Rocket Mass Heater Failure

The folks at Mud Dome blog couldn't get their rocket mass heater to work in Canada.
The folks at Mud Dome blog couldn’t get their rocket mass heater to work in Canada.

I love rocket stoves and mass heaters and have been recommending them for years. However, there are limitations to everything. Here’s a report from frigid Canada where a rocket mass heater wouldn’t work.

“Our adventure in natural building and sustainable living has hit a major hurdle. A big part of our plan was the Rocket Mass Heater. It really seemed like a good idea at the time. And I really wanted it to work. I wanted so bad to love it. Never got there. I built a few mockups and rebuilt the final one twice. I read everything I could find on the subject, ran all kinds of experiments and even traveled to Oregon to meet the folks who are the most experienced experts in the world on the subject, including the original inventor.

Things worked great if conditions were right, but wind is certainly an issue and we get plenty of that here. In order to get a decent draw I had to have a tall chimney out side. That means a heavy column of cold air is pushing down into the system. Since a RMH isn’t sealed, cold air blows through the system and into the house making it very difficult to get a fire started. I tried warming the pipe with bricks from the cook stove, candles, and even a torch. Putting a duct fan inline at the top of the chimney helped for a couple days, but once the system got hot, it burned out. Getting it going in very cold windy weather always had the risk of having smoke blow back into the house. Not good, remember that ‘look’ I mentioned? Besides, even when the damn thing was burning great, with that cool rocket sound, I’d have to feed it every 3-1/2 minutes. My wife and I talked about all kinds of modifications but in the end we’d never be able to make it work in our situation and environment. You can put wheels on a horse and shove an engine up it’s ass and you still won’t be able to take it out on the highway. So goodbye rocket crap heater and hello Blazeking Princess wood stove.”

MudDome blog

21 thoughts on “Rocket Mass Heater Failure”

  1. Fault was placing the draft fan online with waste glasses. Better to have a fan in parallel cold leg into a Y that as the air moves it pulls the fumes up like a venturini effect…

  2. Try putting a freely pivoting venturi windvane on top of the chimney. There is a company in Australia that makes them as ceiling cooling devices. It should always suck the air out then and actually assist the rocket’s dynamic.

  3. When they work, they are awesome.
    When they don’t, you wanna get some fresh air even if it is well below 0.

  4. It took a few rebuilds, increasing the heat riser each time, before I was satisfied, and I had previously built 2 no problem. I reckoned the lower air density at my 8000 elevation was the obstacle not the cold, but we only get down to -20F.
    There are a lot of factors at play to consider if you want to build your own stove efficiently and effectively. They aren’t for every situation. But as a tree climber, I like filing my removable hopper with chips, which is nice fodder for these. Also, it sure addresses the couch question in a dome, if you go the bench route.
    Since we are all speculating here on diagnosis: if all the brickwork was insulated well, they had a 4.5′ riser, and no bottlenecks, then either insulating the chimney if external, going 7″ to 8″, shit 10″ maybe by looking at their blog pix, and better fuel might have done it. Things become a touchy balancing act at that level of efficiency.

  5. The only solution I can think of this would be using a tesla valve in the chimney to prevent air from entering, but then the cleaning of the creosote becomes very difficult.

  6. ‘Muddome’is a dude. “She” is his better half who writes a much more interesting blog at
    The truth is that cold air can enter a properly built rocket mass heater. (Yes, I read everything about RMH at permies, and also at the more advanced forum for rocket stoves at I see so many posts and comments from people who insist that rocket mass heaters are the absolute best thing ever developed. (You see the same religous ferver around earthships.) Usually these folks are persons who have never actually seen, let alone built one, but saw it on the internet. I still love rocket stove tech and will probably keep experimenting in my shop, outdoor kitchen, etc., but would never again put one in my home unless I were to move to a milder climate. My setup had no restrictions, I checked that first. My heat riser was 4.5 ft tall. The overall system was a 7″ diameter. The reality is that the system worked just great under most conditions. However at 40 below or worse, I experienced serious problems. Some people may never experience this depending on where they live. At these temps, we’re talking life or death not just “it’s a little chilly”. The draft created by the heat riser will only push the gases so far. An external chimney is still required if there is to be any length of run through the mass. It’s a balancing act.

  7. I’d like to see a sketch or diagram of how they set theirs up. It’s easy to make a mistake in RMH design, making a bottle neck, or a short heat riser or something similar. But, once you get those components right, it’s hard to go wrong.

    I know there is a huge community of RMH builders in cold climates that love their RMHs, but many have tweaked and perfected their version for a while before employing it as the sole heat source for the home.

  8. It seems to me that the Rocket Mass Heater design just couldn’t put out enough initial heat to get the chimney up to temp in such a cold & windy environment. Maybe it could work if 2 stoves were attached to one chimney, with a traditional stove used first to get that blast of heat to warm the chimney & create proper draft? Of course, that solution just might not be worth the effort . . .

    For such climates, I think an efficient traditional stove couple with a secondary fire-gas combustion unit on the stove-pipe might be the optimum solution.

    I wouldn’t necessarily call this a technology failure, but instead the wrong tech for a particular climate. It reminds me of people being disappointed at evaporation cooling or evaporation refrigeration “failing” in a humid climate . . .

    • Yes, good point. It may not be a failure, just a limitation in the design. That’s why I published the story. Lots of readers live in cold climates and so it would be good to know what’s going on.

  9. The RMH forum at is the best place to discuss RMH issues. I bet those folks could help troubleshoot and offer some constructive suggestions.

    • They’re smart and resourceful as you can see by what they’ve done on their blog. The RMH was obviously very important to them since it was going to be their main heat source in Canada. They wouldn’t easily give up. It seems like they would have checked out a forum such as the one you mention to troubleshoot the situation. This is a puzzle. Maybe I’ll email them for input.

      Someone wondered if I’m promoting BlazeKing Stoves. Get real. I’ve never even heard of them.

  10. I also live in a cold windy part of Michigan. How cold has anyone used the RMH successfully? It got to -25F last winter and my heat was expensive. Anyone had success in similar conditions?

    • Let’s see if we get some dialogue going here to figure out what happened. Abe has already chimed in. Anyone else live in a really cold climate and have build these?

  11. if her draft was dependent on the size of her outdoor chimney, she was doing it wrong. Draft, in a rocket design, is driven by the height of the heat riser, and I suspect it wasn’t tall enough (should be 3ft or more). Also, there could have been a restriction somewhere preventing good air movement through the system.

    There is no way cold air could enter the house through a properly built RMH, the serpentine heat exchanger just won’t allow it, and the heat riser would work against a cold influx of air.

    So, I suspect this wasn’t really a case of an RMH not working and more of a case of a poorly implemented RMH design.

    • Let’s hope they respond. They said they researched it thoroughly. They even went to Oregon to talk to Ianto Evans I believe. But maybe they made a mistake.


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