4 Comments to “The Rocket Mass Heater: How Heavy Is It?”

  1. fred

    Dec 29th, 2010

    I would add a bit more to that weight according to a web site visited sand compacted weight about 105pound per cubic foot and 95pound for dry earth! so I would add a good 25% to your weight estimate!

    By how is the stove working for you so far? how log do you burn to get decent heat? How do you get the ash out, it seem like in front you have a trap for it, but it look like it is below the floor level?

    anyway always a pleasure to read your progress.

  2. Chris

    Dec 31st, 2010

    I think my numbers are still good … I measured the volumes of sand and dirt loaded into the bucket of our backhoe. We screen this material as it goes into the bucket so it is definitely not compacted at this point!

    To date we have not had a lot of experience with the stove. We did some day long burns while we were drying the stove out. We got most of the moisture out of the cob, but it still needs some more drying.

    The bench warmed up to the point that it was impossible to sit on it for extended periods of time. We still need to add cob to the top of the bench to give us 6″ of cob between the top of the pipe and the top of the bench. The extra cob should spread the heat at the top of the bench to a comfortable level … we will see!

    If the stove is completely cold it takes a bit of work to re-light it and get it drafting properly … not unlike a masonry stove. If the stove is still warm it lights up right away … again like a masonry stove. (If the stove was lit the previous day there seems to be no problem starting it in the morning).

    When we had the stove lit for a couple of days we saw the temperature in the earthship slowly go up. We got it up to around 10 degrees C from an average of 3 degrees C. However, an earthship is all about thermal mass and I think it is going to take a bit more time to get all that mass a little warmer …

  3. Yvan Pelletier

    Jan 4th, 2011

    Your estimate for the mass is probably good. My rocket mass has 27 feet of duct and my estimate of the mass was around 5 to 6 metric tons.

    For your hope that the wall next to the RMH might store some of that heat. From my own experience, over 11 inches of cob around the pipe, you don’t feel that much heat. Of course, if the heat has no where else to go, in the long run it will be warmer over 11 inches of cob. In a earthship like yours, a RMH will surely help to keep the eat in your walls.

    About your problem to light up the stove. We had those same problem here in the first two months of operation. I think, it’s mostely because of the moisture. After those two month we rarely had problem, and when we had some it was because it was to warm and humid outside (over 10 degrees C).

  4. Chris

    Jan 6th, 2011

    We are noticing the same thing … it is getting easier to light.


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