วีดีโอ

Thank you.

Yes they are fragile, as seen in some of my other videos. I demoulded after a few hours as alumina cement reaches initial cure quickly. My feeling is that it is the perlite that weakens the mix although agree the fireclay may contribute. I still used all my parts by gluing them together with a stiff paste made by mixing powdered Magnesium silicate (pure talc) into sodium silicate (purchased, the 'recipes' found online do not make sodium silicate and involve dangerous preparation). There were no problems with any of the repaired cracks in the 5 months or so I used the burner daily. When I removed the burner, several parts broke again but none along the repaired lines. Incidentally a simple mortar made from lime putty and fine sand works well as a filler for any larger gaps. The geometry of my brick container meant there was a 5-10 mm gap between the two halves of the casting when I installed. I filled these with lime mortar. I also used the lime mortar to bed the door frame onto the front of the casting. Again, when I removed the burner, those lime joints were still perfect. Overall, you're right, a simple concrete with high alumina cement or purchased refractory (which may have added clays in addition to the alumina cement) would make a much stronger casting. The trade off would be the lack of insulation which may increase the time needed to reach the temperatures needed for a clean burn. If you have the broken castings, it's worth considering piecing them together with the cement mentioned as you install. Thanks for posting your feedback, it will be useful for viewers.

Thank you for the reply, and the info, it's encouraging. Did you find that the pieces harden up after firing? I will try piecing it together will the paste your talking about. I really appreciate you taking the time to write such a detailed response. I was pretty discourage when things started falling apart, and this gives me hope I might salvage the pieces. Thanks

@@garyStaple-nt4tl I think it was about as fragile when I removed it as when I installed it (difficult to be certain as I had to break mortar joints from surrounding brick and that may have transferred significant shocks; it did break into several pieces). I think you may be right about the fireclay as I doubt it gets hot enough to fuse and may not allow the cement to fully bind everything. I hope you can salvage something from your project. Good luck!

It's refractory, outlined in the other videos. I don't share your experience of regular concrete, I've cast several fire cores with portland cement and easily get a season's service from them. Cracks are not a problem if the design allows for them.

Thanks Sammy, glad you liked it.

I think your approach would be cheaper and much stronger. I don't remember exact costs but the high alumina cement was expensive and, as there were no local stockists, had significant delivery costs, as did the fireclay (I believe the delivery cost for that was more than the material). The perlite is fairly cheap (I bought a 100 litre bag for £20 recently in the UK from a local supplier) but it considerably weakens the final casting. If you can get ceramic fibre insulation blanket affordably, it would keep the heat in very well, it might just take a little longer for the core to get really hot as the thermal capacity of dense refractory will be higher. All in all I think it would be a good approach. I wouldn't use the clay pebbles again as they are probably a little too large for the thickness of the casting. And I tend to use less and less perlite each time I cast anything to lessen its weakening effect. Denser refractory has the advantage of holding more heat and will stay hotter for longer between re-fuelling. It's only on start from cold where insulated mixes might perform better earlier on in the burn. I believe the cores of the commercial high temperature and ultra-low emissions Pyroclassic burner from New Zealand use dense refractory wrapped in ceramic fibre to good effect. They use a cylindrical casting, wrapped in a layer of ceramic fibre, with an outer thin-sheet steel wrapper. It burns very hot and I think this is an excellent approach. See th-cam.com/video/rb6z-79kW5k/w-d-xo.html - that video contains some good shots of their construction.

Excellent, I look forward to going through them later today. Well done!

I used a lime mortar to bed the core and between the two halves. The proportions were 1 volume of hydrated lime powder to 2 volumes of sand, with about 1/5th volume or ordinary portland cement (this, I think helps set because of introducing clay impurities to the lime rather than because of the normal cement chemistry). I was expecting the lime-mortar joints to break in use and planned to make repairs with purchased fire cement but they didn't break. In fact, when I dismantled the core, the joints were stronger than the casting - the lime mortar stands up very well to the heat (so much so that I'm currently experimenting with lime concrete containing perlite as a casting material, although I can't yet recommend it as it's too early to tell) . Good luck

@@batchrocketproject4720 thanks so much for all the info, it really helps. i have both halves cast and two riser sections and i agree that clay balls do not really help as the vibration juyst makes them float. for the last two riser sections i have used a 50:50 mix of refractory concrete and grog. hopefully this makes the very expensive concrete go further. thanks again for your help. when its done and published ill send you the link. cheers tanc

I installed and used the burner with a large masonry bell for six months, before removing it as it was in a tiny house that I was renovating and took up too much space. It exceeded all my expectations, very warm and a quality of warmth I'd never got from central heating. I did find the castings to be quite fragile and many parts were heavily cracked by the time I assembled it. I've often though that if I was doing the same build again, I might decrease the ratio of perlite and increase the sand to strengthen the casting. I glued broken pieces together using a stiff paste made by mixing ordinary talc (magnesium silicate, not starch based baby powder) with sodium silicate. Once installed, the mended pieces were stable and remained intact when I dismantled the burner six months later. I'm not sure I'd use the clay pebbles again either; they were probably too big for the thickness being case. I think the main advice is not to worry of castings crack when you make them. Just glue them together and stabilise them with whatever surrounding masonry you build.

I've added the mix proportions to the video description. If I was doing it again I might increase the proportion of sand and reduce the perlite content to try and increase the strength as the perlite castings are quite fragile.

The castings were fragile and, as some of my other videos show, many pieces were damaged just by being moved about and temporarily assembling for test burns. When I was ready to install the burner, I repaired the cracked parts with a 'glue' made by mixing ordinary talc (check it's pure talc without corn starch) to a stiff paste with sodium silicate (this is similar to the paste used to repair exhausts, where it is painted on a wrapping bandage). I used the burner daily for six months while I was renovating my house and when I removed it, the glued parts were still intact (and no other crack had appeared). There was no significant heat spawling after six month so I would guess it would last a good deal longer (I removed mine because it was taking up a lot of space in a small house). Incidentally, When I assembled the burner, I used a lime/sand mortar to cement the two halves together and to bed the door frame against the casting. I anticipated that this might flake away in the heat and would patch it with fire cement as problems arose. To my surprise, the lime mortar was intact and strong when I dismantled the burner, it seemed to stand up to the heat very well.

@@batchrocketproject4720 Brilliant. Thanks for that

I've not compared placing the secondary air duct above and below but am happy with the lower option and would use it in future. I don't see any advantage to the top version. For me it simplified the casting and met a personal preference that gases move upwards as they warm.

Thank you for your kind comment Peter. I live in a small house, maybe 700sq feet, built in the mid 1800s, of brick. I installed the heater in coldest room on the ground floor. The room is under 4 x 3 metres and at that time, when I was renovating the house, very draughty. I built a lime-plasterd brick bench and bell sides, with a standard oil drum over the top of the riser. I have a solid concrete floor and don't think a suspended wooden floor would take the weight of what I built. The room had a brick chimney into which I vented the cooled gases from the bottom of the bell bench. The draw was good. It was very big, maybe 1.5 - 2 sq metres footprint , and the top of the drum was only about 0.5 metres below my 2.7 m ceiling, so not ideal in a small room. For this reason alone, I only kept it for one winter. It exceeded my expectations by a long margin. The quality of the warmth was amazing and it was far easier to use and maintain than I ever imagined possible. I burnt mostly waste construction lumber and probably lit it 3 times a day, letting it burn out completely in between. An hour after lighting, the room it was in would reach air temperatures in the mid to high 30s (Celsius) with the wall surfaces averaging about 25˚C (I'm not exageratting, I bought a laser thermometer and was fascinated by it). The ceiling immediately above the drum could reach 70˚C during a strong burn. The stone bench seat would reach around 50˚C (surprisingly comfortable to sit on with a thin cushion). The drum sides would heat to around 200˚C near the top, and around 100˚C near the base. The drum heats up very quickly, you feel radiant heat off the drum within minutes of lighting it. The room upstairs above, would be around 25˚C and the entire house was never below maybe 18˚C even in mid winter. In the morning (I always let it burn out before bed) I was greeted with low 20s ambient temperature in the room where it was housed, and the masonry was still warm to touch. For that whole winter, the only time I used the central heating boiler was if I had house guests staying in the attic room (the other radiator thermostats were turned off). Finding wood was easy as I live in a city with a constant supply of construction lumber from building skips. The only problem I had for that entire winter was the couple of times it became very windy outside, I might get a puff of smoke push out of the secondary air duct. This happened maybe three times in total. The smoke wasn't excessive but did need venting by opening the window (no problem as the room was so warm, drafts became benign). I imagine a modern flue pipe with a rotating cowl would not have this problem. A crack appeared in the masonry immediately above the core which required attention with fresh plaster a couple of times. When I dismantled the heater I discovered poor brcik joints there so I would take more care in the hot areas next time. I miss it but it was simply too large for my house. If I ever move to a larger one, it will be the first thing I install, especially with the way energy prices are going. I'm constantly thinking about developing my original plan, which was to build the heater outside and use it to heat water to supplement my central heating, but never seem to have the time to get on with it. Again, thanks for your comment, and good luck if you embark on a similar project. Dave.

@@batchrocketproject4720 Hi Dave, Thank you for the extensive respons.... Yes the energy prices is what made me go for it. I have been looking at rocket heater build for over 2 years. I like to build a square one out of steel and with a kind of removeble oven to bake bread. Thanks again and have a good one. Peter.

Yes, the secondary air duct is just the square tube along the floor ending at the base of the riser. I thought it might become blocked with ash but find it stays clear provided fuel isn't crammed too close to the back. The overhead alternative may well be better but I found the floor channel easier to incorporate and it seems to work reliably. Thanks for your comment and good luck with your build.

Yes, I installed it indoors as a mass heater for a winter (it was fantastic). I hope to do a follow-up video but I used a brick box with a 200L drum over the riser. The final venting was at floor level through a conventional brick chimney already in the house.

Yes, I made a paste of waterglass and talc and it glued the cracks closed nicely (although I still haven't found the time to make a follow-up video, the repaired pieces lasted a whole winter of daily burns and were fine). Thanks for the comment.

I think the main reason for the weakness it had during the experiments was that the casting absorbed moisture. When I finally installed the burner, there was never any problems with cracks and, although soft, the castings didn't spall or flake. I'm not sure heat made them stronger but it didn't seem to weaken them.

I thought about trying some mesh reinforcement but was worried steel might expand at a different rate to the surrounding mortar and introduce additional stresses under heat (I've read that Coventry cathedral collapsed during the German fire-bomb attacks because the stone pillars had steel inserts that expanded under heat and stressed them). I eventually installed the burner and, once everything was mortared in place, no cracks occurred. Thanks for the comment.

A longer heat riser might indeed increase draw. That said, I followed dimensions from the table here: batchrocket.eu/en/building#dimension which I believe are based on experiments and provide reliable ratios for each dimension based on the diameter of the riser.

Thanks, yes it worked quite well, the glass rarely needed cleaning.

Good question - but I don't know the answer. I suspect that any turbulence will increase the mixing of flue gasses with air and cause a cleaner burn.

According to experiments, the circular pattern is too smooth for effective mixing of the gasses. The design of the port forces the ram's horn pattern for maxim turbulent mixing. see here: batchrocket.eu/en/workings

@@codetech5598 Thanks, I'd forgotten how detailed the stuff on batchrocket.eu is.

I used the following mix, all parts by volume: 2 parts ciment fondu high-alumina cement 2 parts powdered fire clay 1 part fine sand 4 parts perlite 4 parts clay pebbles Mixed with sufficient water to be workable. I would caution against making the mix too dry as the drier the mix, the harder it is to compact it and there is a risk of voids. When I casted the heat riser tube pieces, I was concerned that the clay pebbles might be too large compared to the thickness of the casting and so replaced them with a processed glass product called "growstone". These are smaller than the clay pebbles. I think, being foamed glass, they might melt in the fierce heat of the burn chamber so would use clay pebbles for that. For the heat riser though, the heat is less penetrating and the glass does not seem to have been a problem there.

Thank you for the kind words Sammy. I hope you enjoy building and can tell you I found it all very satisfying even when things go wrong. Regarding wooden plugs, they will work but my early experiments had some disasters as even quite small defects or slightly bad angles make them difficult to release - my advice would be to use multi-part plugs with at least one section that is not in contact with the casting so it can release reliably and loosen the rest (some sort of wedge arrangement). Foam has the great advantage of being slightly compressible and, if needed, can be cut away. Peter's website is indeed fantastic. I'll post the link again here for any readers not yet familiar with it: batchrocket.eu/ I did eventually install the burner as a mass heater and enjoyed my warmest winter ever. I hope to eventually post a follow-up but have been distracted lately. Thanks again for your comment and good luck! Do let me know if you make progress.

A nine inch system must be amazing. I'd originally tinkered with this with a view to building an outdoor water heater that I would use to supplement my central heating. As progress was slow (life events!) I instead installed it indoors as a mass heater and used it for the winter of 2019-2020. I had a bench and a steel drum bell and can honestly say it was amazing; my house had never been as warm and I barely had to use the central heating for a whole season. Sadly, my house is tiny and I was renovating so reluctantly decided to remove it - suffice to say I miss it. I will definitely consider a permanent installation if my next home has room for it.

Thanks Roger. I eventually installed it as a mass heater for the winter of 2019-2020 and hope to report on that soon. I repaired the cracks rather than re-casting pieces and they worked fine when installed.

Thanks for the tip. I used a home made stone glue from sodium silicate, magnesium silicate, and a little fireclay. I repaired the cracks with that and they were fine when I finally installed the burner. After a winter of use, the remained sound. I'll have a look for the Soudal product if I ever get around to another install in future.

You're definitely right on that Richard! Especially if the concrete has perlite or vermiculite as both absorb some moisture even after setting in concrete.

Yes, I eventually installed the burner as a mass heater indoors and used it for a whole winter without problem (2019-2020). Before and during install I cracked some of the castings but repaired them with a paste of magnesium silicate (talc), sodium silicate, and a little fireclay. They remained good for the entire season. When I removed the burner, everything was intact (but parts broke when removing). I've kept the pieces and wouldn't hesitate to repair them for a fresh install when I get the chance.

vea otros videos para materiales y métodos. Gracias por tu comentario.

Much of what looks like smoke coming from the outside of the burn chamber is actually steam caused by the casting getting rained on. You're definitely right that the efficiency depends on the gaps being sealed. I eventually installed the burner and closed all the gaps with mortar and there were no further problems or cracks. Thanks for the comment.

Mine didn't have that but yes, I've seen videos that guide the burn into a nice vortex. We definitely need to experiment to see if the direction of the swirl changes either side of the equator!

The coriolis force is BS. Is been proven nonsense many times

Sorry for the delay in replying Lance. I bought the high-alumina cement and fireclay from a pottery supply company, via the internet at www.bathpotters.co.uk/ I bought perlite and the clay pebbles from a hydroponics supplier - www.hydrohobby.co.uk/. Hope that helps.

In real use, the riser would be inside a 'bell' made of a drum or masonry (in order to catch heat) so the sparks would be arrested there. Have a look here for examples: batchrocket.eu/en/applications. I'd have to check my notes for weights of wood and burn times.

Yes, many designs use metal. I preferred to experiment with concrete as, for me, it was easier and cheaper. Thanks for the comment!