There's an interesting video by Technology Connections where on a very cold night, he switched off the heating system and used small electric heaters to maintain the house temperature. He recorded temperature and power use for the heaters. Because electric resistance heating is 100% efficient, you can get a useful answer with a careful experiment design.
Just getting into this myself. Even though I'm experienced engineer with knowledge/ experience of heat transfer coefficients and all that stuff I can't quite my head around necessity of doing all this intense survey work . I understand it if its a new build - never lived in. But assuming its been lived in you can work out the total bulk heat loss from your house simply by looking at your gas usage in winter months. I note 2,000 kwh used for for whole of January 2024 - which was just below an average temperature January. Divide by 31 and 24 ~ 2.7kW average. It peaked on a particular 2 days at 4kw. So I can't understand why any more that would be required - empiraclk evidence rather than potentially quite sketchy hand calculations - which inevitable have a lot of guesswork. It doesn't give you a look at individual rooms mind. Secondly in calculating losses form analytic formula I notice that whilst you can set an outside temperature none of them appear to include wind speed. Everyone has heard of windchill effective temperature - so a very windy day at +3C easily has potential cool down your house much more than stlill day at -3C. But doenst appear in the input parameters - unless i missed it.
There is a method that uses degree days and your total gas use, to give you a rough idea of your maximum heat loss figure. This is a pretty common rule of thumb, even if I don't think it's very accurate. Here is a good article on it if you've not heard of it before - protonsforbreakfast.wordpress.com/2022/03/15/heating-degree-days4three-numbers-you-need-to-know-about-your-home/ That said, room by room calculations are needed so that appropriate radiators can be put in. Outside temp is used. There are ways to factor in the exposure of a building and how to factor in additional loses due to wind. These are covered by SAP, which is a more detailed process for heat loss, but it's not really used I don't think. Once a heat loss has been calculated on paper, a heat source with a little overhead is added. If you had a heat loss at 7kW, you might choose an 8kW or 9kW heat source, so you have a little slack. I'd be told to design for about -3 in the west midlands, but I've seen a week at -5. I'm not an expert in any of this, so please take my words with a little pinch of salt!
Hi Tom, Can you not put Walltite in the cavity of your bathroom. It would work well on the roof of your garage instead of insulating the bathroom floor.
I have never heard of that! I’m a bit cautious with foam type insulation, since it’s very hard to remove should something go wrong. I’ll certainly have a look at that! Thanks! I put insulation into the garage ceiling already. 150mm of rockwool.
Hi Tom, Really appreciate your heard work for getting all information at one place. I need to have my ASHP and getting very high quotes, want to DIY by following you, my question is can I claim my grant by doing it DIY? Thanks
So….as I understand it, it *might* be possible to get the grant if you use an MCS umbrella scheme. I’m not 100% on this yet. I need to do a lot of homework!
@@tomasmcguinness Appreciate your quick response and will wait for your video about getting grant via MCS umbrella, The MCS registered people exploiting general public by quoting huge money.
Good stuff, careful with the way Valliant badge heatpumps. Urban plumber spoke about it recently but a 7kw heat pump at 40c flow at -3c is actually 8.6kwh heat so you could have some unwanted cycling. If you can bring your heat loss closer to 6.4kwh you could get a 5kw heatpump though. So maybe a new frontdoor etc or 350 or 400mm in the loft etc.
Thanks!! I need to do lots more research here and as you say more fabric work might help. I really do need a new front door, even just for air tightness!!
Hi, I don't know if you go away in the heating season but if you do then with a heat pump it can take a few days for the house temperature to return to the usual levels in your home when you return. You could leave your gas boiler installed and then have a lever so that you can divert the gas boiler CHW into your home.
Ran into that once a few years back, in our old house. Went away over Christmas and it took the house three days to recover 🤣 far more organised now and then the heating on a day or two before we come home. I’m already running my boiler’s temp really low, like a heat pump. This house is much more insulated, so it warms up much faster too.
Great work Tom, thanks for walking us through the calculations.
Thanks!!
There's an interesting video by Technology Connections where on a very cold night, he switched off the heating system and used small electric heaters to maintain the house temperature. He recorded temperature and power use for the heaters. Because electric resistance heating is 100% efficient, you can get a useful answer with a careful experiment design.
Just getting into this myself. Even though I'm experienced engineer with knowledge/ experience of heat transfer coefficients and all that stuff I can't quite my head around necessity of doing all this intense survey work . I understand it if its a new build - never lived in. But assuming its been lived in you can work out the total bulk heat loss from your house simply by looking at your gas usage in winter months. I note 2,000 kwh used for for whole of January 2024 - which was just below an average temperature January. Divide by 31 and 24 ~ 2.7kW average. It peaked on a particular 2 days at 4kw. So I can't understand why any more that would be required - empiraclk evidence rather than potentially quite sketchy hand calculations - which inevitable have a lot of guesswork. It doesn't give you a look at individual rooms mind.
Secondly in calculating losses form analytic formula I notice that whilst you can set an outside temperature none of them appear to include wind speed. Everyone has heard of windchill effective temperature - so a very windy day at +3C easily has potential cool down your house much more than stlill day at -3C. But doenst appear in the input parameters - unless i missed it.
There is a method that uses degree days and your total gas use, to give you a rough idea of your maximum heat loss figure. This is a pretty common rule of thumb, even if I don't think it's very accurate. Here is a good article on it if you've not heard of it before - protonsforbreakfast.wordpress.com/2022/03/15/heating-degree-days4three-numbers-you-need-to-know-about-your-home/
That said, room by room calculations are needed so that appropriate radiators can be put in.
Outside temp is used. There are ways to factor in the exposure of a building and how to factor in additional loses due to wind. These are covered by SAP, which is a more detailed process for heat loss, but it's not really used I don't think.
Once a heat loss has been calculated on paper, a heat source with a little overhead is added. If you had a heat loss at 7kW, you might choose an 8kW or 9kW heat source, so you have a little slack. I'd be told to design for about -3 in the west midlands, but I've seen a week at -5.
I'm not an expert in any of this, so please take my words with a little pinch of salt!
Hi Tom, Can you not put Walltite in the cavity of your bathroom. It would work well on the roof of your garage instead of insulating the bathroom floor.
I have never heard of that! I’m a bit cautious with foam type insulation, since it’s very hard to remove should something go wrong. I’ll certainly have a look at that! Thanks! I put insulation into the garage ceiling already. 150mm of rockwool.
Hi Tom,
Really appreciate your heard work for getting all information at one place. I need to have my ASHP and getting very high quotes, want to DIY by following you, my question is can I claim my grant by doing it DIY? Thanks
So….as I understand it, it *might* be possible to get the grant if you use an MCS umbrella scheme. I’m not 100% on this yet. I need to do a lot of homework!
@@tomasmcguinness Appreciate your quick response and will wait for your video about getting grant via MCS umbrella, The MCS registered people exploiting general public by quoting huge money.
Good stuff, careful with the way Valliant badge heatpumps. Urban plumber spoke about it recently but a 7kw heat pump at 40c flow at -3c is actually 8.6kwh heat so you could have some unwanted cycling. If you can bring your heat loss closer to 6.4kwh you could get a 5kw heatpump though. So maybe a new frontdoor etc or 350 or 400mm in the loft etc.
Thanks!! I need to do lots more research here and as you say more fabric work might help. I really do need a new front door, even just for air tightness!!
Hi, I don't know if you go away in the heating season but if you do then with a heat pump it can take a few days for the house temperature to return to the usual levels in your home when you return. You could leave your gas boiler installed and then have a lever so that you can divert the gas boiler CHW into your home.
Ran into that once a few years back, in our old house. Went away over Christmas and it took the house three days to recover 🤣 far more organised now and then the heating on a day or two before we come home. I’m already running my boiler’s temp really low, like a heat pump. This house is much more insulated, so it warms up much faster too.
@@tomasmcguinness Yes the ability to turn your heating on remotely is the key.
It was a game changer. First smart thermostat I had was a Nest. The remote control was the *only* thing we actually used 😂