Brief setting... In april I will lay an aircete slap, on top I will place a 20×32 military tent in which my experimental RMH will come to life. I am designing for effiecientcy all around including space, fuel, labor, materials and to easily disassemble, modify and fine tune. First question. Can aircrete be used in the fire box? All my other questions are on this simplified drawing of many other drawings. The lower two questions are in the bell FYI. The thermal mass wrap around bench is not shown in first image. First image is most accurate and useful. you can ignore writing on other images. Thanks for reading!
Greetings Willy and welcome to the Rocket Scientist Central HQ
I see from your sketches that you have been having lots of great musings over designing your dream dragon.....certainly something the folks here can help you out with making it a reality.
In regards to aircrete, if you are going to be using regular portland cement as the binding agent, it was never designed to withstand the extreme heat generated by a RMH, in particular as a core material.
The moisture in the cement will soon be sucked right out of it and will quickly start to spall and crumble.
Perhaps it could be used as a foundation material outside of the core to help keep the heat transferring down into your floor but even then, its longevity is not guaranteed.
There are much better materials out there that can be used as insulation that work very well and have been proven over time by many people.
Light insulated fire brick, Dense firebrick, ceramic fiber board and ceramic fiber blanket are the most common choices.
If you wanted to experiment with aircrete, it would be a great way to get a core all built in your backyard and see how it performs before committing to anything. This is a step many people ignore and want to just go with a full in-house installation that they expect to work flawlessly and last for generations. This to me was one of the most memorable moments for me in becoming a rocket scientist and one I'm glad I never cheated myself out of having.
I believe most people don't make a bell like that because the exhaust doesn't typically like to go below the j-tube. A chimney with a strong enough draft would help, but it looks like you are not using any chimney? I would be afraid you will get a lot of smokeback if I read the drawings correctly.
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Thanks for the warm welcome Gerry. I intend to do a lot of experimentation and really appreciate the motivation. OK great info sounds like fire bricks may work better for me then. maybe the aircrete could hold up better with a layer of something else the "heat riser" as I think it's called (the thick shaded insulated pipe that connects to fire Box) is a major component im trying to figure out.16 gallon drums would be good size but would burn up maybe if I insulated the The inside pipe with the ceramic fibre blanket you mentioned? The foundation will hopefully be a hard faced aircrete.
So Jordan i should Lower the J tube with wood hole at ground level and J tube level with exhaust entranchere. Does This earlier drawings with J tube underneath the exhaust show a better option as to your point? I Hope im understanding you right. I've heard of Priming spots but don't fully understand them I've shown an idea for the prime spot in picture 4 . This would help for cold start right ?
The heat riser is a very simple thing. Perhaps the easiest and hardy heat risers you can make has been dubbed a 5 minute riser.
5 minute riser
Your pictures are a bit confusing that stray away from the basic outline a typical J tube RMH generally follows with complexities that may not work very well.
Have you seen a copy of The Rocket Mass Heaters Builders Guide or Rocket Mass Heaters Superefficient Woodstoves YOU Can Build ?
In them, they give brick layouts for J tubes and go into much depth into how to build them. They can answer all sorts of questions and get you going with proven designs that work.
Max has the critical factors laid out. Many configurations have been tried by experimenters with professional testing instruments, and there is one basic design that works best. Coincidentally, it is also about the simplest design - pretty much all square corners and straight lines.
You DO NOT want the exhaust pipe going up through the heat riser as the earlier drawings seem to show; that would kill the efficiency of combustion and give you all sorts of problems. You do not want the exhaust coupled too tightly to the side of the riser either. You want it to come from near the bottom of the bell cavity, mostly insulated, maybe near the exterior of the bell depending on how much heat you are extracting in the bell and how much draft assistance you need, if any.
Thanks for all the feedback everyone. I'll be getting a guide as soon as I can. It was fun to design anyways and maybe I'll still toy around with similar concepts after I build a trusted one to keep me warm! Thanks again everyone, this is the first ever forum I've made anywhere and yall have helped me see the importance of em!
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