Rocket Stove

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!

Materials needed:

• 2x 20 litre oil cans (easily found outside you're local kebab shop)
• A cooking pot
• Lots of wood ash
• A length of 4" stainless-steel flexible flue (not aluminum dryer stuff) (or get creative with tin cans? Any steel pipe?)
• Some sheet metal
• A couple of lengths of metal tubes (optional)

Tools needed:

• Tin snips
• Work gloves
• Drill
• Rivet gun
• Angle grinder (not essential but speeds things up)
• Hacksaw

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!

Comments

[perfo]

nice job. A question on operation if you don't mind.

when you initially put the fire down the flue and get the air moving in the right direction did you need to blank off the top shelf part ? I'm curious why the air won't be sucked in via the top shelf as well ? I can see the air flow will still be correct but the burn area may move back up the fuel ?

[andytompkins]

You don't need to block off the shelf or anything. This things burns so fast you keep pushing the fuel in almost constantly, so the fire doesn't get a chance to spread back up the fuel.

[perfo]

Thanks...
I didn't doubt it works of course but I'm still not quite sure of why :)

[rbodell]

heat raising up causes the draught that fans the fire. Ever blow on a campfire?

[neaton1]

As nice as seeing the potential reuse of dryer vent tubing, how well has it held up to the temperatures of the cooking fires?

[andytompkins]

It's not dryer vent, see comments below and I've just updated the 'ible to say that I used stainless flexible chimney flue... But you could use anything!

[rbodell]

I would stick with stainless. My rocket stove will melt aluninum.

[neaton1]

My bad... I mistook it as such by mental association..

[SabastianW]

Hey. Sab here, hows things andy long time no see, i have recently obtained an allotment of a rather large size and im doing projects up there at weekends, im currently building a cob hut with rocket stove mass heater, thermal dynamic water heater system, solar powered charge points and a water filtration system, along with a couple of other little missions, hopefully youve still got my number ? Contact me on facebook if not ;) keep up the good work

[hyperfocused72]

Nice to see you using a skirt. Without one you lose so much efficiency you may as well make a campfire. Amazing how many people building rocket stoves don't know this.

[joen]

Someone asked about the ash and where it goes. There is very little ash build up because the stove burns very completely. Also because of the natural updraft a lot of the ash that does not get burned goes up the flue. You would be surprised at how long you can keep it burning and how little ash will be left. And because of the insulation, the hot coals that are left will burn down to almost nothing. In my experience at least, ash build up is a non issue.

[andytompkins]

Exactly! Well put...

[kobejn]

no to je paracek .]

[mateo90metal]

Se ve interesante!

[totally_screwed]

A great instructable.

Aluminium as pointed-out will not work (it will sooner or later oxidise and or melt).

Please be careful about using galvanised (zinc-coated) steel sheet. Zinc-coating prevents the iron from rusting. However for hot applications and or welding the zinc presents a health hazard. A lot of steel is galvanised and the zinc will burn-off, producing nasty toxic fumes. Be careful.

Vermiculite is an excellent insulator, but see references.

For dimensional and design guidance on rocket-stoves, see:

http://www.aprovecho.org/lab/rad/rl/reg-rep/doc/81...

http://www.aprovecho.org/lab/rad/rl/stove-design/d...

[Ricardo Furioso]

Stainless steel flue is brilliant >>> but expensive.

I'm not understanding where the ash from your burn goes. I'm thinking the ash would be minimal, but what if you were baking or making stew or something that took awhile to cook?

Those oil cans are harder to find in California. Most everything here seems to come in plastic 5-gallon buckets.

Thanks for the excellent instructable.

[spark master]

Anyplace that uses deep fryers may have square cans. I know several Chinese places that go through at least 1-2 5 gallon cans a week. I made one fer scouts and we never used it, although I fired it up at home, and it blazes pretty good.

I had 2 cans, the first one I cut a hole for flue pipe (I believe it was 4 inch), then I cut the top out (leaving the rim using a side cutting can opener (I think, I can pull it out and look at it, my kid "Eagled", so it's been a while). Then I cut the bottom off another can AFTER cutting another 4 inch hole in the center. Next I measured out straight pipe enough to come out of the two holes CONNECTED BY a premade 90 degree turn. (think giant L). I used fiberglass batting as my insulator, it was free. If I made another I would put a support under the bottom of the L and the 90. Next from a scrap I put a ledge in the throat of the feed tube.

You make the circle cuts before removing the ends , to give it rigidity for cutting.

I sealed all edges with stainless steel flue tape. My Mistake was I used galvanised pipe, a big no no. But if it is outside and you burn it a lot with real hot fires keeping distance you will push off the zinc enough to be safe(I am told). We used galvanized steel garbage pails to make turkeys every fall in scouts, and no one has died so I believe this is safe. I added a grate top, for flat top cookery, this gents is extremely good at soups/stews/boiling water.

This does not pyrolize and just burn wood gas, you get ashes. If you only want to burn Wood gas, then bury the cold charcoal(negative carbon camping), you need a different stove.

You do use less wood and get less soot as you really get a very hot concentrated flame. Perhaps I will disassemble mine and show the thing off backwards , reverse engineer it replace the flue pipes and go forwards....

nice instructable...only improvement I can see, make an outer wall sealed up entirely, and leave 1 inch empty space. if it is nice and shiny it will reflect back some of the heat making this insulated and reflective and even more efficient. The outer sleeve if sealed and having minimum contact with the inner wall will be insulator and stop wind and cool air from cooling the inner sleeve/wall.

[andytompkins]

Some good ideas there... Would be great to see some pics of your stove.

[srilyk]

From what I understand, the wood is actually vaporized, and it's the wood vapor that burns. https://en.wikipedia.org/wiki/Wood_gas

[andytompkins]

I think there's four 'stages' to burning wood, and the gas is one of them. That's why you can burn wood but end up with charcoal and burn it again! I've seen rocket stoves that have wood packed where the insulation is in mine and they just burn wood gas, and you're left with charcoal. That's in theory, never really seen a good one of those working, more complicated.