Our Rocket Stove

 
  • Editor’s note: we have a new design for a portable rocket stove here.

Low-tech is the new high-tech, and the best example of the low-tech revolution is the miraculous rocket stove–a stove that makes it possible to cook with small twigs–no logs needed! Best of all rocket stoves are easy to build. We liked the idea so much that we decided to build a permanent one just off our back deck for entertaining and as a backup to our gas stove should an emergency take out our utilities.

The rocket stove was developed for use in poor nations where wood used for cooking has led to the vast, wholesale, deforestation of large swaths of the earth’s surface. Rocket stoves can be built out of metal or masonry and consist of a L shaped tube, at the bottom of which you place your wood. The chimney effect creates a highly efficient, largely smoke-free burn. There’s no need to cut down a tree to cook your dinner–all you need is a few small branches or twigs.

Before we built the rocket stove we considered making a cob oven, a mud domed wood fired oven in which you can cook bread and pizza. There’s a trend in the eco-world to build cob ovens and we felt a certain pressure to keep up with the eco-Joneses. We started to build the base for one and then began to think about how often we would actually build a fire, especially considering that it has to burn for several hours before a cob oven gets hot enough to cook in. Also, where would we get the logs? And how good is it to burn such a fire and contribute to Los Angeles’ already smog choked air?

Staring at the bricks we had scavenged to build the base of cob oven, we realized that we could re-purpose them for a permanent backyard rocket stove that we would actually use. Furthermore we realized that our rocket stove could burn some of the palm fronds that regularly tumble down from the iconic palm trees that line our old L.A. street.

Here’s the materials we used:

36 bricks
4-inch galvanized steel stove pipe elbow
4-inch stove pipe
ash (scavenged from park BBQs)
1 tin can
50 pound bag of premixed concrete for the base
mortar mix
grill (scavenged)

The first step was to make a small foundation for the rocket stove. We fashioned a 18 by 18-inch by 4-inch slab with 2 x 4 lumber and a bag of premixed cement. Folks in cold places will need to make a deeper foundation to avoid frost heave.

Next we built a brick cube, leaving a small hole for the bottom of the stovepipe. For advice on how to build with brick we recommend taking a look at this. As you can see our masonry could use some more practice, but the results are not too bad–we like to think of our stove as being a bit “rustic”. You can avoid the hassle of brickwork by making a simpler rocket stove–check out these two instructional videos, one for a metal model, and another version using bricks. We chose brick largely for aesthetic reasons and we’re satisfied with the results.

Drawing from Capturing Heat

The next step is to put the pipe together fitting the elbow up into the longer pipe, and sized so that the top of the pipe is just below the bottom of the grill. Check out our earlier post for a video that can help with this part of the assembly. Serendipitously, on a bike ride, we found a grill in the middle of Sunset Boulevard that fit the opening in our brick rocket stove exactly.

You pour the ash into the completed brick cube to fill the space between the pipe and the inside wall. The ash acts as insulation to increase the efficiency of the stove. You could also use vermiculite but note that sand or soil will not work. Insulation works because of small pockets of air between particles, hence the need for ash or vermiculite, which are also non-combustible. We used a piece of scrap sheet metal with a 4-inch circular hole cut in it to keep the ash from spilling out the gap between the pipe and the squarish opening at the bottom.

Lastly you use a tin can sliced down the side and flattened out to form a shelf which you insert into the elbow at the bottom of the stove. Note the drawing above for the shape of the shelf. You put your twigs and kindling on this shelf and start the stove up with newspaper underneath the shelf. As the twigs burn you push them in over the edge to keep the fire going.

Our first test run of the stove was very successful–we boiled a pot of water and cooked some eggs in a a pan. The fire burned cleanly with little smoke except during start up. For more info on rocket stoves check out the Aprovecho Research Center.

And please people don’t burn wood inside and watch out for embers. Make sure you put the fire out completely when you are done cooking!

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87 Comments

  1. Is there a way one could adapt this to using logs? We have plenty after making a clearing in woods where we plan to have a home. Also, I would appreciate ideas to get out there before we actually have our home there (a home before a home). I don’t know if this can be done considering the size of our family: a couple in their 40s and 5 boys between the ages of 9 and 18.

    • Many people use gers (yurts) while building more permanent homes. There’s plenty of information available on building them.

    • Building it large enough to burn logs would be quite wasteful. I would recommend that you cut the logs into firewood lengths and split it to slightly larger then kindling size. You could quite possibly have several years worth of wood for a rocket stove sized for your cooking needs.

  2. Hi Bettyj,

    I’m no engineer, but I have seen other rocket stoves larger than the one I built. So I’m guessing that a rocket stove could be scaled up to handle a log, but that would kind of miss the point which is that rocket stoves are designed to make burning small pieces of kindling instead of whole logs. There is a book I have not seen yet by Ianto Evans called Rocket Mass Heaters-Superefficient Woodstoves You Can Build that has more info on rocket stoves.

    As for how to live while another house is being built, friends of mine who have done this have all relied on cheap, junky trailers. I guess it would depend on how comfortable your family is with camping. I love camping, but it makes some people cranky. Combining it with moving and a construction project could be difficult.

    Best of luck if you try it, and let us know how it goes.

    PS
    Ms. Homegrown Revolution just chimed in from the other room to suggest putting those boys to work and making them build something!

    • The Mass-heaters are a thing to behold. They are a bit labor-intensive to build, but are extremely efficient at heating…and very small amount of heat loss, and a very small carbon footprint.

      They rely on the same technology as a rocket stove…however, the design is a bit different. By using a steel tube, standing on end, with an elbow at the bottom with more tubing going to a Cob Furnace, nestled inside a steel barrel. the fumes from the cob furnace, go into the steel barrel (that has a top clearance of about 1 1/2 inches from the furnace tube), and circulate, and vented through a tube(s), that run through a bench, or whatever cob foundation you can dream up, heating it, and thereby creating radiant heat that can, and will, heat up the room it is in.

      The fuel will self-feed due to gravity., while the air flows down and around the fuel twigs, or a bypass divider. This effectively causes the flames to travel horizontally to the chimney tube.

      Rather efficient, and rather ingenious for Homesteading/Survivalism :)

  3. How much heat does that little puppy throw? Would it work as a low tech radiant heater for an outdoor party on a chilly night? How close can you sit to it when it’s hot?

    thanks!

  4. Thanks! I agree about getting the boys to help.
    I also see the purpose of the rocket stove was to not use bigger logs. Since we’ve had to make a clearing, we have both big and little ones.

  5. @ Jennifer we have been using a rocket cooker much the same as this for the past 30 years, and my wifes brother has one his grandfather built back in the 1920′s. It’s not new tech. If you want to use it as a radiant heater the simplest thing is to do what we’ve done. Make a base with a centeral pole and attach metal fans to it, better if the fans are large and split to resemble the tips of a birds wing in flight. It radiates an enormous amount of heat.

    The biggest problem with these kinds of cookers is that they need constant attention and, while they are very efficient which is a good thing, means that one poor bugger has to hang around it all the time keeping an eye on it.

    You’re better off investing in a ceramic tile heater which also uses wood fuel in small quantities but is much much better at containing and conserving the heat. A few of the more expensive, traditional models also include stoves much like an Aga.

  6. Here in Brazil we use also some copper pipes to heat the bath water, and, if you make a chamber by the stove’s side you have an oven too.

  7. Quick question here…

    I’m moving to a new apartment with a paved back yard. I’d love to build one of these, but wouldn’t be able to put a little foundation in the ground for it. It I made a concrete slab to build it on, would that suffice, or should it be grounded?

  8. Fabulous — like all rural New Englanders, I have a pile of bricks next to my barn (from a path we replaced years ago). I’ve been wanting to build an outdoor stove but never got around to it. Thanks for the blueprint and instructions.

  9. Congratulations! You built an updraft kiln used in pottery making for hundreds or thousands of years. If you really wanted to get fancy you can leave a gap in the side of the “L” shape then slide a thin brick or pottery chard in for a damper. You also might consider small inlet holes on either side going into the L channel called mouse holes that aid in air flow.
    Rob

  10. Love the idea of the Rocket Stove. I’m in the process of starting a masonry stove for the inside and when I saw this, it makes me think that it is a tiny outside version. Masonry stoves are considered also Superefficient and the bonus is they don’t need to be loaded up but once-a-day… at least what I hear. I think the masonry stove needs a new cool name… something like “Nuke Stove” or “Eco-fireplace”.

  11. Great blog and great feature on the Rocket Stove. Your comment about cobb ovens caught my eye, but the whole post was interesting because my company builds both wood fired ovens and masonry heaters or “stoves” as GreenerGuy calls them (Nuke Stove or Eco-Fireplace–he’s onto something there). Lots of low-tech DIY-ers are attracted to the cobb oven option, but you’re right, they’re innefficient and thus pretty un-green. We import an oven core–Le Panyol–from France, a much more efficient but also more expensive option. Would you care to weigh in on the two options? You can check out our ovens and heaters at mainewoodheat.com. If not, that’s ok–keep up the great work on the blog!

  12. Great article, I am converting my old brick barbeque pit to a rocket stove today!
    P.S. Your grid needs to be round like yer old iron skillet…you are losine a lot of heat at the corners!

  13. Anonymous,

    Excellent point about the round skillet/square hole. A refinement of this design should have a sort of circular sleeve that is fitted to the cooking pan/pot used on the stove. See the Aprovecho site for what that would look like. With some sheet metal, my rocket stove could be adapted to, as you point out, prevent that heat loss.

  14. Way to go Betty. My brother built a workshop with a crude apartment in the attic space to live in while he built the house. He moved in the apt in the spring and the house by THanksgiving. It was tough but he saved so much and built the house right. Good luck to you.

    Love the rocket stove. I’ll definitely try it. THanks a bunch.

  15. How about a basic rocket stove design with a 2 – 3 foot coil of copper pipe to do an instant water heater? might need a sheet metal sleeve but i think that it could be possible.

  16. I built something similar a couple of years ago. I wanted a small stove that would get hot enough to handle wok cooking. My gas range inside doesn’t put out enough heat, and buying a range built for a wok was out of the question. Basically the only difference between your stove and mine is that mine is round and has a small side hole to feed in extra air. I split hot burning hard wood stumps into small sticks for fuel and attach an air blower to the side hole. This stove gets hot really fast and stays that way as long as it is fed. I don’t know exactly how hot it gets since it burries the needle on every thermometer I have. I love my little wok stove.

  17. Great design! I use something similar for a small forge built out of a broken hair dryer, and a brake drum I pulled from a semi in a scrap yard.

    And yes, you can use logs with even this small rocket. Just splinter the logs into smaller and smaller pieces. There is an abundance of fell trees where I live, so logs are plentiful. I cut 18″ logs, and with an axe, split the logs until each piece is about an inch diameter. (once they get small enough, I use my hatchet.)

    I think I might try to turn my forge into a forge/stove/oven conversion:)

  18. BettyJ,
    I have a simple version of this rocket stove. It is dry laid brick because we are still working on the design. We have a lot of logs for our woodstove so we just split the logs to thin branch size to use in the rocket stove. A job great for teenage boys to build muscles. ;o)
    Sue, K&S Natural Farms

  19. I love the idea of rocket stoves so much that my brother and I started having them built so that they can be transportable and durable for those who are interested. These are great little stoves and we have had so much fun cooking our meals in our backyard and for camp trips. You can go to our website found at http://www.stockstorage.com if wanting to learn more and purchase one for your self.

  20. i built a rocket stove from a 5 gallon paint bucket some 4″ flue pipe and pearlite i think i spent 12 bucks
    i added a 1/4 inch copper coil in the chiminy
    an old water cooler a fishtank pump and an 8′ 3/4 in hydronic baseboard radiator ans some plastic tubing
    the coil soed not affect the cooking part of the stove at all but with the radiator inside my camper its toast warm from the same fire
    [email protected]

  21. Great Post! Building rocket stoves can be fun! We host a camp every summer (last week of July) in which folks get to come on down and learn to build rocket stoves of their own. To follow what is happening with StoveTec, a partner with Aprovecho Research Center, feel free to follow us on our blog at stovetecstove.blogspot.com

  22. I actually helped boy scouts build one of these from stones and mud many years ago for survival techniques. Mind you it was not nearly so well laid out as this!

  23. I need to adapt this stove to use a 55 gallon drum as the base ~ the cooking pot will be a galvanized tub. Would you please help me figure out the correct sizes of black stove pipe in width and lengths? I also need to build a brick one such as you have here it will use the same galvanized tub for cooking. Should insulated pipe ever be used or just the standard black stove pipe?
    Thanks for posting these videos and info!

  24. I was reading through this, and in response to stlbudd up there about the radiator heater from the same fire, I would think with some parts you can use this without a pump. Similar to how a coffee pot moves water upwards to drip through the grounds. Not positive on the exact process but I do know it uses one way valves and the boiling water pushes itself upwards. Wonder if you could get it to work for the same purpose? Being able to cook dinner, and heater water for variety of purposes would be great.

  25. Harley, it would be possible to design the coil in such a way that there is a thermosyphon created. Basically would mean the cold water from bottom of tank/heater entering the coil at the bottom, the top end of the coil then tying in to the tank/heater near the top of the liquid level.
    It may need larger bore tubing than 1/4″ to reduce resistance, which could impact on the efficiency of the system. The 1/4″ tubing being used will be giving good thermal contact and keeping the volume of the heating medium to a minimum.
    Might be a stupid idea, but maybe a thermopile could generate a useful voltage from the large temperature differential, between the rocket stove liner and the outside air, and power a small circulation pump

  26. What happens when it rains? Do you put a cover over it to keep the insulating ash from becoming wet and compacting? I’m building one and just trying to get all the details! Thanks

    • You can cover with a tarp, or my buddy built a metal cover out a metal roofin he slips over his.

      Here in the midwest we get a fair amounta rain an a course snow so we cover ours.

  27. @Brittany: Erik built the stove and he’s camping just now. I’ll ask him to comment when he comes home, so check back to see what he says. All I can say for now is that we don’t have a cover and it hasn’t bothered us so far. I hadn’t even thought of the issue before! Strikes me that it would be a problem if the chamber was so well sealed that rain water would gather in there and backwash out, along with the ash. Ours is apparently permeable enough so that has never been a problem. Wet ash doesn’t seem to be a problem.

  28. This is EXACTLY what I hope to do! I am so thankful you posted this materials listing and instructions! Would you change anything- Now that you have used it? If not, I plan to copy it to spec. The only thing I think I might like to change is that I might like to “expand” it…doing this 4 times – so I have many “burners” to work with for large group cooking and canning. It will be our primary stove for about 4-5 months out of the year. I know people say “don’t put them inside”…but I am thinking I would like to put it at the end of an open porch with cement floor, since it will be our summer kitchen for so many months ir would be nice to have cover (form hot sun and rain) and also have an option to possible screen in if needed. From your experiance with it thus far, do you think that would be a big deal to do that? I use my super high powered propane turkey burners (6 of them while doing large canning projects!) that way and they give the same warning. I would love to retire my propaone units for wood once and for all!!! I would love to hear your thoughts. Thanks a bunch.

  29. Thank you for posting this! I have an outdoor camp fire area that I presently use for cooking but like the idea of this one for just using little branches, twigs, pine cones and corncobs. I will be looking into doing one of these this summer.

  30. Well I just have to say that this is fantastic. My family often cooks outdoors…so my mother and I are gonna build this out in the front yard. I’m very excited to start this so if anybody has any tips…I will be visiting this cite again. Oh and I live in Washington state so weather can get pretty bad! Any advise what I should do for maintenance?

    • ejefferson, thanks! Did you find this via our new post or from google? Because we just put up a post with instructions for another kind of rocket stove, which you might be interested in if you haven’t seen it:

      http://www.rootsimple.com/2012/03/rocket-stove-made-from-five-gallon.html

      As to your weather question, the biggest weakness in the brick model is the open top–the ash insulation is exposed to water. We don’t live in a rainy climate so we can get away with this, but it is sloppy design. If you were to build your own you might want to think of ways to make a sort of cover for the top. But the brick and vent pipe are fine in the rain.

      The portable stove in the new post would rust eventually if left out in the rain, but it’s portable, so you could tuck it away when you weren’t using it.

  31. This stove looks amazing and seems easy to build.

    Has anyone built a backyard version of the Rocket Bread Oven? I’m trying to figure out how to make a smaller version that wouldn’t require a 55 gallon drum.

  32. any insight on the state of the tin can inside? has it corroded or deteriorated? i´m working with some that have been warping and coming apart, looking for new chimney material suggestions. thanks.

  33. SA WEET! So making one of these! I have 3/4 of what I need. Will be surfing the roadsides for the rest of the free materials needed for this!! I have several old oak trees that will most likely provide me with the fallen fuel to cook for FREE! Propane sucks! Namely sucks the dollars from my wallet!

  34. During our recent transition to WordPress, we lost a few comments. This is one:

    On 11/7/12, Brett Bowden wrote:

    I built a similar thing in S. Africa, and put in a 30 ft length of 1/2 inch flexible copper gas piping, coiled around a pipe for the shape, down the chimney to heat water. The longer the pipe the hotter/quicker it is. You could do away with the chimney also as the piping acts like a chimney if you coil the pipe around a 6 inch plastic pipe and then take the plastic pipe out, leaving just the coiled copper pipe. As long as your water supply side is higher than you outlet side it will feed automatically. I put a valve on it to control the flow rate/switch it off when needed. Beware when it’s hot though it spits and jumps like crazy! Best to let steam cool it down and increase the flow slowly until you have the right temp.

  35. Question: If rain gets down into your stove and wets the ash, doesn’t that ruin the ash and make lye pour out the bottom of the stove?

    • Short answer is it didn’t matter to us. We don’t get a lot of rain here, first, and as someone who has tried to make lye from wood ash I know how hard it is to get a strong solution, so I never had any concerns about us coming to harm from contact with seepage (esp. as our ash was park bbq ash, not hardwood ash) If there was any lye-ish overflow it soaked back into the brick. Any water that got in there didn’t seem to harm the insulating properties. Of course the easy solution to any worries along these lines is to keep the top covered when it rains. Our other rocket stove (see the link at the top) is totally self enclosed.

    • Robert–thanks for catching that error. It’s galvanized steel, so no melting problems. I’ve fixed the post.

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  37. This is such an efficient simple design. I think I’ll try and experiment one with an inline copper tubing before adding vermiculite for heating some water. If anyone has some sketches or tutorials that I could learn from I would appreciate if you could post that here!

    In the meantime I’m trying to wrap my head around using this system to grill some chicken but seems far too dangerous if grease drips down into the pipe and catching on fire. Not quite sure if a grease-tray would then grill the chicken…and make it less dangerous (?) Any ideas to overcome this?

    Cheers!

  38. I am definitely building one of these! So easy and inexpensive and so important to have. Even with a wood burning stove in my garage shop this will come in handy as a spare. . . Thanks for all the useful information

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  44. I plan to build one of these soon, but I am curious, do you think this gets hot enough for canning purposes?

    • I think it might take a larger rocket stove, but it would work. It would also be someone labor intensive–you have to keep feeding a rocket stove.

    • A larger rocket stove would probably be better for canning than the one I built. But I think it could work. It would be labor intensive to keep it fed with twigs.

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