Heating The Greenhouse Rocket-Style… The Adventure Continues

 In Alternative Fuels, Built Environment, Design, Featured, Gardening, Greenhouse, Permaculture Projects, Retrofit

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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: http://www.woodheat.org/wind-chimney.html

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
      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
      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 http://www.dirtcraft.ca for more info. They are living out near you now!

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