We can heat our well insulated 900sqft of living space to 65-70°f using around 2 cords of wood each year with our Rocket Mass Heater. We typically wake up to 65°f and burn a fire in the morning and another fire in the evening. A "J" tube burn chamber covered by a 55gal barrel creates radiant heat as well as a thermal pump which forces exhaust gasses horizontally though ducting in a large box filled with pea gravel. The gravel extracts most of the heat from the exhaust radiating it out slowly after the fire burns out. By the time the exhaust reaches the chimney it's 120-200°f down from 300-500°f at the barrel. The combustion is nearly total so very little smoke is exhausted and maximum BTUs are used to heat the space. Built with materials found at most big box hardware stores Rocket Mass Heaters are cheap to build, easy to source, and incredibly efficient. It is the favorite contraption I've built on the homestead.

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Colder temperatures have arrived here at the homestead so it's time to start posting about my rocket mass heater again. This is the most efficient wood burning heater for the cost and ease of construction you will find. It paid for itself in energy savings the first winter. Plus, since it burns so little wood I save tons of time by not having to gather, split, and stack cords and cords of wood. #homesteading #permaculture #permies #meshtadel #rocketmassheater #woodburner #rmh View quoted note →
Oh wow that’s a really clever way to store a ton of the heat for longer. Never thought of that, just running the chimney horizontally through a long track of rock. Cool setup 👏🏻
Thanks, it was pretty simple to build and really cheap. Plus all the materials were easy to find. No special tools needed. The most expensive and difficult to install component was the 8in stainless steel chimney liner. I needed some help from another person to install it. I chose to do pea gravel in case it didn't work well or I decided to remove it in the future. Cob would work even better and we would probably burn much less wood. Cob is a lot more permanent though. If I build another one I am confident enough to build it with cob.
I don't have a wood stove. I chose to put the RMH in close proximity to the chimney. I basically wanted to heat my house with wood in the cheapest, easiest, most efficient way possible. So I built the RMH core next to chimney and made a tall stack bench/mass at counter height vs a sitting bench. This saved floor space in the room. Basically taller skinnier mass vs short and wide. This way it all fit nicely in the room and I didn't have to do anything complicated. I could just use the chimney I already had from the existing fireplace.
Otis Bitmeyer's avatar
Otis Bitmeyer 2 years ago
I love RMHs. Well done! I’ve wondered about integrating an asic or two into a RMH as a way to capture heat from solar powered ASICS during the day and store it for nighttime use. It might be more efficient to run immersion and capture heat into a big water tank, but the simplicity of storing heat in solid mass intrigues me. Do you have any thoughts on that idea?
I don't see why it wouldn't work, instead of the core of the RMH replace with solar powed Asics, instead of venting outside vent to a location where you need heat the most and let the mass release some heat at night when the asics aren't running. For it to be effective, you would need to generate more heat than you needed during the day and figure out how to charge the mass with it.
RAnger's avatar
RAnger 2 years ago
Perhaps two independent chimneys. While traditional rms must push through the thermal mass and vent out of the home, the asic miner would push through the thermal mass and back into the the home.
Jim's avatar
Jim 2 years ago
Damn man...you have all the cool permie stuff! Looks nice as well. Glad to hear its working well. There was a company working on a commercial unit a few years back, not sure if they ever got that off the ground or not. I was interested but never heard much about it after I signed up for their email alerts.
The rocket mass heater is definitely the real deal. Easily the most bang for the buck out of anything I've built. It's been working flawlessly for years now. I have to vacuum out the ash once a year and I do sweep the chimney but honestly I don't think its ever really been necessary. The most creosote build up I've seen was maybe 1/16-1/8in on an 8in chimney. Plus the exhaust gas is never hot enough to ignite it. I burn some punky ass wood in there too. I upgraded the insulation on the riser and rebuilt the burn chamber at the same time. A few of the fire bricks cracked, I think because I was burning it too hot at first. It really is a fantastic technology that anyone with the right situation to have one, should. When it comes to manufacturing RMH, the core could be done but the mass probably has to be custom built. The core isn't really hard to build anyway and it's much more forgiving than the books make it out to be in my experience.
Otis Bitmeyer's avatar
Otis Bitmeyer 2 years ago
Yes! I’d definitely want to be able to also burn wood. Love this.
Now that transaction fee storm has passed I'm back to heating my living space primarily with wood in a rocket mass heater instead of Asics. Wood is burned in the small firebox and heat radiates from the barrel warming the space quickly while the fire burns. image As the exhaust gasses make their way to the chimney, they pass through ductwork in a plywood box filled with pea gravel. image The majority of the heat from the exhaust is transfered to the gravel before exiting up the chimney. By the time the gases exit the box, they are cool enough for me to put my hand on the chimney pipe. image After the fire burns out, the heat absorbed by the pea gravel slowly radiates out into the living space until the next fire is burned and the gravel is recharged with heat once again. I built this rocket mass heater for a fraction of the cost of a wood burning insert, with no special tools, materials, or skills. image It has been an unusually warm November and December here at the homestead. Normally we have to start burning wood in the rocket mass heater early November to stay comfortable but this year, the bitcoin mining dehydrator was enough to stay warm and do some food preservation simultaneously. Transaction fees started climbing and I was shocked to see the most efficient miner I had approaching break even at my electric rate. I didn't have the circuit to run it wired yet but this bump in fees was the motivation I needed to get the miner hashing. Coincidentally, the weather also started to get colder finally so getting the miner up and running was a win/win. image It successfully kept us and our guests warm through the holidays, even earning some Bitcoin beyond the cost of power at times, all while allowing us to save our firewood. image We did have to fire up the rocket mass heater a handful of times, but so far we've burned less than half the amount of wood compared to previous years. This is thanks to the combination of the warm weather, and high transaction fees allowing us to stay warm with heavily subsidized electric heat. image This might be the first winter we make it through with wood leftover for the next year, typically I'm scrounging for the last couple weeks. #permaculture #permies #homesteading #selfsovereignty #meshtadel #rocketmassheater #woodburner #bitcoin #bitcoinmining #plebminer #rmh #grownostr View quoted note →
It took a few weeks, I built the core outside first, tested it, dismantled it, rebuilt it inside, tested it, built the ductwork, tested it, too it apart, built the box and rebuilt the ductwork, filled it with gravel (this was the most labor intensive part, took a friend and I several hours hauling gravel), then I made the finishing stuff so it was more of a process than a self contained project.
This is really inspiring! I’ve been a fan of Rocket Mass Heaters for years, but have never built one. Now that we have a citadel/homestead in Colorado, that can be a possibility. I’m curious, do you run the heat from your miners through the same ductwork as the RMH? It looks like it might be from the picture.
No, my miner heating situation is much less sophisticated, I just point the exhaust from the miner in the direction I want the heat. Sometimes into my furnace ductwork, sometimes directly into the room. There was some discussion around using the miners to heat mass during the day running on solar to take advantage of the heat at night while the miner was shut down. That is an interesting concept. I'm thinking the best way to store heat from a miner would be in water not cob or concrete.