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Rocket mass heaters
  • Vote Up0Vote Down
    January 2012
    I think this would make a great project. You don't get more essential of a need than heat, and a rocket mass heater is a great way to heat stuff. It's supposed to use 1/5th less wood than a woodstove, and you can use tree trimmings instead of actual trees.

    It's not super complicated either, a few optimal designs just need to be documented with with construction details. I'm invisioning a portable one where you've got 4" thick concrete sections with holes in them. When connected together, these sections create the snaking channel for smoke to escape. Mass Heaters.pdf


    We have been asked to remove some (but not all - very gracious of them) of the author's work and we are complying. He/She does excellent work and I recommend clicking through to their site.

    Below is just a taste!

    rocket mass heaters in a nutshell:
    heat your home with 80% to 90% less wood
    exhaust is nearly pure steam and CO2 (a little smoke at the beginning)
    the heat from one fire can last for days
    you can build one in a day and half
    folks have built them spending less than $20

    the verbose details on rocket mass heaters:

    This could be the cleanest and most sustainable way to heat a conventional home. Some people have reported that they heat their home with nothing more than the dead branches that fall off the trees in their yard. And they burn so clean, that a lot of sneaky people are using them illegally, in cities, without detection. When somebody first told me about rocket mass heaters, none of it made sense. The fire burns sideways? No smoke? If a conventional wood stove is 75% efficient, doesn't that mean the most wood you could possibly save is something like 25%? How do you have a big hole right over the fire and not have the house fill with smoke? I was skeptical. And then I saw one in action. The fire really does burn sideways. The exhaust is near room temperature - and very clean. The smoke doesn't come back up because a huge amount of air is getting sucked into the wood hole. Neat! I sat on one that had not had a fire in it for 24 hours - it was still hot!

    how it works:

  • 9 Comments sorted by
  • Vote Up0Vote Down
    January 2012
    Rocket stoves have been around for awhile. There is a guy on YouTube names Apostal who has made significant advances in the rocket design. I also have a rocket stove oven design that was released by a NGO in Uganda.

    If you want the NGO PDF file let me know. I offered it before to the group but never heard anything back.
  • Vote Up0Vote Down
    January 2012
    I would like to see a professional grade version of a rocket heater using stainless with an enclosed welded wood feed -> Combustion chamber -> exhaust vent (thermal mass). I have Ianto Evans book and the one concern in it that concerns me is the lack of airtight sealing in the whole assembly. Having work quite a lot with cob I know that it has a tendency to crack while drying. The concern in the book is that if there are cracks in the sealing clay or cob it could create a CO/CO2 leak into the house. For this reason I decided not to install the racket stove into the cob building I made.

    I think the issue could easily be solved if you were to have the combustion chamber and wood feed welded together, instead of using cob. Then simply run the duct with professional sealant through whatever thermal you like. If a standard model could be made it may be easier to get it passed into building code as well.
  • Vote Up0Vote Down
    January 2012
    I'm interested in the pdf.
  • Vote Up0Vote Down
    January 2012 here is the link to the oven. We can use the CEB blocks, do some building and documentation. Knock this one out in a week at FeF....
  • Vote Up0Vote Down
    January 2012
    Thank you Metz
  • Very nice Metz. 

    I wonder though, will CEB's stand up to the high heat environment or is this a case where fired bricks are a necessity?  I would be concerned that CEB's might lose integrity and the whole thing could collapse.  Also possible I am worried about nothing.  It would be worth it to test first though, exposing the CEB's to high heat from one direction, some on the narrow side, some on the broad side, and see what happens to the bricks.
  • Vote Up0Vote Down
    January 2012
    It the CEB was made from a clay sand subsoil, and thoroughly dry, there should be no issues. The design has been extensively tested and documented already in the PDF link.
  • Oh believe me.  I read the PDF.. and saved it locally.  I am very interested in this. 
    It specifies kiln fired bricks.  It addresses issues in the prototyping phase of breakdowns due to high heat (in metal components).  Switching from kiln-fired bricks to raw, dried CEBs introduces a variable they did not test.

    You might be right.. there might be no issues but that should be confirmed for safety's sake.
  • Kind of an essential basic technology, like a scythe for tall grass or chainsaw for cutting wood. I'd say:
    - You can fudge the materials at every step of the way
    - Certainly no need for high-density firebrick at any point in the design
    - Design for rebuilding every few years, but don't be surprised when you don't have to
    - If you're thinking thoughts like "stainless steel" then you are working way outside the DIY/bootstrapper realm, that stuff costs major cash -- think more like scrap galvanized or ceramic pipe or tiles
    - CEB/cob works just fine, don't nitpick, just do it, you'll see
    - Have you ever used a normal cast iron woodstove? Don't worry about CO/CO2 leaks, just pack more cob in the cracks if it bugs you, we're not designing a clean-room furnace here, we're designing an order-of-magnitude-better woodburner for under $20.
    - Fuel type for the sort of rocket mass heaters you see in these videos is long thin pole wood, bark and all -- perfect for coppice/brush situations, sidesteps the equipment, maintenance, time, skill, and tree stock that cordwood-based heat demands, get to use the whole top of a felled tree and not just the thick stuff.

    Here's the related "masonry furnace":

    This is my favorite, I built a working mock-up of it last year:

    Bricks kind of fall along a spectrum of insulation value -- from highest (lightweight air/vermiculite filled bricks -- loose ashes are also insulating) to common bricks to low-insulating refractory-grade brick (high thermal mass and will not spall/crumble under repeated high heat fluctuations, but both expensive to buy and DIY). The lighter-colored, sharp edged, odd-shaped units used in the cores of a lot of these heaters are refractory "fire bricks". Because I can make lightweight "insulating" sawdust bricks and don't mind rebuilding the furnace core every few years, don't have to use expensive refractory.

    I made a bid for a friend on this subject last year:

    == Masonry Heater ==

    $20 - wheel barrow, chutes and ladders
    $10 - brick tools
    $10 to $100 - pile of common bricks
    $10 to $1000 - pile of fire bricks (not necessary, only if they can be
    found for near-free)
    $30 - few dozen insulating bricks (made custom in pit kiln)
    $20 - huge pile of clay
    $20 - mortar-grade clay
    $20 - lime mortar
    $20 - sheet metal, barrels, ducts, cast iron
    $20 - metalworking tools
    $10 to $200 - full heating season of wood fuel

    Scrapper Total = $180

    Ballpark (way high) labor hours, two people working at same time:
    40 hours - collect bricks
    20 hours - collect wood
    20 hours - odds-n-ends
    20 hours - setup time
    20 hours - build furnace
    Total = 240 human-hours

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