Rocket stoves use twigs to cook food quickly, efficiently

When I visited Kelly Coyne and Erik Knutzen of Homegrown Evolution last week they showed me the rocket stove they made in their backyard. Theirs is quite fancy because it is made of bricks. They sometimes use their rocket stove to fry a meal in a skillet.

The rocket stove was invented about 10 years ago by Dr. Larry Winiarski at the Aprovecho Research Center in Oregon. It consists of an elbow-shaped combustion chamber (usually made from metal cans) surrounded by insulating material (often a large can filled with sand). It uses twigs for fuel, so it's ideal for areas where the trees have been depleted.

Here's a video from the Aprovecho Research Center that shows how to make a rocket stove.

Here are the first 3 of 10 rocket stove principles, by Larry Winiarski.

1.) Insulate, particularly the combustion chamber, with low mass, heatresistant materials in order to keep the fire as hot as possible and not toheat the higher mass of the stove body.

2.) Within the stove body, above the combustion chamber, use an insulated,upright chimney of a height that is about two or three times the diameterbefore extracting heat to any surface (griddle, pots, etc.).

3.) Heat only the fuel that is burning (and not too much). Burn the tips ofsticks as they enter the combustion chamber, for example. The object is NOTto produce more gasses or charcoal than can be cleanly burned at the powerlevel desired.

Illustration from In the Wake, a cool website on various simple off-the-grid tools.

• [ployntabs]

  Where am I gonna find something to fire my thermal bricks at 1000 degrees? My stove doesn’t go to eleven.

• [johnpaul]

  I made one of these in Africa a while back. I was working in the DRC for Doctors Without Borders, and in my spare time me and a buddy of mine (Swedi) started to experiment to make refractory ceramics (insulating clay tiles essentially) out of sawdust and local clay. The best clay in that part of the Congo (south kivu) came from underneath old termite mounds.

  We built the stove and it worked well, consumed less wood etcetera. But we could never get Swedi’s wife to care. I talked to her about it, after all, she was the one who brought cooking wood in from the forest, but for her learning how to use a new technology was more of a challenge than bringing in more wood and doing it the old way. I know that with more effort on our part we could have introduced the stoves more widely and maybe caused some forest conservation/eased the burden of the local female population. But I couldn’t because we had a medical program to take care of.

  Anyway, what Aprovecho did so well is design something that is not DIY, but is build-able in rural settings from local materials and very usable. It is in fact a wood-gasification stove, in that it burns not just the wood but also the off gasses and smoke. This is how it achieves the 20x efficiency boost over an open fire. They actually developed the idea when working at a Guatamalan Refugee camp (sorry if my facts are off, I’m writing from memory and not wiki) and managed to figure something out that they could jerry rig out of available materials (that time it was metal cylinders and not ceramics but it worked in the same way). Refugee camps exact a brutal tool on surrounding ecosystems and people quickly run out of resources like cooking wood. This little do hickey made all the difference in the world, and I hope innovation like this continues to flourish and spread.

• [bluzshark]

  Anyone who heats with wood stove would know that this is simply a chimney fire. Creosote builds up in the elbow of the stove pipe, ignites and sends up a rocket of flame through the brick or stone chimney. http://www.naturalhandyman.com/iip/infchimneyfire/infchimneyfire.html

  For a great back yard fire, Try doing what we do in New Hampshire.
  1 Square off the ends of a hollow log, about 5 ft tall , 18″ diameter or better. Set it on 3-4 cinderblocks so it is elevated above the ground. use 3 or so metal fence posts to prop it up sturdy.

  2. Light a small fire underneath the hollow log.

  The Hollow log will act as a chimney directing the smoke out the top. Soon the interior of the “chimney” will ignite and the draft from being elevated will produce a vaccum with air rushing up. That super heats the gasses and what you get is a roman candle effect, like a tall candle burning out the top. Here’s an example, but none of a Yankee version. You gotta have it at least 5 foot tall for real fun http://edcommunity.apple.com/gallery/student/item.php?itemID=1430

• [Dillenger69]

  Firebrick is easy enough to buy at the hardware store.

  I wonder how well this design works with a few charcoal briquettes as the fuel source. I don’t exactly have lots of sticks lying around my back yard.

• [Takuan]

  to spread this kind of tech in established cultures you have to let them think they are stealing it from you. Set up a stove, use it, then sell firewood. Let your customers know its because you have the stove you have the surplus. Feign anger if they want to look at it. In a month everyone will have one.

• [Takuan]

  2000 degrees F. With HDTV as the standard, there should be plenty of lenses in the trash heap
  http://www.instructables.com/id/Giant-Fresnel-Lens-Deathray-An-Experiment-in-Opti/

• [Antinous]

  Apparently you really have raised children.

• [Takuan]

  they always had access to natural graze and outside air. Regular FDA inspections too.

• [eustace]

  Then they had it better than Emo Philips:

  When I was a child, my parents told me
  “Don’t go near the cellar door
  you can play anywhere else you like
  but don’t go near the cellar door”

  One day, when they were gone
  I went to the cellar door
  and I opened it

  and I saw things

  things I’d never seen before

  trees, and grass, and the sky…

• [gator]

  I used a kelly kettle on our last scouting trip. It is kind of hard finding them in the states. I did a google search and found a stainless steel one online at http://www.preparednesshelp.com/kelly-kettle/cat_22.html

• [presterjohn]

  but what about the carbon emissions? ok, sorry sorry.

  At MakerFaire, there was the guy running a diesel engine off gassification of woodchips, and piping his carbon exhaust into an algae tank (realistically it would have taken a huge number of algae tanks to deal with the carbon exhaust, but it was proof of concept.)

  There is so much to be gained in efficiency in energy generation and usage.

  BoingBoing should do something on the Sterling Allan’s FreeEnergyNews.com / PESWiki.

• [Takuan]

  why do ya think I suggested fresnel solar?

• [Geoff Sebesta]

  We use these at the Rainbow Gathering. It makes coffee with little effort.

• [Takuan]

  I can’t remember the proprietary name for it, but there is this white fireproofing material they use in foundries and furnaces that is AMAZING. It’s light, friable and easily attached with pop rivets and washers. Kind of expensive, but really works well. I’m still waiitng for cheap aerogel.

• [mdhatter]

  I’m totally making one of these.

• [Takuan]

  kinda like
  http://www.oldjimbo.com/survival/kellystove.html

• [jeffbell]

  There is a turbo variant which uses a fan to push the air though, called the sierra stove.

  http://www.kk.org/cooltools/archives/000012.php

• [Mark Frauenfelder]

  Ooh – that Kelly Kettle is cool!

• [Anonymous]

  I wonder how this compares to the DIY wood gasification stoves out there? (As in: http://journeytoforever.org/biofuel_library/WoodgasStove.pdf)

• [Takuan]

  ‘spensive though
  http://www.oldjimbo.com/survival/kellystove.html

• [rosichan]

  The Kelly Kettle and the Rocket Stove are not the same – except that they both burn twigs. Something similar to the Kelly Kettle, but with the water in the inside chamber and the fire in the outside, would probably heat faster and with less fuel.

  One of the advantages of the rocket stove, that I didn’t see mentioned, is that it produces less smoke. Indoor cooking smoke is a leading cause of blindness in situations where an open fire is used.

• [Takuan]

  whoops, that link was supposed to be the Lee Valley catalog showing a price of ninety-five bucks.

• [jonpartain]

  I’m not sure if it’s a coincidence or not but the physics is very similar to an Anagama Kiln, which is an ancient (5th century) wood fired ceramics kiln from Japan via China via Korea…
  http://en.wikipedia.org/wiki/Anagama_kiln

• [Maybe]

  Interesting article, Mark, and timely for me! I’ve been learning a lot about alternative cooking this week at http://solarcooking.wikia.com/ — I think solar cooking might be worth an article of its own, as it can do a lot to preserve forests in places such as refugee camps where firewood is scarce and women who need to gather it place themselves at risk. Solar cookers can be made with nothing but cardboard and tin foil, or even reflective car window shades! Please take some time to look around the wiki, and maybe talk to the founder Tom.

• [KWillets]

  For the DIYer’s, there are videos on youtube of how to make a highly efficient wood gasification stove out of food cans — it appears there are a number of backpackers working on efficient wood/biomass stoves, like this one: http://www.garlington.biz/Ray/WoodGasStove/.

• [Stefan Jones]

  Hmmm.

  Could a coal burning variant of this be designed?

  The Chinese use cake-shaped lumps of processed coal in their home stoves. Imagine if they got coal sticks instead, designed to be shoved into a variant of these. Hotter, cleaner.

• [Robert]

  Maybe you can fire the bricks in a clamp kiln? Apparently it only requires a pit dug in the ground, sticks, and fire. Light the fire, put the bricks in, surround with sticks, cover with earth leaving a hole at the top, and wait overnight:

  http://www.butser.org.uk/iafimg5_hcc.html

• [Avi Solomon]

  Ianto Evans, the Cob House builder, has a great book on building rocket stoves:
  http://www.rocketstoves.com

• [Takuan]

  looks like charcoal burning

• [Abelard Lindsay]

  For my money (and it does require lots of it to install), nothing beats a masonry heater. Mark Twain agrees:

  http://www.timelyconstruction.com/MasonryHeaters/MarkTwain.htm

• [Taniwha]

  Also like a thermette something my dad brought back from WW2 and used while camping to make tea/coffee

• [triskelion]

  It looks like a Kelly Kettle to me: old hat. My dad bought one years ago.

• [Anonymous]

  OP: Invented ten years ago? No, maybe you mean put on the market ten years ago. See #8, too.

  My grandfather made these things all the time out of milk cans and some other tubular steel thingee he always had laying around. Also, taught me the secret boosting the range on the potato bazooka. Nope, not sharing. :)

  @10: Stefan, yup, my grandfather stored coal in the lower half of the milk can when he’d take it along to tailgate. Toward the end he was getting bonkers with his “recycling” and would mix with sand for the lining for the “quicky” make-dos. So, I’m unsure how well that worked. He was trying all sorts of fancy insulators. And rocket fuels.

  Cuz it was then I understood why they call’em rocket stoves. Grampa would sometimes mix up some paste, let it dry some, and shoot off the stove. He was always “working on the mixture” which was a euphemism for all sorts of things in grampa & gramma’s house.

  Good times!

• [themindfantastic]

  There was an instruction set to make a cheap variation of a rocket stove in the book, Recipes for Disaster by CrimethInc. Its made out of Two 15 Ounce Cans (common size vegetable can) One 26 Ounce Can (less common, beans often come in cans this size) Two One gallon cans (Found in Dumpsters of restaurants especially pizza restaurants), Annealed Tie Wire (hardware stores used for tying rebar together in steel reinforced concrete) and Insulation (Cob {mixture of clay, sand, and straw} is one, but ashes work better, though perlite or vermiculite to fill out the ashes can be used, and found easily in garden stores). I should make one with these instructions and make an instructable out of it honestly.

• [caseyd]

  I wonder if the sierra stove’s fan could be powered by one of those squeezy / shakey flashlights.

• [KWillets]

  It’s really unrelated to the Kelly kettle or things which try to maximize heat transfer by burning within a water jacket. Burning next to a relatively cool surface tends to cool the fire gases before everything is fully burned. Higher-efficiency boilers use a separate combustion area before the heat transfer.

  This is designed to be a high-temp combustor which is simple to operate. I don’t think it’s close to the efficiency of an EPA-rated woodstove, but it’s cheap and parts are easy to get in, say, Darfur.

  It doesn’t look like there’s much in it that hasn’t been done before. For instance a Korean Ondol has a similar combustion chamber, with the same fuel-feed via a port at floor level. I once saw a picture of a woman feeding stalks into one of those with her feet, which would alleviate one PITA with this: continually feeding fuel.

• [LYNDON]

  @ #12 Yay the thermette! A classic piece of kiwi camping equiptment and, my mother assures me, great for kids – send them scampering off for kindling to work off some energy before dinner.

  A portable one of these things could be deployed in the same way.

• [Bennessy]

  Now I can finally put my fagots to use.

  http://www.merriam-webster.com/dictionary/fagot

• [BrerMatt]

  There’s also the Justa Stove which takes the rocket stove and combines it with a plancha style grill by running the heat under the stove surface:

  http://www.crest.org/discussiongroups/resources/stoves/TWP/justa/Justa_stoveone-pager.pdf

• [Takuan]

  masonry heaters are/were common throughout Northen Europe/Scandinavia. Not very portable though.

• [Takuan]

  @30 That also means “meatballs” as well as your somewhat clumsy wordplay. Please pay attention to your larger connotations else you cause unwitting offense and get stomped.

• [Takuan]

  That Justa reminds me of kilns. I wonder if kiln design in pottery cultures leads cooking stoves?

• [arkizzle]

  Yeh, I won’t have anyone bad mouthing meatbealls around here.

• [Takuan]

  for the cottage in summer maybe; a solar cooker using the kelly/thermette principle and the fresnel lens from an old back projection TV. There’s a good instructable about a rear-projection lens solar death ray with details. I scooped one from the e-wasters a month ago and intend to try it. The focal point without a colaminator ain’t tiny, but I think you could boil a gallon in less than an hour with the right set up. Free, no emissions, sun dependent.

• [Antinous]

  Nonsense, Tak-kun, BB comments are a fine place to come out of the closet.