Making an Efficient Portable Wood Stove.

This stove is based on the plans for the "EverythingNice" stove which can be downloaded freely from the World Stove site: http://worldstove.com/album/your-versions-of-the-everythingnice-stove/

I have played around with fires and stoves over the years, and the World Stove design impressed me. I think the small opening in the top of the stove is an important feature and I saw this for the first time at World Stove.

I like the idea of stoves like this which create charcoal as a by-product. In the past I've used charcoal for blacksmithing, but in recent times I have been reading wonderful things about producing charcoal and mixing it with soil. For readers which haven't come across this idea here are the alleged benefits:
- By creating charcoal we are locking up carbon for a long time.... for hundreds or maybe a thousand years. Done on a large enough scale, this could help to reduce the problem of excess C02 and global warming. Even on a small scale it feels good to be doing it.
- It is said that charcoal in the soil can bring huge improvement to fertility. Evidently there are sites around the world where there is a lot of charcoal in the earth from previous generations of farmers. If you want to find out more you could do an internet search for 'biochar' and 'terra preta'.

Although I could just cook over an open fire, the stove could possibly allow the use of wood for a fuel where open fires are forbidden. Certainly the stove is safer than a fire on the ground (although precautions are still essential). And the fire in the stove, properly made and maintained, creates virtually no smoke. Furthermore, the stove is very fuel-efficient.

Sorry to ramble on, but before I explain how I made the stove here is a summary of how I think wood burns. When it is heated, certain subtances (the 'volatiles') are given off in a gaseous form. These create smoke and flame. Generally smoke is flammable, but to burn it requires a good mix with oxygen and it needs to be hot enough. So you could say that the flames are the smoke burning. Once the volatiles are largely driven off, what is left behind is charcoal. Charcoal also burns. It generally just appears to glow as it burns, but I understand that it also gives off carbon monoxide which burns with a bluish flame. Naturally in a wood fire you may have volatiles and charcoal both burning simultaneously, but for each piece of fuel wood the sequence seems to be that the volatiles mostly burn first.

For reasons that I am not totally certain about, if you restrict the oxygen (air) supply to burning wood, you can drive off and burn the volatiles without burning a significant amount of the charcoal. So if the burning process is halted once most of the volatiles seemed to have been burned, you can save the charcoal. The EverythingNice stove does this, well... nicely.

As with many things I believe you don't need to stick religiously to instructions to get useful results. But the instructions are a very good place to start.

The stove is made from two 'tins'. One sits inside the other. The smaller tin shouldn't be a lot smaller than the outer tin. The air which mixes with the smoke to allow it to burn is pre-heated as it rises in the gap between the tins, so the gap needs to be large enough to let the air flow at the right rate... but if it is too large, a lot of the air won't move close enough to the inner tin (the burning chamber) to be heated as much as it could be. The inner tin needs to be a little shorter than the outer tin so that the air can travel over the top of the inner tin to mix freely with the volatiles (smoke).

The hole in the apparent lid of the outer tin should be smaller than the diameter of the inner tin. This concentrates the smoke. I like to compare this to having a fire where one log often won't burn well on its own, but if two or three logs are burning close together they keep each other hot enough to keep the fire roaring. So what I'm saying is that the hot smoke particles are kept close together to stay hotter. I said 'apparent lid' because I don't believe that an actual lid on the tin is necessary. You could simply use an inverted tin can and cut the outlet hole in the bottom of the can. I haven't tried this yet, but I can't see why it shouldn't be successful. The ground the tin sits on creates the bottom of the stove in this case.

For my outer can I bought a stainless steel tea canister from The Warehouse for $7.99. It looked good and had a nice-fitting lid. The can does not have to be stainless steel to make a useful stove, but stainless should last longer. However stainless steel can be a pig to work with compared to ordinary tin cans.

The first thing was to mark where the air holes had to be drilled. The instructions say that the holes should be from 12 to 15mm in diameter and should go as close to the bottom of the can as possible. I marked a ring around the circumference using a felt pen held at the right height on a table while rotating the can:

The holes on my can were further from the bottom than suggested, but it gave me the option of filing the holes bigger, plus it created a lip which might help to hold in stray coals that found their way into the can. I wanted to drill 12mm holes, so I made marks around the circumference that were approximately 18mm apart:

I then centre-punched each mark to create an indentation to start the drill. To support the can while punching, I lay a heavy pipe wrench on the edge of my bench to create an 'anvil' to punch against. With the gentle hammer blows used in this case, the wrench didn't jump about too much, but care is needed:

I drilled the holes in three stages. I used an electric hand-drill and started with a drill bit maybe 4mm in diameter. Then I followed up with an intermediate-sized drill... then the 12mm drill. Great care is needed to ensure that you don't harm yourself with the drill. Drilling sheet metal at any time can be hazardous, but stainless steel is one of the worst things to work with. You can buy special sheet metal reamer-type drills which don't grab as much, but I used sharp, ordinary high speed steel twist drills at a relatively low speed. If you have to hold the can with one hand, wearing a sturdy leather glove is a good idea. If you have a vice, you could have a bit of wood protruding from the vice which the can could sit over while you drill. Safety glasses should be worn while using an electric drill. The edges of the holes will be bent, rough and sharp, and these can be hammered flat then smoothed with a fine file. A chainsaw file is good for this. If some of the holes end up a bit out of line it isn't the end of the world.


I cut the hole in the lid by first driving an old knife through it with a hammer against a block of wood. I made an 'x' pattern with the knife, then lifted up one of the resulting triangles so I could insert my small curved tinsnips to cut out the circle. The instructions indicate that this hole should be around half the diameter of the inner tin. If you don't have tinsnips, then maybe you could drill a ring of small holes and use a cold chisel to cut the webs of steel left between the holes (done while the lid is sitting flat against a soft steel anvil of some sort). Or if you are using the bottom of an ordinary tin can you could simply use a knife if you are careful. Safety glasses should be worn for this operation too.


I used a fruit can for my inner tin. I would have preferred a stainless steel can, but I couldn't find one. But the ordinary can was a pleasure to work with compared to the stainless. All you need to do with the inner can is to ensure it is the right size (cutting it down in length if necessary), and to make a ring of holes around it. The instructions say these holes should be 4 mm in diameter, and a formula is provided which gives the height for the centre line of holes from the bottom of the can. So you need to mark a line around the circumference of the can. The distance from the bottom of the can to the line is equal to the height of the top of the holes from the bottom of the outer can plus half the diameter of the air holes in the outer can. I simply pushed a sharp awl through the can to create these holes. It worked beautifully. I placed the holes as close together as possible around the circumference. I made the holes slightly larger than the awl by rocking the awl around when pushed right through.


Here are the three pieces which make up the complete stove. The only holes in the inner can are those in the one ring around the circumference (this inner can has no lid, and there are no holes through the bottom of either can). Also shown is the 'firewood'. This was gorse cut to a length of around 75 mm. The instructions imply that the fuel should not be stacked in the can higher than a certain point. This point is the same distance from the top as the holes are from the bottom:

There is blood on that firewood. I haven't cut myself with a hatchet for years, and I was taking a risk. I had a comparatively gentle reminder that I need to follow rules for safe wood splitting. Here is the wood stacked in the can:

I kindled the fire by laying paper and a few small slivers of wood on top. Lighting at the top is an important part in the operation of this class of burner. It should burn from the top down. I was very impressed with the results. I haven't done any serious tests, but this small stove appears to burn for maybe 20 minutes with one load of wood, so it isn't really big enough for my requirements (the current inner can is 75mm in diameter, and not very tall). I found that small bits of wood could be added successfully while the stove was burning well, but when I put in more wood after the volatiles stopped flowing, all I got was a heap of smoke until the new fuel got hot enough to ignite. I don't think that new fuel could be added indefinitely, because the charcoal will build up in the can, but you can get away with adding a few small bits.


The stove burned very cleanly, although it did blacken the bottom of the 'cook pot' as expected. The outer bottom part of the outer can remained comparatively cool most of the time, but it would be foolish to sit the stove directly on to flammable vegetation or other materials.

Here is the charcoal left afterwards. I tipped it into water to extinguish it. If I hadn't extinguished it it may have 'gone out' by itself, but it was glowing in some places. Note that the outer can doesn't have much discoloration, but you can see that the inner can has been really hot. There is also plenty of 'black' on the bottom of the pot.


I'm now keeping an eye out for larger cans to make a stove which will burn longer on one load of fuel. I'm inclined to think that although I could use cans which are slightly wider in diameter, it may be better to go for more height to make the 'top down' burning last longer, to ensure that the sides of the inner can stay relatively hot for heating the incoming air, and to ensure that enough air can reach the fire from the small holes through the inner can wall.


This is a great little stove. I wish to extend my sincere thanks to World Stove for getting me started.


Best wishes from Nelson, New Zealand.... Stephen Coote.

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Shrafter
Comment by Stephen Coote on April 19, 2015 at 18:05
Good stuff Kesate. You are re-igniting my enthusiasm for this type of stove. I look forward to the video. Thanks and best wishes from Nelson.

Shrafter
Comment by Kesate Iyasu on April 19, 2015 at 17:39

Stephen, i tried your interpretation for a kiwi styled coffee tin wood gas stove and worked a charm, instead of a tin, i tried with a 2 dollar s/s chopstick holder as they have predrilled holes ( although vertically so maybe a bit too much air ratio? ) but it does work. will upload a small video of it shortly.

Cheers Mate!

Super proud of my hori project!


Shrafter
Comment by Stephen Coote on October 30, 2010 at 5:55
Thanks Scott.... sounds good. I must check it out.

If this 'Nimblewell' burns for a while on a load of fuel, and doesn't smoke too much, it could be a very good thing.

Shrafter
Comment by Scott Hamilton on October 29, 2010 at 21:50
I really like my ' Nimblewell Nomad Little dandy' plans available at http://zenstoves.net/Wood.htm, do not use it a lot as normally out bush with Scouts and they carry gas stoves with them. Not the most efficient stove design but simple easy and pack down to nothing.Is this a Downdraft Gasifier stove, I have made one of these before and it is really bizarre dropping sticks into it, and seeing it turn to gas suck down and be burnt up at the top holes.

Shrafter
Comment by Mike on July 18, 2010 at 13:26
Awesome idea mate.Nice one

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