We’ve been led to believe that redundancy is inefficient but redundancy built into a system creates a resilient system. If one function falters another is there to provide backup. Many of us have a few days – hopefully weeks – worth of food stored for emergency purposes but other than the odd candle and a few spare batteries for the flashlight, most do not have a means of preparing a meal in the event of a power failure. A rocket stove solves this dilemma.
These little stoves provide an amazingly efficient way to extract heat from limited fuel resources. It’s possible to cook for a 2-hour period using a three-foot long 2 X 4 pulled off a pallet. This post will explain how you, too, can build a rocket stove. And besides emergency uses, they’re great for outdoor cooking or camping.
What you’ll need:
- Two 398mL food cans – the most common type for beans, veggies, etc.
- One 675mL food can – these are slightly wider than the standard can and substantially taller. Most often found with tomato products in them – whole, crushed or sauce.
- Two 2.84L food cans – these can be found at most restaurants, especially pizza joints. They often have pizza sauce, jalapeños or pineapple in them.
- Rebar tie wire – available at any home hardware store (usually about $5 a roll).
- Insulation – cob and either wood ash, perlite or vermiculite (a 9L bag sells for about $8 at any garden store).
- Can opener
- Tin snips
- Permanent marker
- Work gloves (highly recommended, as tin is extremely sharp)
- Remove the labels, glue and food residue from the cans.
- Cut off the top and bottom of the two small food cans; cut off the top of the 675mL (mid-sized) can; cut off the top of one large can; and cut off the top and bottom of the other. Save one of the lids of the large cans for later.
- Trace the bottom of the mid-sized can on the side of the large can (the one with its bottom in tact), approximately 1 inch from the bottom. Use your tin snips to cut out the circle traced on the large can. Go easy because you want the joints to be fairly tight.
- Trace the bottom of a small can on the side of the mid-sized can, starting right at the bottom. Cut this circle out with your tin snips. This is where the chimney will go up.
- Make a 2-inch cut lengthwise on one of the small cans, thus allowing the 2 small cans to fit snugly in the end of each other. Now you have a tube slightly shorter than 2 cans tall. This is the chimney.
- Slide the mid-sized can into the large can, facing the cut in the mid-sized can upward. Slip the chimney into the mid-sized can, pushing it in just enough to cover the hole.
- Pour the insulation around the bottom of the mid-sized can, with just enough to support the mid-sized can, which comes in horizontally. The chimney should be centred in the large can.
- A bit of cob can be used to seal up the joints, though this is not entirely necessary. Cob is also useful to keep the loose ash, perlite or vermiculite in place – cob is simply a mixture of sandy clay soil (~80% sand; 20% clay) with some straw (optional in this case).
- The remaining space – around the cob if cob was used or simply around the tin innards – is topped off with insulation.
- Cut the lid of a large can to make the firebox shelf. The shelf should be slightly lower than the mid-point of the firebox. It can protrude but be sure that it is not shoved so far back as to divide the chimney. This will most certainly starve it of needed air. Fuel will sit on top of the shelf, while the ash will fall below.
- The final step is building the pot rack. This is where the second large can comes in. Slice the can lengthwise, so it will slide over the second large can. Now using the lid of a small can, trace a series of holes along the top of the second large can, leaving enough room so the can remains strong (remember: this will carry the weight of a pot and its contents). You’ll want to leave about 1 or 2 inches between the top of the chimney (the burner) and the top of the pot rack.
- Using the rebar tie, fasten the pot rack onto the stove assembly. Use at least 3 ties to secure it, tightening the wire with pliers until sturdy.
- Your stove is ready to use. Wood should be short and about the width of your finger (branches work great), using small pieces of paper to get it going. Start it at the front of the firebox, pushing it back once it gets going. As soon as the chimney heats up, you’ll hear why a rocket stove is called a rocket stove. It really sucks! Note: don’t overload the firebox – keep half the area open for airflow.
So that’s a rocket stove. I just built it last night but this morning I boiled water for tea in just a few minutes. Tomorrow I’ll cook my morning oatmeal on it! It might not be my main cooking appliance but given the countless piles of branches that I see in the alley destined for the landfill, I may end up using it more and more. It’s a darn good productive use of branches too large for the compost, yet too small for the cob oven.
How We Can Help You:
Dirt Craft offers several Rocket Mass Heater workshops (upcoming dates here) each year, so you can get hands on experience designing and building a system. We also provide advice if you’re thinking about building a rocket mass heater. Or (this is something we do quite often), if you’re trying to trouble-shoot something that’s not quite right with one you’ve already built. Visit our Consulting page for rates, and contact us to get started.