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by Mark Schimmoeller

In October, 1995, I traveled for the first time to Santa
Barbara, Honduras, to begin a solar cooker project. It was
cloudy upon arrival, and the project shifted towards a simple,
yet effective stove that burns twigs or small scraps of wood.
Due to heavy deforestation, the cost of firewood rivals the cost
of food, forcing many families in Honduras to eat only tortillas
and not beans (Beans require much more cooking time). This stove
proved quite helpful to families there. With a typical wood
stove, a family in Santa Barbara uses one donkey-load of firewood
each week; with an Elbow Torch Stove (ETS) this same load of wood
lasts five weeks.

1. History & Philosophy

ASPI's philosophy is to use natural resources efficiently,
regardless of how abundant the resources may be. Hence, the ETS
ought to be used in the United States. For those in the United
States who cook with wood outdoors, this stove could save a lot
of time otherwise spent gathering wood. Additionally, much of
the wood that would normally be used for cooking could be left to
decay, adding humus to the soil. This stove could replace the
outdoor grill, costing less and polluting less. A small ETS is
ideal for camping trips, especially when a lot needs to be cooked
with a small amount of wood. One practical approach is for
campgrounds across the country to replace existing fire pits or
grills with Elbow Torch Stoves.

The ETS is an adaptation of the Rocket Stove, invented by
Dr. Larry Winiarski while working at Aprovecho Research Center in
Oregon. A stovepipe elbow is the crucial component of Larry's
stove. Aprovecho has Rocket Stove plans, which show how to build
a similar stove using an existing elbow or fashioning an elbow
out of tin cans (which lasts about one month). This technical
paper is a supplement to Aprovecho's, showing how to fashion an
elbow using two flat pieces of thick stovepipe metal.

Essentially, the ETS consists of an elbow that is placed in
some kind of outer structure and insulated with wood ashes, or
some other low-mass insulation, such as pumice rock, vermiculite,
or loosely crumpled aluminum foil. A fire is built in the lower
end of the elbow and food is cooked on the top end. Since the
elbow is insulated with a low-mass material (which doesn't rob
the stove of heat) there's an excellent natural draft; the fire
burns so hot (above 1100 F) that it almost completely burns its
fuel and is virtually smokeless.

The Elbow Torch stove functions according to these
principles:

1. The insulated elbow creates a natural draft which keeps
the fire burning hot.

2. The low-mass insulation encourages most of the heat to
go directly to the cooking vessel.

3. A metal skirt around the cooking pot quickly heats the
pot's sides as well as its bottom.

4. The elbow regulates air flow into the fire.

5. A shelf placed in the lower end of the elbow accelerates
the draft and keeps sticks off the ashes.

2. BUILDING THE ELBOW

The elbow described here has a horizontal length of 14 in.,
a vertical length of 18 in., and a tube diameter of 7 in. This
is the largest elbow that ASPI recommends building. The size of
the elbow is important because it affects the flow of air into
the fire. Too much air, or too little, will cause the fire to
burn cooler and less efficiently. ASPI recommends that an elbow
be made in either of the following two sizes: a large one like
the one mentioned above, or a small one, useful for camping, with
4-inch diameter tubes, a horizontal length of 6 in., and a
vertical length of 10 in.

To make a large elbow stove start with two pieces of thick
stovepipe metal (that can be bent by hand), one piece 24 x 18 in.
and one 24 x 14 in. The 18-inch piece will form the vertical
tube and the 14-inch, the horizontal tube. Rolling these pieces
up along their 24 in. lengths makes tubes with diameters about 7
in. First, cut these two pieces as shown in Diagram 1.

The 14-inch piece, which will be the horizontal tube, needs
to be cut 1 in. less (6 in. instead of 7 in.), to allow it to fit
into the vertical tube. It's important to keep the extra metal
cut from the 18-inch piece. It will be needed later to make a
shelf for the firewood. Note: In making the small elbow stove,
decrease the areas cut out of the tin sheets. To make 4-inch
diameter tubes, shorten the lengths of the metal pieces to about
12 1/2 in. instead of 24 in. The widths should be shortened to
6 in. and 10 in. The height of the areas cut from these pieces
becomes 4 in. for the 10-inch piece and 3 in. for the 6-inch
piece.

Once the cuts shown in Diagram 1 are complete, make flaps by
bending the tin over along the widths of both pieces, as shown in
Diagram 2. The smaller piece should have 1/2 in. flaps. On the
larger piece the flaps should be slightly smaller - about 3/8 in.
Wider flaps on the small piece produce a slightly smaller
diameter, allowing it to fit easily into the vertical tube. The
two flaps on each piece must be bent in opposite directions.
They should make a gap wide enough for the tin being used.

The next step is to use a convenient metal tube (an old
water pipe works well) for forming the tin pieces into pipe
shapes. Place the metal tube close to and parallel with one of
the flapped sides of the tin. Then bend the tin over the tube
slightly. Move the tube away from the flap a little and again
bend the tin over slightly. Continue this bending process across
the 24 in. length of the tin (at the midpoint the tin can be
turned over and the bending process started from the other side)
until a pipe is formed. Take time toward the end to work the
metal so the tube is nicely rounded and the side flaps hook
easily into each other. It's important that they easily hook
together - this is just a matter of bending the metal correctly.
Try giving a little extra bend to the flapped sides so they meet
each other straight on and not at an angle.

Once the tin pipe is hooked together, slide it over the
metal tube used earlier, with the joint of the stovepipe tube
facing up. Grip one end of the joint using vicegrips, if
available. Then start hammering at the other end, both against
the folded part of the joint and directly on top of the joint.
Remove the vice grips when the hammer reaches that end. When the
joint is tight, use the other end of the hammer and crimp the
joint as shown in Diagram 3. Repeat this process with the other
piece of tin. Now there are two tubes -- notice how they will
fit together to make a right angle elbow. The short tube is the
horizontal section and the long tube is the vertical section. To
join them, some bending will be required on their angled sides,
as shown in Diagram 4. On the vertical tube, use pliers to bend
a 3/8 in. flap inward along only the top third of the tube. On
the horizontal tube bend a 3/8 in. (roughly) flap outwards along
the perimeter of the tube. Increase the size of the flap (and
the degree that it is folded) towards the bottom so that at the
very bottom (where the joint is) the flap is about 3/4 of an in.
and bent back more than 90 degrees.

To join the tubes, fit the horizontal tube into the vertical
tube. Before doing any hammering, take a look at how the tubes
meet - more bending on the flaps may be needed. Sometimes
pushing in the sides of the horizontal tube helps it to more
cleanly meet with the vertical tube.

When ready, get the top part hooked together (the only part
that will hook at this point) and then turn the elbow over so the
top of the vertical tube is resting on the ground. Make sure the
top of the elbow (the part being hooked together) is still in
place. Then hammer the joint of the vertical elbow (it should be
sticking out above the horizontal tube) so it folds over the
joint of the horizontal tube. Fold over as little as possible so
the elbow angle doesn't change too much. (The stove will still
work fine if the elbow angle is slightly more than 90 degrees.)

The two tubes should now be secured by bending the vertical
tube over the horizontal as shown in Diagram 5. The horizontal
tube may have to be hammered more deeply into the vertical tube
so vertical tube is able to be folded over the horizontal tube.

3. Completing the Stove

The hard part is finished. Now what sort of outer container
to put the elbow in must be decided. There are many
possibilities - - metal, thick wood, bricks, or rocks. If a
small elbow is made, it could be put into a 5-gallon metal drum.
Even a cardboard box could be used for demonstration purposes,
but this isn't recommended. What is important is to have a
container big enough to allow for at least 2 in. of wood ashes
(or other low-mass insulator) surrounding all sides of the elbow,
even the bottom.

Look around and see what is available. It doesn't have to
be perfect. An old metal trash can turned upside down makes a
fine ETS, particularly with an elbow slightly smaller than the
one described here. In this case, so that a lot of ashes are not
used, fill the bottom of the can with rocks (or make a false
bottom somehow) to a point 2 in. or more below the horizontal
portion of the elbow. To get the rocks and ashes (and the elbow
for that matter) into the can, the original bottom of the can
(the top of the elbow torch stove) will have to be cut out (save
this piece). Measure where the elbow needs to go, then cut a
hole in the side of the can. Place the elbow through the hole,
fill the rest of the can with ashes, then cut a hole in the top
piece and work the top of the elbow through it. Now a grill is
needed to go across the top. An important thing to remember is
to maintain a 1 1/2 in. air space (1 in. with a small ETS)
between the cooking vessel and the elbow top. If the pot is put
directly on top of the elbow, the fire won't have an adequate air
flow.

Now take the curved piece that was cut out of the 18 x 24
in. sheet of tin and make two cuts in it, so it will slide into
the horizontal tube about a third up from the bottom; the width
of this piece will be less than 7 in. This makes a shelf for the
firewood, which is placed on top. Finally, make a tin shield on
at least three sides (the same height as the cooking pot) that
will surround the cooking pot and allow its sides to heat up more
quickly. If wood ashes are used as insulation, be sure the stove
is protected from rain.

To cook, place small pieces of wood on top of the shelf (in
the lower tube) and light a fire. Push the wood into the fire as
it burns. We think it's best to feed the fire so it stays within
the elbow - if it shoots out above the vertical tube, it will
smoke more. Happy cooking!