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The Rocket at the end of day two

The Rocket Mass Heater is now functionally done. After installing a proper chimney, it really hums!

I have now fired it four times for about an hour to an hour and a half to drive off any remaining moisture in the cob (I should have done this months ago) and the bench is just starting to show signs that it is retaining heat. Once the greenhouse is completely sealed up with thermal curtains* installed we will be testing the rocket to see how long the thermally charged mass bench will keep the greenhouse above freezing. If we are successful we will be working in the greenhouse as early as March this year without fossil fuels to keep the space warm.

Initially the rocket was not functioning properly because the chimney was not tall enough. When a chimney is placed around a building, all sorts of strange low and high pressure zones form around the structure due to wind blowing the building from various directions. For this reason the rule of thumb is to project the chimney at least 2 ft. above all surfaces (usually roofs) within a 12ft radius. It is also advisable to have a high wind cap which ensures that no mater where the wind is coming from there is always proper draw from the fire. Here is a great explanation of chimneys and high wind caps:

Rob and Ashley looking pretty pleased about the project!

The last remaining step to complete the rocket is a render coat which we will apply once we have warmer conditions. The render coat is simply a protective layer with a finer finish applied to the outside of the cob bench to increase its durability.

*Thermal curtains are used inside the greenhouse along the glazing to reduce heat loss at night. They can be bought commercially, or you can use any insultative material, for example a blanket or construction tarp.

Below is a video that we produced showcasing the construction of the rocket mass heater.

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Showing 32 comments
  • Mic

    Great video and website Rob!
    I’m considering a smaller rocket mass heater for my greenhouse. I was thinking of running the flu pipe under the raised garden bed. What kind of temps are you getting from your thermal mass? My raised bed is 12 to 15 feet long by 2.5 high and wide. I’m looking to warm about 1000cubic feet. I’m looking forward to your input and suggestions.
    Thanks, Mic

    • Rob Avis

      I am not sure if this is a good idea. Water infiltration and vitrification of your soil are both potential issues. Consider storing heat in something else.

  • Jackie


    I am in Penticton, BC Canada. I know the regulations will vary from province to province and town to town, for that matter,but I am wondering how the permit process for this project went and how your homeowners insurance regards to the building and use of the rocket stove. I am hoping to have some arguments and arsenal in my back pocket for my own project.



    • Rob Avis


      We had no issue with the greenhouse. Regarding the rocket you should look into the code for massonry heaters. The whole unit is totally fire proof so there is little to know risk. I would contact Ashley and Heather from for more info. They are living out near you now!

  • Thomas Russell

    Thanks for all the advice however I am going to tear it down and try to start over as I cannot get the smoke to go outside it backdrafts into my green house. Horizontal pipe is about 30 feet horizontal then straight up and out the top of the greenhouse with a cap. still no luck.

    Bought a double barrel stove hooked it up it works just was given 2 100 pound propane tanks will follow a video on utube and make up to three of these units. Then I hope I can heat for about 10 to 11 months of the year.
    Thanks to all that responded I could not answer before now as I have been fighting cancer and just got the all clear a week ago I do not have to visit any more hospitals or clinics. So now I want to do a little work each day to try to rebuild my muscles and some strength as I am very weak

  • salvador

    I’m in Mexico and perlite is non existent. Is there something else I can use insted of perlite?

    • Rob Avis

      Yes, you can use ash or zonalight for the insulation in the heat riser.



  • George

    Thanks for the reply. Do you know of any suppliers of refractory brick in the Edmonton area?

  • george

    great video guys. I’ve seen some that use fire clay instead of refracted brick. Would this method give the same result??

    • Rob Avis

      Yes, however the clay brick would not last as long and, would not insulate as well which is important to its opperation!

  • Peter

    To Thomas,

    The best thing to do is put some 3/4″ vertical strips of wood on the flamible material and cover it with a tin sheet (the kind used for roofing. This provides an air space behjnd the tin which disperses the heat. Also the tin roofing will not burn.

  • Mary

    This is GREAT! We are in Edmonton and looking at living a bit further north. We are thinking of combining this with the underground gardening idea, though it is a bit tempting to include this in a cob constructed house.

  • Thomas Russell

    Please use the email I have listed as it is more convenient to use than this computer which does not work 1/2 the time.
    I am Thomas Russell dam near 70 and am fighting cancer at present.
    I have built a rocket stove in my greenhouse and it is within 6 inches of the UV poly and the laminated gothic arch beams . How do I protect the same for the intense heat put off from this barrel I am using refectory concrete so I know that will absorb a lot of the heat but I cannot afford a fire hazard . Can you help me

    • Rob Avis

      Thomas, I will need more information but my gut tells me either move the barrel well away or put something other than a flamable material near it.

  • Carter Murtaugh

    Greetings from Florida! I’m bored to tears at work so I decided to browse your site on my iphone during lunch break. I really like the information you provide here and can’t wait to take a look when I get home.

  • Kenneth C Young

    I love your idea of these Rocket Stoves.I was wondering as in the video you have via the link below could a Rocket Stove be build with the idea of having a thermostatic control system taking heat from for example the bench storage whenever needed,you have set up which joins the Rocket Stove.

    There would be for example in my case a duct system leading from the Rocket Stove bench storage area which would be in an insulated outside shed to my trailer where I could use a thermostat to adjust the amount of heat that I would want in the trailer.

    Here is the link…

    Hope that this could be worked.

    Kenneth C Young

    • Rob Avis

      Thanks for the comment. Yes you could set up a termostat. If you built an insulated shroud with an operable duct on the bottom and top of the shroud you could charge the bench and then have the duct open on the top and bottom as heat was needed in the room. Good idea.


  • Bill Greene

    I am building a greenhouse this summer and would love to build a rocket stove for it. Could I get some drawings or measurements on your design?

    • Michelle Avis

      Bill, the best resource for plans comes from two places. 1) The Rocket Mass Heater Book Written by Ianto Evans ( and from our friends at the Dartfield Earthship in British Columbia. The folks at Dartfield have done a masterful job writing and easy to follow manual on how to build and design one of these beauties. They also have a set of plans for sale as well. You can tell that they are engineers, I mean that as a compliment!

  • John

    Great video! One question: Why is the barrel not also insulated with earth? Seems like it would just add more mass for the heat to be stored in and the barrel stack would not get so hot to the touch. Could you please explain this? Thanks!

    • Michelle Avis

      John, Thanks for your comment, Rob Avis here. The barrel is best left mostly exposed for a couple of reasons. 1) This is when the system transitions to a low pressure system. As the gases pass over the heat riser into the barrel the heat radiated from the barrel reduces the temperature of the combustion gases thus shrinking them and helping creating the pull that keeps the draught going. 2) The barrel provides quick heating to the room where as the bench provides long term heat release. If the barrel was covered with cob the heat would take much longer to release which may make the room uncomfortably cold for longer. The integration of the quick and long term heat is what makes the rocket mass heater so unique and different from a conventional wood stove. Thanks for the comment.

  • Tanner

    Great video, very interesting and informative! Especially liked the continuous video of construction and the joke at the end 😛 hope you’re both doing well!

  • Dustin Bajer

    Great video Verge and DirtyCraft!

  • Mary

    Very impressive! What square footage is there in the greenhouse, and is it open into anything else? From the looks of the movie it is attached to the side of another building. Sorry, I haven’t done my homework, where are you located? Just wondering how far north this will work. Thanks again!

  • Martin Reinhard

    Hey guys this looks good, What You guys need is a Mr. quick split from www. can order it online. It was featured on the Dragon’s den December 5, 2012.
    This kindling maker is ideal to make small pieces of wood for your rocket stove.
    I took a class with Ashley on Heather last year
    cheers Martin

  • Andrea

    Love it!! Simple natural heat exchanger =)

  • Hart Wichern

    Thanks for posting this. Is it possible to draw exterior air to feed the rocket. As it is designed at present…while the rocket is burning,a lot of the interior heat is drawn into the rocket.

    • Michelle Avis

      Yes it is possible and it simply requires running a duct into the top end of the feed tube. We did this in a different RMH that we installed last year and it works great.

  • Joey Hundert

    This is really great guys!

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