 4 bed room is 4.8kw heat loss according to heat punk
I'm in Edwardian 4 bedroom with just original cavity walls + loft conversion with good insulation & new double glazed (within last 10-20 years), My peak heat use in January last year was max 4.5kW (average about 3kw) . I agree - nonsense. That said, surely the world needs a whole Russian doll set of these fugly unsustainable plastic monstrosities - so why not have even more sizes?! (I'm with Octopus - but I think their heat pumps just look awful on an epic scale all of their own - also most expensive install I've had quoted. Would never go with them)
From a novice such as oneself is it obvious that a 10kw heat pump would cost more to run than a 5kw , if so thought the whole point of people getting a heat pump was to be more efficient with generating heat for the home with cost in mind regarding the monthly bills , more concerning is if you can analyse being an intelligent let’s say amateur but with a diligent mindset then why can’t the so called professional not view it as you do , something not quite right going on with this company.
You have to fit a heat pump to match your properties needs though. No point fitting a 5kw heat pump in a 10kw heat loss property. Would mean a cold house and unsatisfied customer with "heat pumps don't work" type statements.
Some of this mentality seems a carry over from boiler fitting days. I don't blame anyone for erring on the side of caution a bit. A little oversizing isn't the end of the world...but some of the examples we see are very excessive. I was quoted for a 14kW unit myself. Madness. It was one of the things that BG got right for me. Their heat loss was spot on. Only thing that could have been improved would be a door blower test to get the correct air change rate.
The method itself is conservative. The surveyors don't want to leave people cold so err on the side of caution and then some of the heat pumps aren't clearly labelled. Compound those issues and you can end up considerably oversized.
SkillBuilder's Video. There's plenty of follow up to it, from Heat Geek on their own channel, and heat geek being featured on the Skill Builder channel. SB has kind of quietened down on the subject as the install that SB has featured on their channel that Heat Geek did has been surpassing all expectations, and SB will unlikely get the "ripping out the heat pump" content he desires so much.
I think octopus energy should stick with what they do best there heat pumps are not the best by a long way. He would be better off improving their customer service and ironing out the problems before the company ends up like the others 👍👍👍
I think they know what they're doing.They will likely end up being the biggest installer of heat pumps in the country, if they aren't already. Would be bizarre for them to just throw in the towel. Not to mention they are getting heat pumps into home at cost (to the buyer) comparable to a gas boiler, which looking at other youtube channels is not something that is very common.
Sorry IMHO, COSY is a massive failure. COP's are soo bad compared to even Low Temp Units. @ Flow Temp of 50'C you are better off with a Daikin Altherma 3 LT unit! Haven't even bothered to compare them to alternative High Temp Products
Your not really saving anything the price of the heat pump is that expensive, my new combi gas boiler cost £1950 fitted over a 10 year period would probably cost the same as a heat pump over that leanght of time, only thing your doing it putting out less pollution. I don't have £5000 to put a heat pump in!
@UpsideDownFork didn't get any quotes, I won't be buying one, and when 2034 comes, i will replace my gas boiler with a new gas boiler before they ban gas boilers , why would I want to get a heatpump that is so expensive and so complicated and just know it's just a money pit to maintain! No thanks!
@@davelocktalk so you haven't even got a quote but you say they're expensive? Emotive arguments never work with me. Come back when you've got some facts and figures and we'll chat. For me, in my home, a heat pump was cheaper to install, cheaper to run, warmer, more comfortable and cleaner. Winning.
Great video. Bob on. My 200 sq m 100yo 5 bed detached house has original windows with secondary glazing, insulated walls and a peak heat demand of 7kW. Last winter I ran on a 5kW LG which was adequate. The previous year I ran on a 6kW Ecodan which was also ok. This year am trialing a 7kW Vaillant which is probably the right one for the property with a bit of headroom going forward.
Thanks for sharing!
Yeah, over-sizing seems like a real issue still, some installers add their own buffer onto the heat loss calc which already has some some over-sizing built in from MCS requirements.
Buffers hold heat and reduce cycling. You should not add it to the calculation for heat loss. Its purely for increasing the amount of energy a single cycle can output and it will continue to distribute into the rads after the ashp is off.
It's ingrained into society that bigger = better - that's the reason - why else do people get 20+kW gas boilers (oh wait that's plumbers) - in fact my in-laws went for a 35kW oil boiler, just in case...
I did the calcs on Heatpunk for our 190m2 bungalow - 2001 build, reasonable insulation and newer glazing - it's on the verge of 7ish kW heat loss but that's for varying internal room temps of 15-19C rather than 21C - trying -3C or -5C and it starts to creep towards 8kW as well as tweaking the ventilation rates. So in principle something at 10kW might be useful, but this must be a less common need as you say.
Having a full range 4, 6, 8, 10 with the same underlying software and the relevant tweaked hardware to ensure reliability makes more sense to me...though with modulation across those ranges it shouldn't be an issue - I guess the hard bit is that for every drop in C temp the flow temp will tend to increase which then reduces output - there needs to be a clearer "marking" system i.e. Max output at -3C and 50C flow for example...
I did think the same when I heard about this. The thing is Octopus have smart meter data and access to customer addresses so should have a good idea on the heat demand during coldest days of the year before needing to even visit houses. I wouldn't be surprised if the houses they describe as poorly insulated have virtually no energy saving tech and people interested in heat pumps have a skewed view of a typical UK house. I think I heard that the majority were made pre-1920 but as you say I would love to see the data they used to decide that they needed a bigger unit first.
Good points 👍
I think its get a little messed up, as pre 1920's houses have more land - in our case we have loads of land based solar + existing oil heating = less than £1000 / year for everything in 2024 (incl running an EV), just fitting a 8kw HP to compliment to oil in winter.
Great info as always, Thank you
Thanks for watching!
Brilliant analysis. There should be a simple app that:
a) knows what the weather is doing at your location
b) allows you to record gas consumption in a 24 hour period (reading at start and then 24hrs later, e.g. 7pm-7pm
c) What temp you have set inside (and a nudge to keep it at this temp for 24 hours)
d) calculate what your heat loss is based on the above
e) reminds you to redo the above in all the following months
Exactly along the lines that I've been thinking.
Apparently the nest smart stat has the necessary data to extrapolate a heat loss from.
It is a good idea but there is one imponderable and that is establishing the efficiency of the boiler. I suspect there will be assumptions in the overall calculation.
@@UpsideDownFork There would still be problems with that approach. The gas consumption would have to be that for the coldest days during a 2 week period in winter (the coldest days will probably occur in February). You would have to make sure that your gas consumption was for all rooms being heated to, say, 20C and not the 12C for the room you don't use or the 16C that you like the bedrooms to be at. Under size your heat pump and you could be OK for 11 months of the year but it may not supply enough heat for 1 month of the year. Also there are heat pumps designed to work at lower temperatures (40 to 50C water flow temperatures) which in general need buildings with better insulation and large radiators and heat pumps that can work at 70C flow temperatures. The efficiency of a heat pump varies with temperature difference, a pump with a outside to water flow temperature difference of 40C will be more efficient than one designed to give a 70C difference. A ashp with a cop/scop figure of 1 difference means that the one with the lower cop/scop needs to be rated 25% higher. It has been stated that the average heat loss in UK homes is around 6kW BUT averages don't mean that much when selecting a suitable heat pump, many house would below this figure and many would be above. This puts the 6 and 10Kw Cosy ASHP in the correct ballpark for the range of UK homes.
..I do a lot of that with HomeAssistant.
Good video and I agree with you.The open energy monitor stuff is exciting stuff (if you are into geeking out) and the aggregated data is certainly showing that even amongst the geekiest of the designer and installers the oversizing is evident - and one of the reasons is the lack of true small capacity ASHPs. Of course the conundrum is once you are dropping below 5KW output that is impacting on the regeneration time of the hot water cylinder.
Anyone with a gas boiler who is seriously considering an ASHP and is thinking seriously of using the open energy monitoring kit, should give serious thought to buying the open energy monitoring kit now and installing it on their current system - it will do a much more accurate heat loss calculation and enable a better decision to be made on sizing the ASHP.
That's a great idea that I hadn't considered before!
@ I was thinking about this idea as it applies to me. I have a Viessmann 200 gas boiler running pure weather compensation (no internal room reference) on really low flow temperatures (for a gas boiler) and so it is actually running like a heat pump in winter (running 24/7).
@@normanboyes4983 My Veissman 100 system boiler won't run on a low temp. It cycles hopelessly, doing about 30 seconds on and 5 minutes off indefinitely after an initial 3-4 minute run, unless the temp dial is set to above 65C. I don't know what its algorithm is doing but I suspect it thinks the return temp is too high.
@@xxwookey I know nothing about the Viessman 100 and its performance characteristics. Having said that it does not sound right. How old is the boiler and how long has it been behaving like this?
Great video! Very informative
Thanks for watching!
I agree on my 4 bed house my heatpump sized 8.5 kw Ecodan . On heat pump monitor I never see
Higher than 2kw but still see to run in winter. Andrew Scotland
Winter is where things get interesting!
@@andrewdeans2179 What have you been seeing the last few days on heat pump monitor?
@ I have seen 4.2 kw as highest reading so still think heat pump oversized COP down to 3 but assume that’s OK house keeping temperature .
@ what ambient outside temp was that? What is the Design Outside Temp your location -4°C?
@ outside temp of -0.3 is reading heat pump monitor but was -3 overnight
Wholeheartedly agree they should have a COSY 4 Option, Our house 3 bedroom semi detached has a heatloss of just 2.1kw at -3.7c. We had the choice of the Cosy 6 or Daikin Altherma 3 and opted for the Daikin, I cannot see how the cosy would effeciently heat our home in typical mild weather without cycling.
I think the Daikin is a much better choice at the moment.
..yes, although a smaller market I guess - our house is quite large (250m2) and oldish (1950s/90s) heat demand is around 12kW on the EPC - even with loads of loft insulation, cavity walls insulation, DG etc.
So we have a 12kW Panasonic unit.
Not as closely monitored, but as an example -3 outside, 21 inside (overnight heat banking), 2.5kW IN to the heatpump
Overspeccing is far better than under-speccing - as if you do that you end up running in "kettle" mode too much of the time, and that kills the benefits
Thanks for commenting. Both undersizing and oversizing have pros and cons.
Enjoying your content [and others] while nursing my antique 16-22 Potterton boiler towards the end of its life in my 3 storey 1860s end-of-terrace home. I did do as much internal wall insulation as was feasible over 30yrs ago, it was somewhat 'experimental'. I wonder how the heat loss is estimated on party walls of terraces as you don't know how another home is occupied. My air changes/hr are probably a nightmare as the 3 floor stairwell acts like a chimney drawing heat upwards and cold in from below. Only the inner London heat island as a bonus...
Thanks for commenting!
Party walls use assumptions just as the rest of the heat loss calculation does. That's why this blunt instrument is ok, but far from perfect.
I need about 3 or 4kW, years ago I went and found myself a combi-boiler with very deep modulation, 12:1 as I wanted to avoid cycling due to wear and inefficiency.
Nice! Not many heat pumps to choose from in that lower range. Lots of options above 5.
HP modulation ratio seems to be fixed somewhat across brands and models, very different to boilers in that respect.
@@UpsideDownFork admittedly combiboilers are way too powerful for space heating, so 12:1 still only modulates down to about 2kW.
The thing is that Octopus' 3 rate tariff is designed to cause your heat pump to cycle during the day. To use the cheapest priced electricity you need a heatpump that can bring the home up to a high temp quickly during a 3 hour period and then stop for many hours before doing the same again.
That’s not actually realistic cos many houses will cool significantly in cold weather even during the 3 hours of the high price cosy period. More realistic is to do the hot water in cheapest period and then run heating reasonably hard for rest of cheap periods and then run heating at a lower level for the mid price periods. A battery also helps a lot! My pretty well insulated older house would be horrible if only heated in cheapest cosy periods
Other tariffs may be better for your household. I chose the Agile tariff for my heat pump and use (as did @upsidedownfork).
@@rogerthomas7040 the Cosy tariff is just one tariff. For my use (inc. heat pump) Agile and others are better.
My 1920 house high celling solid wall double glazed, r 15 recently topped up to r25 open space 3 sides getting a lot of wind , heat loss 22kwh still , in the end I went for a big gas boiler and don’t regret it one bit , this was after 3 different calculations, I just don’t get how the government think over 30% just can’t have heat pumps without over 20K of extra external insulation
@@Biggest-dh1vr I known them well as I'm currently on Agile. But if Octopus is expecting to offer more tariffs that have complex TOU pricing they would also focus on heat pumps that could still operate well, which would mean units not designed to operate all the time.
Completly agree here. Im just doing it my self on a grade EPC F house - a 6kw heat pump (will suffice) - as its the same pump irrespective as to whether you need 4Kw Hl or 8KW HL - its the same heat pump - I'm just keeping oil (as its 50p/l) just to fill those cold spots (albeits for the next few years to see how i get on). Would be great to know what you EPC rating is?
My latest EPC is an E but since then I've spent £6k on insulation materials, heat pump, solar panels, change all bulbs for LED etc. should bump it up a few of their arbitrary categories.
I have a 1952 three-bedroom property; I wouldn't say it is small - you could get a double-bed and change into every bedroom; and it has been insulated. Octopus have proposed to install a 4kW heat pump and that actually seems to be the right size based on some rule-of-thumb calculations I did based on my existing use of gas. So it does seem to me like a 10kW unit would be a monster!
That's reassuring to hear that you're getting a well sized heat pump.
Thank you.
Thanks for watching!
Not all of us are in the South of England. Quick heat pump calculations (based off current oil consumption) and I'm likely needing 8 to 10kW here in the North of Scotland.
As long as it modulates down.
Occasionally get weeks at -10C. Have seen as low as -29C (back in 2010).
6kW heat pump would likely work in a hybrid system, but you don't get grants for hybrid systems any more. It therefore needs to cope with actual cold, not just average cold. Daikin do one whereby only refrigerant is outside. That or air to air (and no grant) make more sense than most "water outside" heat pumps to many of us.
Your latitude doesn't make a difference to the usual heat loss calculation because usually they target -3 as the low temp. Your heat loss at -3C is the same in scotland as it is in england, its just much more likely to actually happen up in scotland, and way below -3 too. You can have your heat loss calc done for a lower temp outside, but that's not usually the assumption when people are quoting their heat loss figures.
@@jezlawrence720 My "local" site used for MCS heat loss calculations is Dyce (Aberdeen airport). that's relatively sheltered, relatively near the coast, and often a good 5C warmer than places using that as a reference. It's also the coldest mean air temperature of any of the 18 sites mentioned for the UK.
Even locally you can get massive differences in temperature due to topology. That -29C I mentioned was just the digital thermometer in my car, but within about 6 miles of Dyce where it was a nice and toasty -11C.
Point stands - heat pump needs to be able to handle properly cold for several days, otherwise it can't be the sole source of heating. You have to size it for that.
@@grahamleiper1538you might lose a few degrees in some rooms, but there's a bit of headroom in the output for when the temperature drops below the temperature used for the heat loss calculation.
Design a system for a 45 degree flow and when it gets colder for one or two days a year, you can always ramp the flow up to 50 or 55 and take the hit on efficiency, or you can allow your rooms to drop by 1 to 2 degrees during that time?
I take your point that some medium properties will indeed need 10kW. I just don't think that's a majority or even average case.
@@UpsideDownFork looking at the Heat Geek cheat sheet, 10kW would be enough for 150m2 at 65W/m2 (the worst case renovated cavity wall property). Or 90m2 of worst case Victorian or older single glazed.
One of the best economic cases for heatpumps is replacing oil boilers (that also need new oil tanks) on large old remote properties. Agree also wish to see lower powered heatpump or idealy two compressors so much high modulations range.
Good point. Thanks for commenting.
..or in our case LPG
Really we don't want a Cosy 4 product but an indoor wall mounted unit to replace a gas boiler. We already have A2A internal wall mounted units of 3.6kw so we just need a slightly different shaped A2W unit.
There are a load of people living in terraced, townhouse, flats that don't have a suitable outdoor space for a normal unit. Also I think many people in smaller houses would be more likely to consider one of you said it can go in the kitchen larder cupboard where there current gas boiler is. Also the less disruption the lower the install costs would be.
An indoor heat pump would be noisy , & have a fan blowing through the wall..
@brackcycle9056 They already exist in A2A form that you might have in a bedroom. So one in a kitchen isn't likely to be much of an issue noise wise.
Yes you would have a hole in the wall but you currently have one for your boiler flu so you would just have two rather than the current one you have with a gas boiler.
I support that!
The A2A wall mounted indoor units are connected with refrigerant lines to the outdoor heatpump unit.
@@danthep You are thinking of standard split AC units. They also sell units where everything is internal to the building. The only thing outside is an air flow in and exhaust vent.
An installer told me I needed 17kw, and that was after he assumed perfect insulation (which is nowhere even close), more like a barn with the door left open. I am on oil currently for about slightly over 300 m2 1904 property. In previous winters about 1000 liters of oil (or 10,000KWh of fuel) lasts about 2 months, so on average this is not even 1 liter per hour, so way less than their estimate, honestly I reckon 5kw in the background would take care of 90% of it. To the properties credit I did install under floor in ALL of the 300m2 which made a big difference, fortunatly its generally mild on the south coast. However cannot get the install as just does not tick the right boxes…
17?! Wow.
I've seen some of these properties where the installer fits 2 units in cadence to accommodate the high heat loss but the second unit only ever ends up doing DHW because the system of 2 pumps is ultimately oversized and unnecessary.
I didn't know before now, but oil/electric hybrid heat pumps do exist (Grant VortexAir is 17kW heat pump/26kW oil).
@@Biggest-dh1vr say goodby to any grant with that, but in principle as something that would cover you for those rare extra cold days, a nice idea
@@UpsideDownFork I agree, anyway it is only the wife and kids that complain whe it gets too cold!
Were a similar sized barn conversion with ok insulation in north wales and we came out with a heat loss of 11.5kw at -2.8. We were using 2500l of oil a year and nearly all underfloor heating. Testing running this on a Samsung 12kw gen6 but leaving oil in for backup and dhw for now and will see how it goes over winter and what the numbers show.
I think its usually a good idea to have a heat source that is significantly higher than the heat losses of the property. If the heat source was sized to match the heat losses then it would take a very long time for the property to reach a comfortable temperature and the source would be running 'flat-out' for extended periods. This may be why Octopus are suggesting that you should select a 10kW heat pump for a larger property even if your heat loss is much less.
The heat loss is designed to calculate the worst case situation, rather than a typical winter's day.
My own heat pump runs on minimum output for almost the entire heating season.
You can see more of this on heat pump monitor if you want to get into the weeds. There are none on there that are running flat out for extended periods, but in many ways that is better for the compressor than switching off and on all the time.
@@UpsideDownFork The fact that your heat pump is mostly running on minimum output sounds to me like it is sized correctly (or perhaps as you imply, its too big for your property), but this kind of proves my point that you need a heat source which is greater than the heat losses just to get things up to temperature before throttling back. I guess that this is unimportant if the heating is running 24/7 or the property is not subject to rapid changes in outside temperature. Apart from providing space heating, the heat pump also needs to provide additional heat for DHW and to recover the water temperature as quickly as possible. This is another reason why you might need a heat pump with a higher output than you might think.
@@tonydean7543if your heat loss at a sustained -3 degrees is 5kw then the required heat input at +5 degrees will be so much smaller that a 5kw heat pump will easily get things up to temp. In fact, a 5, 7 or 10kw unit won't put any more heat into the building any more quickly.
You are limited by weather compensation (flow temp), pipe sizing and emitter sizing.
Once you understand the relationship between these factors, you'll start to see that there is almost no case for oversizing a heat pump. The only time you could benefit may be when you have sustained periods far below your design temperature.
It just makes no sense to design a heating system for the 0.1% of the year, when we should be designing for the majority of the heating season 👍
Heat pumps have come a long way in terms of capability etc, however my mid 80's warm air gas heating system warms my open plan property quickly. Cavity wall insulation, double glazing and a well insulated loft plus global warming (milder weather) helps to keep the heating costs at a reasonable level. However i might move to a heat pump in the future.
@@specialandroid1603 thanks for having an open mind 👍
Cycling: different manufacturers have different control strategies. Vaillant Arotherm seems to be designed for cycling as a control strategy.
I do like Vaillant's approach. A deep look at the data shows that their variable DT does work quite well.
Cycling is inevitable for 95% of the year but short cycling is a different issue that can be avoided with the correct size pump and avoiding zoning.
@@UpsideDownFork I just noticed that my heat pump has almost stopped cycling now that it's colder.
I'm moving to a well insulated 2 bed detached bungalow, as a single householder. I think a small heat pump would suit me fine. As you say, I'd sooner it work efficiently for 95% of the time even if it struggled in exceptional weather. I wonder if Octopus still fit smaller (4Kw)? heat pumps from other manufacturers, like Daikin? I might try British Gas for my heat pump survey as I'm concerned that Octopus will recommend a Cosy 6.
Yes, you can still ask for a Daikin 4kw.
I agree they should have gone to a cosy 4 over a cosy 6, I've been looking into all this and in my new build house other than the environment effect having a heat pump makes no different for me on my gas bill, the only time I would save money in the long run would be is getting solar and battery's to run all the system as a hole but since I can't afford solar yet 😢 the heat pump will have to wait.
Utilising smart tariffs with a heat pump will see almost anyone save money on their energy bills but it won't be a lot.
I just had a blower test done on our house and it was way higher than expected. 4 ach. But as my hp has worked well never inputting more than 5kw. I assumed it must be more air tight. The mcs heatloss calculation is covering windy and cold day as the worst case. These are not that common where i am. We have mild windy days and still cold days generally. Hence its rare to get close to the heat that was calculated I suspect.
4 ACH? Wow! Have you tracked down the areas for improvement?
@@UpsideDownFork quite a few small ones. A particularly bad fireplace. But this is an 1870 terrace house that has had lots of work done but of varying quality. What it made me realise is it is not 4ach all the time it's very dependant on the wind and probably the direction too. I have some room for improvement...
Joe. Did your blower test adjust to normal pressure by dividing by 20?
@andrewcunningham1 no this was the ach50. I realise that the normal pressure it's way lower. But I guess what I had not considered was that drafts are just as variable as conductive heat losses. Some day you lose a lot others you lose a little.
@@joewentworth7856 Dividing by 20 brings your ACH down to a good low level. A brand new house is supposed to be about 0.3CH whereas yours is 0.2 ACH..so more airtight than a brand new house!
Epc F, 120 Square meters, having a 10kw fitted.
Thanks for commenting.
What we need is better heat loss measurements. Current system: homeowner has no idea. Even the best professional has to guess at some numbers, use guidelines, hope that what he can see represents what is hidden, etc. With this bad data he comes back to the homeowner with a heat loss number and a heat pump recommendation which sounds good, e.g. 9 kW heat loss 10 kW unit. You know looking at the specs that 10 kW unit means maybe 10 kW at some temperature but not every temperature, so the HP chosen only sounds good to the homeowner. Once he says "sure", that's the expensive thing he's stuck with until it wears out, no matter how wrong the professionals he relied on were.
Yep, more measurement and less estimating should be the future.
Lots of ways to do this and we have the technology already available.
@6:49. I think this one looks artificially worse because the three data points you look at the room temperatures are low (18.5,16.6,17.6). So they would be much higher if the room temperature was set to 20-21°c. But even so the 10kw unit is likely overkill and a 7kw would be the logical choice.
It seems somewhat pointless doing a heat loss calculation and then totally ignoring it! 😂
Good spot. Thanks for commenting!
1990’s house is modern really compared with millions of houses built before cavity walls. I wonder if any of those houses with heat pumps have solid walls. I have a gas boiler and it has to be on 8 hours a day when outside temps go below 5 degrees mainly due to the walls which suck heat out.
Not a problem.
Loads of solid stone walled properties are being successfully heated by a heat pump already.
@ but larger heat pumps will be needed to meet the demand is what I mean. Personal I will get EWI before installing a heat pump but many will not and so will need large unit. I personally think the gov should remove VAT from insulation products to encourage more people to insulate. But currently there are 9 million homes with solid walls and no insulation.
Hadn't realise the Arotherm 3.5 is just the 5 with the badge and software changed. (how do you know?). So presumably the two units have exactly the same efficiency? They haven't changed the charge or anything else to optimise for lower power? That was my favourite unit so far (apart from the 3kW Geotherm I have in the extension which I could use if I could be bothered digging a big hole).
I have the full collection of Vaillant PDFs that are now being an approved installer login.
The main 295 page technical document shows the 3.5 & 5kw to be the same as well as the 10 & 12kW
You can also study the data on heatpumpmonitor which will bring you to the same conclusion.
My thoughts of the cosy are it just doesn’t have a big enough buffer for the property especially with the larger heat loss that this 10kwh is supposed to solve , especially with that graph to prevent that short cycling cycle I would expect a 50 litre or even 100 litre buffer on a 1600 ft property with average 9-15kwh heat loss and a lot of k2+ and k3, the amount of places that use old fashioned oil style rads really don’t work well with heat pumps so people just turn up to 5c more than what they would before under gas with a modern thermostat
It's been a while since I've watched HeatGeek channel, but generally buffers are not a good idea. If the system is designed properly / optimised, then there should be very few use-cases that require a buffer.
I didn't know that my two-room Under Floor Heating should probably have its circulation pump and mixer valve removed ALTHOUGH I do hope to keep our 140litre heat-store which I think also better suits an ASHP, so maybe UFH alterations are not necessary.
I think the issue could be system volume rather than needing hydraulic separation, so perhaps a volumiser instead of a buffer would be necessary in some homes, as you say, dependant on system capacity of emitters and pipework.
@@terryjimfletcher As a general rule that is correct, but "some" designs need a buffer. Buffers increase install costs and reduce efficiency (increase running costs) so should not be fitted unless needed.
@@UpsideDownFork That is also my understanding.
Very interesting video.
From what I can understand about heat pumps, surely its best to accurately size or even slightly undersize them (rather than over). Particularly with the newer refrigerants, couldn't the flow temperature be tweaked up a little for the handful of days where the temperature is lower than the design scope. Even if that drops the efficiency a little on those few very coldest days, would you not win overall due to the milder shoulder months with the reduced cycling?
You also mentioned several methods of calculating heat loss. I have tried Heatpunk, but I am keen to get a range of figures if possible.
Could you please provide links to the others you were referring to?
Michael de podesta goes through the method of using your gas consumption to calculate heat loss.
You can download the Assessment spreadsheet from the MCS website I think.
Those are the other 2 methods available to all homeowners.
In strict terms, undersizing can end up being worse than oversizing as you can get into defrost death spiralling and a cold house. Increasing flow temp won't solve that.
Bear in mind, that most heat pumps will actually output more power at low flow temps than at higher ones. Sometimes a difference of 1kW can be seen on the spec sheet between 35-55 degree flow temps.
BUT, all methods of heat loss calculation definitely leave a margin of error. Some say 10-20%.
@@UpsideDownFork Thanks for that, I'll check both of those out.
You have also recalibrated the way my brain thinks about flow temp, thanks.
Not sure what size we would need. 200m2 1980 and 2019 insulated home, 95kWh of gas a day between 15th Dec and 15th Feb usually.
guessing that would be about 4kWh continuously....
But with the COSY tariff only being 8 hrs a day, would I want 3*4kW or a 12kW heat pump so I only run it for those 8 hrs?, or a battery sufficient to run it 24*7 at 4kW?
I would suggest you don't base your heat pump on a tariff, but the heat loss. Cosy won't be around forever and isn't necessarily the best option. @upsidedownfork uses Agile with his EV. Tracker and Go can also be good options.
Neither. I have 1913 vintage well insulated 200 sq m house and a 7kW heat pump plus a 10kWh battery, but the system is tuned to work hardest during cheapest cosy periods and then turn right down / off during most expensive. As such in cold weather we deliver up to 7kW for the cheapest periods into the DHW tank and also heating and then turn down for mid periods and right down in high periods. 86% of are energy is bought in the cheapest periods. 1% in most expensive.
Anything more than a 7/8kw pump is probably oversized. A decent heat loss survey is a key starting point.
@@andrewwright1200 have a look at the Heat Geek heat loss cheat sheet which offers a few rules of thumb that might apply. At 30W/m2 (recent new build range) you'd need 6kW, at 50W/m2 (renovated range) you'd need 10kW. Probably somewhere in the middle?
Remember that a battery to run a 4kW heatpump on full whack for 24 hours is about 24kWh, not 96kWh.
On the prairies, we need dehumidification in the summer. Just checking . . (Air source heat pump) I understand that an oversized heat pump wouldn't be on enough to manage dehumidification, without risking overcooling. Is that how it (doesn't) work?
Air to water ones generally don't do dehumidification... technically they can, but they need fan coils instead of radiators (and in some cases the cooling paid-for "DLC").
Air 2 Air ones however do dehumidification either when in cooling mode or "dry" mode which is basically a "soft cooling" mode. And yes, oversizing an Air 2 Air unit, will reduce it's ability to dehumidify effectively.
What he said! 😁
@@BenIsInSweden Thanks!
My house is 400 sqm built in 1899. Excited for the Still-not-Cosy 30, coming in 2032.
@@chrissrutt thanks for stopping by Chris, Earl of Rutt 😁
3 bed 1940s semi here - 79m2, cavity wall, loft insulation, double glazing... 7K heat loss.
...I've been waiting for them to do the upgraded version of the cosy, not the smaller one. I *dream* of being in a 3kw heat loss home, wow.
Seriously? Are you on gas? If so then how much gas do you use in a year. If it’s less than 15,000 kWh of gas then you need a maximum of a 5kW unit. If you are on oil if you use less than 1,500 litres then ditto. Personally I’ve never seen a house of your spec needing more than 5 kW (and we have fitted dozens of heat pumps over the past few years)
Don't know how 7kw was reached but sounds excessive.
My house is 70m^2, similar double glazing, cavity wall, and minimal roof space insulation (no loft), my heat loss was calculated @ 5.2Kw. My Daikin 6kW HP is more than sufficient, so much so it runs at about 30%-50% output (30% down to 3C external) drawing typically 400-500W of electricity.
That 7kW heat loss seems a bit on the high side.
There is/was always a mindset to oversize gas boilers, a bigger is better type thinking by people who don't know better. I guess the mindset persists.
Sadly it seems so.
@@UpsideDownFork The nuance about efficiency and cycling is beyond 95% of peoples comprehension ability.
My gas boiler is way too big for my house, fitted by experienced and recommended plumbers (and lets face it they all have to be gas safe so not uneducated). They couldn't make Opentherm work with my Nest thermostat, it appeared to be a broken standard with no proper answer. A few years later I came to it myself and got it working. So now my way too big boiler works better at least.
Next will be a heat pump but current boiler isn't super old yet though, so...
@@RichardABW Very true. We might need some mass re-education and approach it in the same way that we do with ICE cars. Everyone appreciates that they don't need a 5.0 V8 engine. These days, most people are happy with a 1.0 turbo if it reduces their bills.
It's the mindset of installers of the past and possibly the mindset of the same people who have or are about to migrate to installing heat pumps. About a year ago I watched a video about someone who had set up a training course for the industry in the aspects of low temperature CH. While the video was mainly positive the one comment that stuck with me was the number of people on that course that seemed unable to understand the basic maths associated with heat loss calculations and the sizing of ASHPs or modern gas condensing boilers.
@@AlanMacleod-hv5ee Maybe it's time for a formal separation between heating designers and heating installers?
Did a heat loss calculation for my 1970s 4 bed semi, worked out at 1.75kw (I have a installed 50cm of loft insulation and well sealed doors and windows) What heat pump options are there for this low?
3.5kW Vaillant Arotherm+ is your best bet. Might be a bit too much but then there are no gas boilers suitable for your heat loss either.
Air to Air could be an option, e.g. a 4kW mutlisplit would modulate better than an A2W one. as long as you don't mind leaving interior doors open.
Obviously don't get DHW.
Vaillant's 3.5kW is just a nerfed 5kW model, you don't really get much more efficiency out of it, and it's worse for DHW. I know Urban Plumbers recommends installing the 5kW instead.
@@BenIsInSweden I was looking at the 3.5 Aerotherm and came across the same recommendation.
I really want to get rid of the gas connection as we only use 5,000 kwh a year, so most months our standing charge is more than the usage.
Hopefully a 2-3kwh heat pump will emerge in the future.
I'm considering triple glazing and EWI and running the house on body heat in the future. 😀
@@andyca15forget the 3.5kW Vaillant cos it has the same minimum output as the 5kW and as such the 5kW will give you better performance in v cold weather and for hot water with no more cycling in mild weather than the 3.5. We fit loads of 5kW Vaillant units and never recommend the 3.5 for that reason.
Not enough is the short answer, sadly.
But the other comments have covered things nicely.
I'm very happy with my Vaillant Arotherm+ 7kW and wouldn't hesitate to recommend the 5 to others if it were suitable.
You prompted me to go through the data for every system on Open Heat Pump monitor. I have to question the data. Each data point is an average over 24 hours. This may mask a period where the heat output is at its maximum rated value to maintain the room temperatures. It is also curious how low the reported flow temperatures are. The majority are not breaking 30C. When I picked some systems and looked at the hourly data it does show some really high outputs. Secondly, Octopus are still installing Daikin heat pumps for larger houses, but they told me this week that this rarely allows them to install a system in a house with greater than 4 bedrooms. I assumed that they at least want to replace the Daikin installations with they Cosy 10 units.
True that the figures are averages but that's how a heat loss calculation is made. That is also an average.
I've been surprised that my heat pump flow temperature is always a lot lower than I anticipated on weather compensation.
Only when it got REALLY cold did mine go up to 40 degree flow.
Perhaps the high outputs periods are the DHW cycle?
Glad you took the time to look at the data for yourself and hopefully you still learnt something by doing so.
@@UpsideDownFork It was really useful for me, I am in the process of choosing a heat pump installer and I really want to avoid getting too big a heat pump. Looking at how many heat pumps are performing over 4.5 SCOP it may be that the UK is especially well suited to heatpumps as our country really is temperate. Mind you, I did use 45 000 KWh of gas last year so perhaps I do need a relatively large unit.
Of course I didn't. I am fed up with those summits
@@TheAllMightyGodofCod I don't blame you.
Are you talking about the output of the heater, or the (3-4times lower) input to the heat pump?
…I guess output, which does seem incredibly low. But I assume for constant heating. Fine for old folks who sit around at home all day. But most are out most of the day, so a waste to heat the house when not there. Then you need to size a heater to heat up the building when you are there, which how traditional systems are sized.
Also if you have to run it continuously, you are not making best use of cheap rate electricity. So lose a small amount of efficiency, but halve your electricity rates?
@@markthomasson5077the heat pump is best for gradual heating. The waste can come from heating it fast. You use the temperature controls to heat from your chosen 'set back temp' back to your 'living temp'? Not so low that the heat pump struggles.
Figures shared here are the heat output.
Low and slow also builds thermal mass into furniture, furnishings etc.
It is so much more comfortable.
I personally think it's best to find a balance between 24/7 steady heating and utilising smart tariffs.
For me I turn the pump off 4-7pm and turn it down overnight. Otherwise it just runs throughout the day building up the thermal mass.
Octopus did the survey last week, waiting for final report, but sounds like the suggestion will be Cosy10. I'm in a 2017 built 4 bed 149sqm detached, I can't imagine that my heat loss justifies a 10kw... how can I be sure?
Our 1996 built 140SqM has a heat loss of under 6kW.
You can perform your own heat loss with the help of heatpunk if you're reasonable with a computer.
I'm in the same boat. Got the final proposal after the survey and with 5.9kW heat loss in an extended 1989, 112sqm , 4 bed detached with 10mm microbore and they are suggesting a Cosy 10 as well. I'm in 2 minds on it. I have asked about a Daikin 7kW but they are assuring me that the Cosy 10 is more efficient 🤷♂ Just seems like it'll spend it's life ticking over never getting anywhere near 6kW. Curious to know if you are going to go with the Cosy 10? I'm minded to trust them as it has the 8 year warranty and only £9pm for the servicing.
I'm still waiting for the survey report. I started with my own heatpunk survey, hoping to get the survey so I don't need to measure everything.
@@steve_787 If your heat loss is 5.9kW I would certainly not go for a Cosy 10.
Early adopters of the Cosy 6 are not painting a good picture about it's efficiency. Daikin is a known quantity. The Daikin units up to 8kW perform very well.
Our heat loss came back just over 6kw, my attempt on heatpunk came to 5kw. So, I'm going for the Cosy10, apparently it's only 8.4kw. They don't have data sheets and I can't find it on MCS, so I negotiated a year free maintenance plan as a beta tester😁. From the figures they gave, it has better SCOP figures than the Cosy 6. So, let's see...
When I spoke to the octopus engineer he'd just come from a HMO. maybe this this what the bigger cosy is aimed at?
Fair point!
I live on the 10th floor tower block
How do i get a heat pump you tell me
Air to air heat pump if you own or district heating if you rent.
@@UpsideDownFork oh what load of BS
Do you know what the cosy 6 can modulate down to? I’m getting one installed next week and when adding my heat loss up on the radiator survey it is 2.7kw
Cosy 6 can allegedly modulate down to 1.9kW
Everything I have read supports what you are saying. My house is almost identical to yours at 142 sqm 1997 build 4 bed detached. Loft insultation not upgraded from the original 200mm but cavity has been filled. Octopus say Cosy 6 may not be big enough but Heat Geek estimate is 5.3kW. Octopus also want to fit a buffer but can't clearly articulate why. Pipework is copper 22mm main with 10mm tails to the rads and should not need a buffer if a volumizer is used.
Buffer losses can be minimised if you can match flow rates either side to limit distortion.
My buffer is costing 5-10% in efficiency.
The overall lifecycle cost of the cosy 6 will probably beat everything else, even if it can't hit those crazy high cops.
Had Octopus out to do their heat loss survey a week ago for the Cosy 10 (although I believe this will be a Cosy 9 now) and the surveyor couldn't find a single space anywhere around our house for it to sit. What with its size, the fact it needs to be mounted on the ground and can't be anywhere were propane will be an issue. We actually found one possible spot right on our only outdoor space for sitting in the sun or barbequing so that would have been a massive sacrifice for a heating system and it would need meters of extra piping (at an additional cost). So the survey was stopped and my deposit refunded I truly don't understand why Octopus designed the Cosy heat pumps the way they did, it looks odd and seems to be designed to make installation easier but at the detrement not finding a location for it.
I have been able to find four other heat pumps (Vailliant, Ideal, Adlar castra and Aira) that all work perfectly at the side of my house so will be going with one of those.
Octopus still offer Daikin R32 units that can be situated anywhere.
I'm surprised your surveyor didn't offer this option.
@UpsideDownFork they looked at the Daikin units but they have a higher sound power making them too loud to install as it would fail MCS020 so required planning permission.
@clarkfinlay78 ah, got it! I'm very happy with my Vaillant 😊
@@UpsideDownFork Yee the Vailliant seems to be the popular choice especially with the 7kw option I am tempted by the Adlar castra with its dual heat pump setup and overall price.
THe KW figures on the blue dots on your graphs, isn't that the average over the day? So as an example it could be putting in 10kw first thing in the monring when it's cold outside, then 3kw for the rest of the day after it warms up outside. Your average might be 5kw for the day, but you really needed the 10kw capacity heating the house in the morning.
That's a theory. Have a look at heat pump monitor closely yourself.
If you find anyone that this applies to then let me know.
What you'll find is that even when it's properly cold, only a small handful of pumps are putting out the heat loss figure and only for a very brief period.
Don't forget that the heat output of a pump is limited by the compensation curve, emitters sizing and even pipe sizing.
@UpsideDownFork yes it wouldn't make much sense putting in a 10kW heat pump if your radiators can only put out 3kW
If the AMOC collapses as soon as the latest science is projecting, we may be needing bigger heat pumps in the UK soon anyway. Something to factor into your thinking.
That's an interesting thought.
Is the heat loss given per day or per hr? Just had a survey done by Octopus and they're pushing for Cosy 6. I'm pushing for Daikin ;)
@@MotivatedAcademic the headline figure is typically kW per hour.
@@UpsideDownFork thanks, we're at 3.7 kW loss so 6 kW Cosy would be quite oversized...
I've been speaking with octopus this afternoon and they are Quoting me £2970 for me to pay over the grant. This includes either a cosy 6 or 10 or a Daikin of eith capacity tank and radiator replacements and all fittings as required. This is for a 3 bed 110 sqm detached 80 year old house. I've got a 20 year old floor standing boiler and crappy un pressurized tank so seems like a no brainer to take the 10 if possible so that will give me headroom for an additional 48 sqm underfloor heated extension and loft extension....am I missing something in my assessment?
Depends on the heat loss calculation. A newly built extension will have a very low heat loss so will add a very small amount to what you already have.
The price is a no brainer but I'd typically recommend that you push for the smallest heat pump that will cater for your property.
@@UpsideDownFork Thanks for the advice, the way they are rolling these out is that you get a Cosy 6 or equivalent if your heat loss is below 6 and if it's between 6 and 9 you get a 10 or equivalent. I guess from a speed of rollout and trying to get as many homes to convert as possible they have to streamline the product offering and optimise the speed so they are still making money after the Grant. I'm sure they are mindful that if the Grant stops then the whole transition market will just grind to a halt
Are you comparing you low flow temperature ashp that requires larger radiators with the cosy system with a flow of 70C that can almost be a like for like replacement for a gas boiler without having to alter radiators. Also consider that a large percentage of housing stock is a lot older than yours by many decades. Many have no cavity walls.
My Vaillant ASHP reaches a flow temp of 75 degrees. Both mine and the Cosy are incredibly inefficient when operating at those temps. It is all marketing.
Octopus design their heating systems to a max of 50 degrees. My system is designed for a max of 45 degrees.
You can hear more about this here:
th-cam.com/video/Zw_MLhNzXEs/w-d-xo.html
My take on this is that bigger homes, means bigger incomes…more money to spend on upgrades….a bit like electric cars started on luxury and are now moving to cheaper end of market…why would you target cheap installations? Add to this ignorance….Ive heard heat pumps leave your house cold…not with a massive heat pump…sold, give me a big heat pump.
The very point I was going to make. Also, combined with Octopus variable tariffs and smart heating strategies you may need a larger heat pump for intentional cycling during off peak times
Fair point, well made.
Sort of, I earn a decent packet but don't have the £20k needed for such upgrades. The house 2 doors down is a 3 bed council house, they just had at least £30k spent on upgrading courtesy of the tax payer. All those small heat pumps are going into social housing.
Any ashp owners out there with cold houses?!!?
Mine's always 20-21.5°C. No drafts, no complaints from my wife (tbf my gas was heavily zoned and time restricted with Netatmo TRVs).
Octopus calculated 8kw loss and fitted a 9kW Daikin. I wanted the 8kw as it's the small unit and my calcs said 7kw loss).
Hi, i have a new 4 bed house built in 2023, do you think a 5kw would be on for me, also who do you think make the best heat pumps? Many thanks
@@gregcarnall9097 unless it's a massive 4 bed, 5kw will be more than enough. Our 1996 built, 140sq M, 4 bed detached would be fine with 5kW so no doubt you would also 👍
Most of the popular heat pumps all function pretty similarly. I like my Vaillant a lot. It has one of the best apps and the physical control on the wall works well too.
You won't go wrong with any of the heat pumps as long as you've got good support from your installer 👍
Well I have 4 bed house heat loss 12 KW so I want them to bring out a cosy12. I consider my house upper med
How did you get to that figure? Do you not have any wall or loft insulation? Maybe no double glazing?
@UpsideDownFork yes double glazing and roof insulation but solid walls all round which is a killer
Sadly i live in a cottage thats over 200 years old. My gas boiler is 40kw and on very cold and windy days does not heat the house very well even though the walls are 18 inch to 2 feet thick. So a heat pump is not possible for this type of house.
Your gas boiler can only output as much heat as the radiators can emit.
Unless your cottage is the size of Windsor castle, it is extremely unlikely that you have a 40kW heat loss.
Limitation of your heating system is the same as many others, emitter sizing through proper heating design is critical.
@@UpsideDownFork I agree. It's not just a gas boiler or a heat pump but the rest of the system also needs to be designed to match the heat loss. The boiler may be 40kW but if the output of the radiators are only 5kW (at the selected operating flow temperature) then the boiler will switch off once the 5kW output is being met. The boiler is likely to be short cycling on and off. At the start of the fuel crisis the general advice was to set the boiler flow to 60C but if the radiators had been designed for 75C that meant that at 60C they may be only outputting 50% of the previous heat. This wouldn't have mattered much for the majority of people for perhaps 11+ months of the year but when the heat loss from the house is maximum during the coldest month the heating would be insufficient. The advice probably should have been to tweak the flow temperature up if the is a very cold spell of weather.
@@AlanMacleod-hv5ee True. Except for the fact that most radiators aren't correctly sized for any heat loss, they've been chronically oversized for decades and chosen by what fits under the windows and other such useless metrics.
This is compounded by homes with original single glazing upgrading to double glazing and adding loft insulation.
Once the heat loss has been reduced, the radiators become even more oversized.
That's why we see so many heat pump upgrades that should need a tripling in radiator output, but often only need a couple of rads changed in the whole home.
I turned our old gas boiler down from 70 degrees to 50 when it got really cold in the winter of 2022 and it still output too much, cycled frequently etc.
Good content other than the tutting.
Thanks for the feedback!
Oversized, maybe, but look at the room temps, if you only need 16'c then sure it's oversized at 10kw but personally around 21, ideally 22.5'c, then perhaps 10kw is a good size?
That's a good point that needs more investigation for sure.
Heat pump monitor has so much valuable data to study!
I will go against the trend (as all the live fishes do, I suppose) and claim that one should get slightly oversized HP for their property. First, theoretical calculations of heating capacity required tend to underrate the truly required heat output. Second, if you want to play a bit with lower-cost tariffs (like during the night), then you need more power of your HP to the heat loss during the expensive electricity period. Third, most HPs have better efficiencies when they work in lower modulation mode (I am currently looking at my Zubadan 8kW and Partload2 - one above theoretical min - is the most optimal mode). Fourth, bigger HPs usually come with bigger heat dissipation unit, hence don't need to compress the gas so much and lower the unit temperature, thus defrost cycles will be rarer. Fifth, you can quickly heat your hot domestic water if, for some reason, you ran out of it. Sixth, you can always get a 200/300L buffer and control the deltaT/flow speed to mitigate/avoid the dreaded frequent onoff switches.
@@BartoszBielecki disagree on the first three points. Complete opposite of what all the data tells us.
Four and five are fair points but in no way outweigh the massive benefits of the other side.
10kw... is that a mid size house with paper for windows ?, My home is a little smaller than yours and 4 bed room is 4.8kw heat loss according to heat punk
I think you are supposed to heat the cardboard box that the Cosy 10 kW comes in.
I'm in Edwardian 4 bedroom with just original cavity walls + loft conversion with good insulation & new double glazed (within last 10-20 years), My peak heat use in January last year was max 4.5kW (average about 3kw) . I agree - nonsense.
That said, surely the world needs a whole Russian doll set of these fugly unsustainable plastic monstrosities - so why not have even more sizes?!
(I'm with Octopus - but I think their heat pumps just look awful on an epic scale all of their own - also most expensive install I've had quoted. Would never go with them)
Thanks for sharing!
The future does look weird with Cosy 2, 4, 6, 8, 10, 14 and on...
Conclusion:- don't trust an energy company to fit an efficient heating system...
Maybe, maybe not. Jury is out on this so far.
From a novice such as oneself is it obvious that a 10kw heat pump would cost more to run than a 5kw , if so thought the whole point of people getting a heat pump was to be more efficient with generating heat for the home with cost in mind regarding the monthly bills , more concerning is if you can analyse being an intelligent let’s say amateur but with a diligent mindset then why can’t the so called professional not view it as you do , something not quite right going on with this company.
You have to fit a heat pump to match your properties needs though.
No point fitting a 5kw heat pump in a 10kw heat loss property. Would mean a cold house and unsatisfied customer with "heat pumps don't work" type statements.
@@Lewis_Standing From what I’ve seen and heard lots of unhappy customers because their heat pump has been seized incorrectly by cowboys,
Some of this mentality seems a carry over from boiler fitting days.
I don't blame anyone for erring on the side of caution a bit. A little oversizing isn't the end of the world...but some of the examples we see are very excessive.
I was quoted for a 14kW unit myself. Madness. It was one of the things that BG got right for me. Their heat loss was spot on. Only thing that could have been improved would be a door blower test to get the correct air change rate.
Is this more about incompetent heat loss surveyors covering their backsides?
The method itself is conservative. The surveyors don't want to leave people cold so err on the side of caution and then some of the heat pumps aren't clearly labelled.
Compound those issues and you can end up considerably oversized.
google "This is Why Heat Pumps May NOT Be The Future"
Just comes up with a load of FUD for me.
SkillBuilder's Video. There's plenty of follow up to it, from Heat Geek on their own channel, and heat geek being featured on the Skill Builder channel. SB has kind of quietened down on the subject as the install that SB has featured on their channel that Heat Geek did has been surpassing all expectations, and SB will unlikely get the "ripping out the heat pump" content he desires so much.
Octopus suckered
🐙
@UpsideDownFork
You truly are an alcoholic
I think octopus energy should stick with what they do best there heat pumps are not the best by a long way. He would be better off improving their customer service and ironing out the problems before the company ends up like the others 👍👍👍
I think they know what they're doing.They will likely end up being the biggest installer of heat pumps in the country, if they aren't already. Would be bizarre for them to just throw in the towel. Not to mention they are getting heat pumps into home at cost (to the buyer) comparable to a gas boiler, which looking at other youtube channels is not something that is very common.
Vertical integration for home energy and technology will be powerful.
I think we will see a LOT of these cosys everywhere in the coming years.
Sorry IMHO, COSY is a massive failure. COP's are soo bad compared to even Low Temp Units. @ Flow Temp of 50'C you are better off with a Daikin Altherma 3 LT unit!
Haven't even bothered to compare them to alternative High Temp Products
Have you seen the data in the real world of the Cosy 6?
Your not really saving anything the price of the heat pump is that expensive, my new combi gas boiler cost £1950 fitted over a 10 year period would probably cost the same as a heat pump over that leanght of time, only thing your doing it putting out less pollution. I don't have £5000 to put a heat pump in!
Many people are getting octopus heat pumps installed for £500-£1000.
@UpsideDownFork not in my old house
@@davelocktalk How much did they quote you?
@UpsideDownFork didn't get any quotes, I won't be buying one, and when 2034 comes, i will replace my gas boiler with a new gas boiler before they ban gas boilers , why would I want to get a heatpump that is so expensive and so complicated and just know it's just a money pit to maintain! No thanks!
@@davelocktalk so you haven't even got a quote but you say they're expensive? Emotive arguments never work with me.
Come back when you've got some facts and figures and we'll chat.
For me, in my home, a heat pump was cheaper to install, cheaper to run, warmer, more comfortable and cleaner. Winning.