A Rocket Stove Made From a Five Gallon Metal Bucket

The principle behind a rocket stove is simple–rather than cooking on an open fire, you burn wood in an insulated chimney. Rocket stoves are highly efficient and easy to make. They run on twigs, so you can avoid cutting down a whole tree just to cook dinner.

We’ve had a rocket stove made out of brick in our backyard for several years. The post we wrote on it in 2007 is–oddly–the most frequently searched post on this site. I figured that since there was so much interest in the topic it would be good to offer one that didn’t require masonry work. Better yet, I figured that it should be portable, so I made it out of a five gallon steel paint bucket. (eta: for your googling pleasure, it seems retailers call these cans “steel pails” rather than buckets). The project took less than an hour to complete and I’m very pleased with the final result. We created a pdf with full instructions that you can download at the Internet Archive. What follows are some photos showing the building process:

Using a piece of 4″ vent pipe and a 90º elbow, I made the chimney. See the pdf for the exact dimensions.

I traced the outline of the vent pipe on to the lid of the bucket and cut this hole out with a jig saw. Tin snips would also have worked.

Using the vent pipe as a guide again, I cut out a 4″ hole near the bottom of the bucket.

I used one part clay (harvested from the yard) to six parts vermiculite as my insulation material. Mixed with water, the clay holds the vermiculite together. I could also have used dry wood ash, but I had the vermiculite and clay on hand so that’s what I went with.

With the vent pipe in place, I packed the insulation into the bucket and let it dry for a few days before putting the lid on.

I found a barbecue grill at Home Depot that rests on the top of the bucket to support a pot.

Next you want to get yourself a tin can, take off both ends and open it up with tin snips. Cut a piece to serve as a shelf in the mouth of the pipe. It should be about 4″ long–so it sits forward in the mouth of the vent. The rear part of the vent, where the fire burns, is open. The twigs rest on top of the shelf, the lower half is for drawing air.

The last step was to add the new Root Simple stencil to the back.

Some fire tips from the little lady, our resident pyro:

A rocket stove isn’t like a campfire–you don’t throw on a big log and kick back. Cooking on it is intense and concentrated, best suited for boiling or frying. The best fuel source is twigs, small ones–I prefer pencil-sized twigs, and I never try to burn anything thicker than a finger.

To start a fire just shove some paper or other tinder under the shelf toward the back of vent. Lay some very thin twigs, pine needles or other combustibles on the shelf. Light the paper and watch it go. Start adding larger twigs to establish the fire. Of course, twigs burn fast and hot, so you have to keep adding more fuel. Also, the twig are burning from the back (the fire is concentrated in the bend) so as the fire consumes the sticks, you just keep shoving the unburned parts to the rear.

There’s a balance between choking the vent with too much wood and having too sparse a fire. After a few minutes of playing with it you’ll get the hang of things. If you’re doing it right, there should be no smoke, or almost none. These things burn clean.

Let us know if you like the pdf and if you would like to see more similar instruction sheets (maybe in an ebook format) of these types of projects. There’s also a good book on using rocket stoves as heaters:  Rocket Mass Heaters: Superefficient Woodstoves YOU Can Build by Ianto Evans and Leslie Jackson.

A Redneck Rocket Stove

From Wes Duncan, the “High Tech Redneck,” a rocket stove made out of cinder blocks. I’ve built one of these too and can confirm that they work great. And you can’t beat the price. Time for some redneck cookin’!

Update: As several readers have pointed out, this design ain’t safe. Cinder blocks can explode and were not meant to be placed next to a heat source–that’s what fire bricks are for. See our post about our backyard rocket stove for a safe design that uses metal pipe.

StoveTec’s Hot Rocket Stoves

StoveTec’s wood burning rocket stove on the left, charcoal and wood on the right.

A reader comment alerted me to a very cool product, the StoveTec Rocket Stove, offered by the “not-just-for-profit” wing of the Aprovecho Research Center. Profits from sales of the stoves benefit the Center’s research. StoveTec sells two rocket stoves, one for wood and the other for both wood and charcoal. While I haven’t tested one, the $37 to $40 price is a bargain.

Rocket stoves are a simple “appropriate” technology that burns small pieces of wood and charcoal efficiently. We’ve blogged about them before and even constructed our own out of a vent pipe and bricks. Instead of burning a log to cook you can use trimmings from trees, bushes and even agricultural waste. According to StoveTec,

“StoveTec Stoves, rocket stoves invented by Dr. Larry Winiarski, use 40-50% less fuel and reduce emissions by 40-75% while reducing green house gas (GHG) emissions an estimated 60% or 1-2 tons per year. These stoves are preferred over other improved cook stove and three stone fires by 95% of users in Uganda. High adoption and preference reported in India, South Africa, Ethiopia and Chile proves the stoves great versatility among many different users.”

Looks like they could find a nice home in North American as well. Do some pruning and then cook dinner. How about a rocket stove tailgate party?

Appropriate Technology

Our rocket stove, pictured above, was mentioned on BoingBoing last week and we thought we’d use the occasion for a brief roundup of similar “appropriate” technology concepts. The term appropriate technology evolved out of political economist E. F. Schumacher’s book Small is Beautiful and is easier to show rather than describe. While not always low-tech, appropriate tech concepts feature elegantly simple (but not simplistic) design, efficient use of energy and are usually aimed at poor countries. What Homegrown Evolution would like to prove is that these technologies have a place in developed western countries as well. Here’s three of our favorite appropriate tech ideas and websites:

1. Rocket Stoves: our brick rocket stove and a link to a video on how to make a simple metal version.

2. The glorious Solar Cooking Archive which has links to dozens of simple solar cooker plans that you can build yourself. We built our cardboard and aluminum foil Pavarti cooker with plans from the solar cooking archive.

3. AfriGadget. The subtitle of this blog says it all, “solving everyday problems with African ingenuity.”

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!