Juntos Stove

Paul Anderson February 21, 2002

This is my report on the February 2002 developments with the Juntos (Together) stove.

Since its inception a couple of months ago, the Juntos stove has been modified substantially to simplify it. It still is a "stack" of burners, etc. on top of each other, but now each burner or cooking unit or chimney unit can be individually removed without moving any other unit. This is because of multiple racks as you can see in the first and second photographs.

Picture 1 is below.

They are NOT grills nor grates. They are RACKS to hold units in place. The vertical (white) construction is cement blocks, but people could use bricks or hard mud or metal or stones or other materials (even wood if care is taken to not expose it to the flames.)

My Juntos stoves is inside a metal tool shed at my home. The temperature during the time of these photos was about 45 degrees F (about 12-14 centigrade). No wind because I am inside the shed (with the doors wide open.)

Picture 2 is below.

You are viewing a gasifier in the bottom level and an internally tapered chimney in the second level. More about the levels in a later message.

Picture 3 below show the seven gasifiers, of which I made six myself (except for the one on the far right end that fits into the metal box next to it.)

Pictures 4 and 5 (below) show the top and bottom of one gasifier made from a #10 tin can with an outer metal "jacket" for pre-heating secondary air.

untos (Together) stove -- Part 2 (text message) Written 21/Feb/2002.

It is called the Juntos (which in Portuguese and Spanish means Together) Stove because different aspects came from different sources, and we bring it together in this stove.

You should have received the previous message with the 6 pictures included.

Mostly I am burning standard "pellet stove" pellets of compressed sawdust. Great fuel. I have burned other biomass with good success, including yard waste, and locust tree pods, and briquettes mainly from paper pulp and sawdust/wood shavings. The briquettes are intentionally broken into pieces (to gain surface area) and do not last as long as the pellets. I am still working on better briquette-type fuel for the gasifier.

As shown in picture 3 I have experimented with about 7 sizes and variations of gasifiers. ALL of them do work. Problem of the smallest (a typical soup can) is that a gust of wind can easily extinguish the upper (secondary) burning. To avoid that, an attached permanent chimney would be beneficial. That chimney would also make the unit as tall as the others, so that it would nicely fit into the same vertical space in the lower chamber of the stove.

Term: A "stove" can have burners (plural and of various types), chimney, chambers (to place the burners) and assorted ways to transfer the heat to the cooking pot or cooking device. Some have very few, some have a lot of pieces. The word "stove" is generic and is NOT descriptive of all the different ways people think of stoves.

Natural convection gasifiers of the IDD (inverted downdraft - Reed-Larson) type do work VERY well. Basic construction is seen in Pictures 4 and 5.


1. Tin can that only had the top removed. Diameters and heights give different characteristics of length of the burn, etc.

2. Air pipe made from a length of pipe about 20 cm (8 minches). I use aluminum in part because I had pieces laying around. You do not need thick stuff. One gasifier has a pipe cut from a leg of an old folding lawn chair. One gasifier has a square-bottom “U” bracket that was pounded together at the top to make a triangular pipe. That one was too small, but triangular pipe might be very viable in some situations, especially because the “Karla Key” (discussed below) makes a nice triangular hole for inserting the triangular pipe.

3. Two screws (I use self-tapping metal screws) long enough to go through the bottom of the tin can and into the pipe. I like at least one of the screws to be long enough to go all the way through the top-side do the pipe and actually screw into the metal grate.

4. Metal grate (see pictures to see a nice size of holes). I went to the junkyard and ripped a perforated metal cover (about 80 by 80 cm = 32x32 minches) from something. It is soft steel and I can cut it with decent tin-snips. I draw on it the diameter of the tin can and then another circle (or odd shape) about 2.5 cm (one minch) bigger. I cut the outer circle, and then cut in a radial way inwards to the inner circle, creating tabs. Then I bend (by hand with gloves and pliers) the "tabs" so that they help support the grate horizontally when it is eventually pushed into the can until it rests on the top of the air-pipe. Note: No tab on the part that is to sit on the air pipe.

5. Outer jacket. Metal. From another can, or from sheet metal or from stove-pipe or whatever. It must have about one cm (0.2 minch) of space (let's call it a "gap for secondary air") on all sides of the tin can. Too much space and too little space are not good, but about a cm seems about right. (I do not measure it; I do it by "eye-ball".) The outer jacket must allow air to enter in from the bottom, and it is good (I think, but have not tested) if the gap is not open at the top end. More in the construction notes below.

Tools for the gasifier construction:

1. Hammer (or a nice rock that fits your hand well)

2. Tin snips

3. Screwdriver (or nut driver if you have hex heads on the screws)

4. A "Karla Key" which is actually a can-opener of the type that makes a triangular punched hole into a closed tin can. (commonly known as a "church key" or a beer can opener before the advent of tab-tops, etc.) Named after Mrs. Karla Weldon. The real Karla Key has a screwdriver at the non-punch end, replacing the need for item #3 above. Karla Keys should be made in different sizes, especially for the "reach" of the triangular punch point being increased to make holes further in, that is, not so near the edge where the punch grips the side of the can.

5. One hack saw (the blade is the important part.)

6. Yes, a power drill. I am sure it can be done without the power, but I am trying to save time. I use it to drill 2 holes in the bottom of the tin can and into the air pipe, so I can drive in the screws more easily. I can also use it to make holes in the outer third of the air pipe (think of them like holes on a simple reed flute.) Sizes not yet determined, but about 2 - 3 mm ( about 1/10 minch) in diameter. Some of my air pipes do not have any of these flute holes because I let the primary air enter the outside end of the air pipe.

7. (An extra tool for other jobs is listed here, but actually I made my own.) I made a nice hole- punch by doing a diagonal cut (by hack saw) on the end of a piece of pipe maybe 15 to 20 cm long with about the same diameter of most of my air pipes, about 2 - 3 cm of diameter. Best if it is steel or iron, but seems to work with aluminum too. Good to have a sharp-ish point. I use it by hitting the other end with the hammer or rock. I might make several of these with different diameters.

Assembly: (Seems to be different each time I make one, so this is not Gospel).

A. Prepare the air pipe. I like a 45 degree or more shallow angle on the inside end of the air pipe. Outside “flute-type” holes are optional, or can be added later.

B. Punch a hole (with Karla Key) into the side of the tin can near the closed bottom. Avoid the area of the seam of the can. Or you can use the home-made punch, or even use the air pipe itself. This should result with the air pipe very close to the bottom of the inside of the can.

C. Push in the air pipe, trying to NOT make a big hole around it. No space for air leaks is best, but really not too important if the fire is to be on "high" with plenty of primary air. Besides, some mud or furnace putty or other stuff (foil rap, etc.) will effectively plug the hole if it is too big. Push the air pipe until it is about half way across the bottom of the can. I like to have the diagonal cut turned downwards because it could help spread out the primary air. But that is not confirmed as being important.

D. Drill 2 holes appropriate for the 2 screws to grip the can bottom and the air pipe. A long one only needs to start coming out the top side of the air pipe.

E. Insert the grate, circular in format, supported by the tabs, snuggly fitting, beat it into place to rest on the air pipe (No tab at the air pipe, right !!)

F. Continue with the long screw(s) that self-tap into the holes of the grate. Make it snug. Pick up the unit by the air pipe and notice how much the air pipe is like a handle. (Do not smoke it, but it sure looks like Popeye's pipe from the cartoons.) Yes, the air pipe IS the handle, but caution about it becoming hot at the late stages of the gasification burn -- especially if it is aluminum.

G. Around the upper lip of the up-right can you are to make a ring of holes for the secondary air to enter the can. Use the Karla Key. Makes no difference if you punch inwards or outwards, but outwards leaves no pointy things sticking inside. Be careful you do not dimple the can too much. Yes, you can use a power drill. My holes with the Karla Key are triangles about 5 mm on each side. Number and size of the holes is a topic for someone's thesis. I just put in what I think seems reasonable, depending on the size of the can.

H. The jacket and the resultant gap can be pretty or not, just so it is functional. The easiest jacket is another can slightly bigger in diameter. You can cut out both ends, but you could also leave the jacket can with its bottom intact, but you will then need to put in the air pipe after the 2 cans are together. You WANT air to get into the gap at the bottom of the jacket, so leave notches as seen in Picture 5. Or if you have a bottom on the outer jacket can, then use the Karla Key to punch holes into the lower SIDE of the outer can, as can be barely seen in the lower side of the 6th gasifier from the left in Picture 3. I like this because the triangle pieces from the Karla Key punches act as spacers to maintain the gap at the bottom of the joined cans.

I. To finish, you need to do something about the upper end of the gap. Picture 4 shows tabs bent over from the jacket to the inner can. Sometimes I have plugged the gap with aluminum foil. Some gasifiers (like the 4th one from left in Picture 3) have a jacket of aluminum “dryer hose” or some such name. Nice stuff for experimenting. I got it at the Menards (Home Depot type store). It is rigidly stretchy ( ) and then I bend in the top part to close off the gap. I bought 3 diameters, so I will someday make a 10 minch (25 cm) diameter gasifier with whatever height I want. (Oh, I forgot to tell you that I probably made another 5 or 8 gasifiers that either did not survive to be photographed or were too ugly to be recognized as a gasifier.)

Hey, the gasifier is finished. Total costs are very low, but the life span is not what I was after in the experiments. Do some good design work and use quality new materials and you could make some really expensive gasifiers. Below I discuss how this thing works, which is what is important to me.


See Picture 1. The spacing of the racks is made to match the heights of the components. What is shown is set for the larger gasifiers like a #10 tin or a paint can. When in use, because of the rack, there is about a 5 to 8 mm space between the top of the gasifier and the bottom of the next unit above it. That does not seem to be a problem, and might even be mandatory to ensure sufficient air entering the bottom of the intermediate level units.

In previous messages I described how I light it very easily (sawdust and wood shavings mixed with torch fuel (like kerosene?). One match almost always does it.

A very important element is the chimney effect. I get that by placing a cylinder (can with no ends) over the functioning gasifier. This can be in the stove, or away from the stove where you can use a taller chimney. When in the stoves with its racks at fixed heights, if I want more chimney, I put another can on the next higher rack, like the smaller diameter can seen in Picture 1 behind the flame.

The chimney can in Picture 2 is special because it has in inner taper to funnel upwards the flames to a smaller hole than at the bottom. Picture 2 shows that I could benefit by an even wider diameter chimney at the lower end. Picture 1 is NOT just a “best shot” picture. The flames stayed like that while I fiddled with the camera. Without a chimney, the flames will flicker as is seen in Picture 6.

Cooking: With Noeli, Sarah and Ed, I have now cooked a macaroni meal, boiled water, cooked hot dogs in water, made porridge, and fried an egg. I know that I could have multiple gasifiers working at the lower level, and have plenty of heat above. Additional variables to be considered include:

A. Diameter of the gasifier

B. Height of the gasifier

C. Amount of fuel

D. Type of fuel

E. Control of primary and secondary air.

But there is more to it than that.

Please remember that this is the JUNTOS STOVE. It is TOGETHER, and thus far it I have focused on the Reed-Larson gasifier with the Anderson air pipe (Paul’s pipe) and the Karla Key and some burning of briquettes. There are more contributions included:

Think of the Juntos stove (as shown in the pictures, and as it might become eventually) as a multi-layered stove. Three layers are shown in Picture 1: Gasifier at the bottom, then the middle layer (with the chimney in place), and then the top layer (for the pot or for more chimney or for whatever). It is the WHATEVER that is important. Here is my list of units that can be in the middle or top layers, sometimes functioning WITHOUT a gasifier below them:

1. Chimney unit

2. Intermediate flame unit (IFU) (to be discussed)

a. Open side, ala Rocket Stove,

b. Closed sides

3. Char-burning unit

4. Cook-pot unit (directly above the gasifier)

5. Insert a gasifier WITHOUT as gasifier below, OR with a gasifier below that has its heat ducted to not come under the gasifier in the middle level, that is, with a unique small chimney.

6. Fuel-drying unit (does not burn the future-fuel), could be on a 4th or 5th level of the racks of the stove.

7. Weldon Window (to be discussed)

8. Water heater

9. Oven, griddle, plancha, other ways that people like to cook, all treated separately from the issues of the fuels and the ways that they are burned.

Results of experiments:

A. Intermediate flame units (IFU): In its simplest form, an intermediate flame unit (IFU) is a can that holds fuels and sits on a layer (or two) above a gasifier. Therefore, it has some openings in the bottom. My nicest one had holes simply punched with the previously described home-made punch from a piece of pipe. The punch leaves a pointed tab facing inward into the IFU can, thereby available to support the fuel and thus helping the flow of air into the can under the fuel. The holes in the bottom allow the heat and air and other stuff from the gasifier to enter into the bottom of the intermediate flame unit. This helps light the fuels quickly (therefore with less smoke from the IFU). “Regular” combustion occurs in the IFU, and the fuel goes from fuel to ash, with no saving of char, etc.

If the IFU has an LLL (Low Lateral Loading) side opening into which fuel is pushed, it is quite similar to a Rocket Stove. It will roar with flames. Thank you Larry and Dean and Aprovecho for this nice aspect of stoves.

If the IFU does not have an LLL opening, it can only be fueled from the top. Here is where you place a nice briquette inside. Be sure it stands up vertically and can get air from below to its center hole. Within a very short time being placed over a functioning gasifier, this briquette has a beautiful flame coming up that center hole, and can also get nice burning on the outside of the briquette. Thank you Richard Stanley and Legacy Foundation for being champions for the briquettes with holes. When the briquette is dying down, grab the intermediate flame unit (IFU) by its handle or with tongs or with good gloves. Pull it off of the rack, drop in another briquette and place it back into burning position above the gasifier. How about 10 seconds to reload the briquette burner? Maybe less time. Certainly not very disruptive to the cooking process.

Better IFUs could have some air controls at the bottom or lower sides. Also, when the IFU is burning, the cook can remove the gasifier (while the IFU continue the cooking), can empty the char from the gasifier, re-load the gasifier, re-light it easily (draft will be strong above the gasifier), and continue. Or, simply put an empty can under the IFU to catch the ash that will fall down.

The name of the game is CONTROL of the amount of heat needed by the cook. Not as simple as a thermostat controlled burner on a modern fancy stove. But much much more control than what cooks in developing countries have had in the past. And it is with biomass fuel.

B. The Weldon Window. Bob Weldon is a very good friend of mine. When he came to see my early efforts to place a Rocket stove on top of a gasifier, he simply said. “When the fire in the Rocket Stove dies down, you can put a pot into the hole and cook with the heat from the gasifier.” Well, my hole for sticks was rather small (as appropriate for a Rocket Stove), so I enlarged it and started putting pot-type stuff in it. Well, the opening needs to be pretty big, so the Weldon Window is actually like putting a pot into the chimney. You can close the window, or you can let the pot block the window hole, or do not even worry about blocking the window. And, because the Weldon Window is actually part of one to the types of units to slide onto and off of the racks in the intermediate level or even on the top level, it can be easily removed from the vertical column of fire and heat, checked for what is cooking, stirred, seasoned, returned to the fire, etc. Thank you Bob Weldon for a nice addition to the Juntos Stove project.

C. Interchangeable parts: With the above units, we can have fires ranging from major heat (as with a gasifier on full, with one or even two IFU stacked on top of it) down to simmering with low heat from charcoal (produced in the gasifier from biomass) or with low primary air to the gasifier, or on small diameter units, or on larger units with variations of types of fuels for high or low heat. A functioning gasifier under a blazing intermediate fuel unit (IFU) can be removed and placed under a different pot that needs only low heat.

Also, when the gasification stops (and only charcoal remains), the gasifier unit that has the following characteristics: The air pipe becomes hot all the way to the outer end because the charcoal is sitting on the grate that is touching the air pipe. But it does not smoke when it stops gasifying because the fumes go up into the IFU above it. The gasifier can be easily removed, and the hot charcoal can either be used in a charcoal burner or be placed in an air-tight container (a paint bucket works beautifully, thanks Dan Dimiduk) to be totally extinguished in a few minutes, but dry and ready to be burned later.

We need to see the Juntos Stove as being highly flexible. We are really dealing with “combustion units”, that is, how to get the heat when and where we want it. The highly related issues of fuel types and cooking preferences are important, but that is where localized variations are allowed, tolerated, encouraged and essential.

Note: Let’s be serious. ALL of our innovations are not so 100% new. Gasification, briquette, stick in wood from the side of a fire, stacking on of chimney segments, have an air pipe, open a window to put a pot into the chimney, etc, etc were not first invented by anyone alive today. Ancient people probably did such things in many different places at many different times and may or may not have even understood what they did. We are today dealing with some refinements (maybe), but especially we have better understanding of the processes and the objectives and how to accomplish the goals. And there are still numerous additions to bring TOGETHER in the Juntos Stove. We all await the contribution of others. And I can hardly wait to hear how Crispin and the REAP people and Larry and other “engineer-type” people can take “tincanium” stoves to better levels. Also, EVERYTHING needs testing at the same time that we are taking the stoves to the people who need them NOW.


So, some of you wanted to know about the Juntos Stove. Some said they will do some testing of it. Sorry, none of my tin cans are currently for sale.

But why would you want a gasifier or a total Juntos Stove from me? You can certainly make your own and replicate all that I have experienced. Please make it and please test it and please tell us about your experiences. I will try to be helpful. But on 5 to 30 March I will be in Africa and e-mail messages are more difficult to make and send from there. I can read them but not answer easily.

Good luck.

It is fun doing stoves work Juntos (Together) with you.


February 21, 2002

Air Force 1