I love rocket stoves... For those that don't know it's a great way to cook with wood. The basic principle is to burn wood hot and fast, which is more efficient. So you insulate the fire and direct the heat to where it's needed... The pan!
- 2x 20 litre oil cans (easily found outside you're local kebab shop)
- A cooking pot
- Lots of wood ash
- A length of 4" flexible flue (not aluminum dryer stuff)
- Some sheet metal
- A couple of lengths of metal tubes (optional)
- Tin snips
- Work gloves
- Rivet gun
- Angle grinder (not essential but speeds things up)
Work gloves are important, this involves lots of sniping of sheet metal and it can be a painful if you don't wear gloves!
Step 1: Materials in more detail
I guess you could make a rocket stove out of anything, but these 20 litre oil cans are perfect and very common in the UK, very easy to find in the street.
Again, you could make the burn chamber and stack out of anything, and in fact a 90° corner to the burn chamber is better... But this 4" flexible flue is easy to work with and I had some lying around, so that's what I used
This isn't aluminum dryer flue, which I'm guessing would burn out fast, but stainless flexible flue designed for a chimney stack. You could use anything, I've seen people get clever with normal sized tin cans.
The pot for the rocket stove needs to fit pretty snug, a 1cm gap around the edge is best. The pot shouldn't have any plastic handles or anything as they will melt. Also a good fitting lid is important, as we all know that things boil quicker with a lid! I prefer a pot with two small handles on either side, rather than one long handle, as it's makes a smaller footprint when in storage.
I used sawdust as the insulator, you could use anything that's a good insulator that's fire proof. I've heard of people using vermiculite. I like sawdust because it's free and I quite like the fact it's heavy, makes the whole stove way more stable when in use. But it's pretty heavy to move around!
Step 2: First cuts
Chop the top off one of your oil cans. You might need to use a punch and hammer to make a hole and then use the tin snips to cut around the edge.
All the way through this you should be aware of sharp metal, at every stage I used a good pair of pliers to crunch up sharp edges and files to shave off anything sharp.
Chop both the bottom and top off the second oil can.
Step 3: Starting on the burn chamber and stack
Cut the flexible flue square, a mixture of hacksaw and tin snips works well.
Then cut little tabs into the end and use a pair of pliers to fold them back and squash them flat (photo 1).
You're aiming for a nice flat edge that isn't going to cut you to shreds when you're stoking the fire (photo 2).
You now need to cut a hole in the oil can which still has a bottom for the flue. An inch of so from the bottom is good (photo 3).
Push the flue through the hole and bend so that it's a sharp an angle as you can manage and the flue is roughly in the middle of the can (photo 4).
Step 4: Make a lid
You could re-use the tops and bottoms you cut out the oil cans for a lid, but I had some sheet metal lying around so I used that instead.
You want to cut a piece of metal that fits in the oil cans and has a big hole for the chimney stack. I got the angle grinder out for this but I'm sure there's plenty of different methods to achieve the same thing.
Try and get the fit as tight as you can, but don't worry too much, wood ash is amazingly stable once it's settled down.
Step 5: Insulation station
Time to fill the rocket stove with the insulation material.
My friends collected me a bunch of wood ash, which is an amazing insulator as long as it's dry.
You want to fill the stove as much as you can, watching out for nails or anything that is a conductor rather than an insulator! Pat it down, pick out any big chunks of charcoal.
Don't worry too much if ash comes out around the flue that sticks out of the can, with a few uses it'll be so compact that you won't loose any more ash.
Once you've filled the can squish the lid down as best you can.
Step 6: Make a pot stand
Some people who make rocket stoves just rest the pot on the flue and make some cuts in it for air to get through.
I'm a BIG FAN of using the top of a gas bottle as a pot rest. I just cut it down so there was 20mm between the top of the flue and the bottom of the pan. And then I cut a bunch of slits so that air and FIRE could flow nice and even around the pan.
Way more stable and hardcore than trying to use the flue. Plus it's a great use of the tops of gas bottles once you've made wood burners out of the rest of them.
Step 7: Sort out your skirt
So now we've got an insulated hot burning fire that's going to hit the bottom of your pan with plenty of air and space for a good fire.
So we need a skirt. This forces the heat up the side of pan for the best heat transfer into your food and also creates a great draw for the fire.
Measure up against you pan and then cut the second oil can so it'll fit over the first and just give you enough space to grab the pan handles.
Slide the second can over the first. This might take some hitting with hammers. As it's probably going to be a tight fit.
Step 8: Optional: Handles
Rocket stoves weigh quite a lot (if using wood ash) and can be buggers to move around, so a couple of handles are a good addition.
Some people like to leave the skirt flexible, move it up and down so it'll work with a frying pan or a deep pot or whatever. I just choose a pot and that's the one for the stove. Which allows me to fix the skirt in place, and bolt handles in place.
I've always got bits of bike lying around so I just bent a couple of tubes into handle shapes, drilled them and then bolted them into the stove. I used the overlap of both oil cans to bolt through, holding the whole thing together. I also riveted the cans together, nice and strong.
Step 9: Final detail: Wood shelf
The first stove I built I didn't think this was that important so left it out. Wrong. This is totally needed.
Cut a piece of metal sheet that cuts your flue in half and sticks out a little bit.
You feed the wood in the top half and the air draws in the bottom half, hits your fire and burns like hell.
Very basic, but very important.
Step 10: Finished: Test Fire
First off, aim the side flue into any prevailing wind... Air makes good fire.
You stoke the fire from the top. A little paper and some very fine cut wood to get it going.
Light it, let it burn for a minute or so.
Then start feeding in wood from the side, using the shelf. Wood in the top, air in the bottom.
Get the pan on quick, the pan restricts the air flow, makes for better draw.
This thing burns fast and quick, you want to feeding small cuts of wood into the fire, keep pushing it in with sticks as it'll will burn quick.
Bark has a natural anti-fire thing in it, so if you can avoid twigs with bark, cut fine dry pine works great.
On our first burn we boiled water in three minutes with very little wood. A success.
From the last photo you can see how hot this burns.
No smoke, no ash, that's a good fire.
P.S. Might be obvious, but wood ash is only a good insulator when dry... Don't leave your rocket stove out in the rain!