Wood Conserving Cook Stoves A Design Guide 1980 PDF
Wood Conserving Cook Stoves A Design Guide 1980 PDF
Wood Conserving Cook Stoves A Design Guide 1980 PDF
--,
A VITAIITDG PUBLICATION
Front cover: "The Wood Gatherer,"
an original woodcut by VITA
Volunteer Rosemary Feit Covey.
Available in a limited edition of
signed prints on Japanese rice
paper. $25.00 (US) each plus
$2.00 (US) postage and handling.
Proceeds from the sale will sup-
port VITA's publication efforts.
ISBN O-86619-000-7
...
111
Contents
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..e.. vii
Introduction . . . . . . . . . . . . . . . . . . . . ..*...................... 1
1. HOWTO USE THIS BOOK . . . . . . . ..m........................
2. HOWSTOVES WORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
How wood burns ........................................ 9
How heat is transferred ............................... 12
Conduction
Radiation
Convection
How heat is contained ..*..*..............a............ 15
Stove components
Traditional stoves
Simple metal stoves
3. HOWTO MAKE STOVES EFFICIENT . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Conserving heat . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*......... 29
Energy losses in stoves
Improving combustion efficiency
Using the heat from the gas stream
Minimizing heat loss from heating the stove
Minimizing heat losses from pots and stove walls
Improving traditional stoves .......................... 33
Combustion chamber engineering
The chimney-and-damper approach
Improving combustion efficiency
Improving stove building materials ................... 47
Cast iron, steel plate and sheet metal
Ceramic
Mud and brick
V
4. HOWTO BUILD FOUR STOVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Lorena stove . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..a........ 55
Materials
Tools and equipment
Construction
Use of the stove
Smokeless chula . . . . . . . ..I.....................*....... 71
Materials
Construction
Use of the stove
Singer stove ......................................... 83
Materials
Construction
Use of the stove
Sawdust cook stove ................................... 94
Materials
Tools and equipment
Construction
Use of the stove
5. HOWTO USE STOVES EFFICIENTLY . ..o.................... 99
Choosing wood . . . . . . . . . . ..e........................... 99
Using wood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Dictionary of Terms ..................................... 105
Bibliography ............................................ 109
vi
Acknowledgements
This manual has been made possible by a grant from the al
Dir'iyyah Institute of Arlington, Virginia, and Geneva,
Switzerland.
VITA volunteers and others who reviewed the book for technical
accuracy include Nancy Axinn, Dr. Norman Brown, Dr. Gautam
Dutt, David Hughart, Dr. Larry Icerman, and Jeff Wartluft.
vii
Introduction
The costs of using firewood in traditional ways are growing
every day. Fuelwood is the primary source of energy for house-
holds in developing countries (Openshaw, 1974). It i!; used
mainly for domestic cooking and, to a lesser extent, for heat-
ing and industry.
Population pressure in many areas has made the demand for fire-
wood consistently exceed the supply. The consumption of wood in
Nepal is seven times greater than the annual forest yield. The
price of firewood in Kathmandu has tripled in three years
(Karki and Coburn, 1977).
For the cook and the cook's family, the problems do not end
once the firewood is gotten. Smoke from open fires and inef-
ficient stoves can create a dirty, unhealthy situation. Eye and
respiratory problems are wide-spread. Burns and scalds--
1
2
The reason for the lack of data seems to be that planners have
for years assumed that people advanced from wood fires to an
electric or gas range, not to an improved wood-burning cook
stove. It just was not considered necessary to think very hard
about a better cooking system based on wood usage.
It should be noted clearly that the reason for moving from wood
stoves to cooking systems based on other power sources--in the
areas where this has occurred over time--was that these other
sources became more feasible. They were efficient, clean,
seemingly abundant, and cheap. Today, the state of the world
suggests that wood-burning systems, at least improved ones, are
a more attractive alternative for some applications than was
once thought. The interest in many developed countries is in
wood stoves for space heating. The emphasis in less
industrialized countries is on improved cooking stoves, the
subject of this manual.
perhaps the most basic design comes from India, where much work
with cook stoves was started with the interest of Mohandis
Gandhi in programs for rural areas. The major research result
in India has been the Hyderabad Engineering Research Laboratory
chula, better known today as the HERL chula. Chula (also
spelled "chulah") simply means cooking place. The HERL chula
was based on traditional Indian fireplaces, and adapted by
S.P. Raju, former director of the Laboratory. Many stove
designs being promoted throughout the world today are based on
the HERL chula.
The Lorena stove is built from a massive sand and clay block,
while the Singer stove is assembled from smaller blocks. The
description of the Lorena stove begins on page 55. The
description of the Singer stove begins on page 83.
page 94.) The practice is not new. Such materials have been
used for some time. In Upper Volta, for example, millet stalks
are burned almost exclusively for six months of the year. Wood
is used the rest of the time. In south Asia, cakes of cattle
dung are used as a fuel supplement.
7
2. HOW STOVES WORK
Fire is so important to human health and comfort that for many
years the Greeks and others thought it to be one of the basic
elements of the universe. We now know that fire comes from a
source of heat applied to fuel in the presence of air.
Heat sources can be the sun, its rays focused on the wood, or
the flame from a match or flint. The fuel in this case is
wood. Wood is made mostly of cellulose, lignin, water (HzO),
resin, and other materials. Wood is an organic substance; it
once was a living thing.
When heat is applied, the surface layer of the wood gives off
water, carbon dioxide (C02), and some organic acids (see
Figure 1). The carbon dioxide and the water vapor cover the
surface of the wood and prevent oxygen from coming into contact
with the wood. This results in smoke but no flame.
Each gas requires a certain amount of air and must reach a cer-
S tain temperature before it will ignite. The greater the amount
of air, the more heat the gases will carry away. But the wood
Will not ignite if the proportion of excess air exceeds a cer-
tain limit. In this case, there are too few chemical reactions
9
10
11
Once ignited, the gases burn with a luminous flame. The heat
continues to drive more gases from the wood until only carbon
monoxide and hydrogen are given out. The charcoal merely glows
with little or no flame.
When the burning 'process goes quickly, a lot of tar and highly
flammable gases are produced and a lot of heat is freed quick-
ly. Little charcoal is produced in that case. If burning is
slow (for example, if there is little air and little heat near
the wood surface), then more carbon dioxide, water vapor, and
charcoal are produced. Heat is given out at a much slower, more
constant rate.
12
Conduction
Conduction is the passage of heat through a substance, from a
hot area to a cold area. If one end of a substance is heated,
that hot end contains more energy than the cold end. This
energy difference is transferred through the material via the
motion af the atoms in the substance.
Radiation
All bodies above absolute zero temperature give off energy i:?l
the form of heat radiation. When heat radiation comes into con-
tact with a solid, it is reflected, absorbed, or transmitted to
the solid.
rf8
Convecrion
Figure 2
14
Convection
Convection involves the transport of heat by the movement of
some sort of fluid, such as air or water.
Stove components :
. Smoke from the fire can cause or worsen eye and respiratory
problems, and can leave cooking areas black with soot.
around the fire. The top is covered with some kind of grating
upon which the pot is placed. While this does not help a great
deal with the smoke problem, it can result in substantial fuel
savings.
I firebox
. flue or chimney
/I,cF. air inlet
3
i' - one or more dampers
JC
'L-/ . baffles
. heat exchangers
Firebox
The chamber in which the initial combustion takes place and the
fuel is burned is the firebox. Some stoves may also contain a
secondary firebox where many of the gases produced by the ini-
tial combustion are burned. There should be no uncontrolled
points of entry for air in the firebox.
Chimney or Flue
A metal chimney will lose heat faster, and thus be more prone
to a creosote buildup than will a clay or masonry chimney. Gal-
vanized metal is preferred over blued metal by some people. In
some places, work has been done with a material that might be
called "ferromud" --a form made of chicken wire, plastered with
clay to form a strong chimney. "Ferromud" may be significantly
cheaper than either metal or clay chimney pipe.
Air Inlet
The fuel must have oxygen to burn. Air is fed into the firebox
through an air inlet and then sucke ythrough the fuel by the
draft created by the flue or chimney. Because a strong draft
causes a hot fire, an efficient stove will have an adjustable
opening to allow the cook to control the rate of burning, and
thus to control the temperature.
Dampers
Baffle
Baffles can also be placed in the flue. Here they will help
keep the hot gases near the second and third pots. More heat is
transferred to the pots. The food cooks more quickly.
ITDG has done tests that show that baffles can decrease wood
use by 50 percent when placed correctly.
.
Heat Exchanger
Traditional stoves
Three Stones
The most basic, and one of the most common, wood-burning cook
stove is simply three stones arranged on the ground in a tri-
angle (see Figure 3). Use of this stove differs from region
to region. One of the more efficient ways of using it will now
be examined in detail.
20
Figure 3
Chulas
Figure 4
A widely used chula that burns scrap wood and straw (see Figure
5) is found in Bangladesh. This stove is constructed in the
ground and consists of two holes linked together. Around the
larger hole are ;ithree raised points on which the pot is
placed. Scraps of, wood and waste are placed in the hole and
lit. Air is drawn down the hole and mixes with the fuel. The
flame and smoke are drawn up through the space between the pot
and the pot stand.
//n’EE Flgure 5
the large hole and sits in the bottom of the stove. Visual
observations indicate that only part of the incoming air is
actually drawn down to where the wood is burning.
Figure 6
Kamado-style Cooker-
Figure 7
25
Rice hulls or sawdust are poured around and over the two sticks
and packed firmly with a block of wood. The chamber is filled
to about 5cm (2") from the top. The two sticks are carefully
removed, leaving a tunnel through the fuel from the air vent to
the top.
Figure 9
Figure 10
Figure 11
27
Stove-in-a-bucket
Figure 72
3. HOW TO MAKE ST VES EFFICIENT
The efficiency of a stove depends on many factors, from the
design of the stove to the type of fuel used. This section dis-
cusses the ways in which energy losses can be reduced by
improving the designs and the materials of traditional stoves.
Conserving heat
29
30
. Losses to the atmosphere from the stove walls and the cook-
ing pot. Any hot object will radiate and conduct%heat to
anything cooler around it.
Figure 13
31
. placing the pot away from the seat of the fire. The most
efficient position for the pot is where the flame is not
cooled by the pot's cold surface, but where the bottom of
the pot still receives a large proportion of the radiant
energy released from the fire;
Figure 14
Figure 15
32
Figure 76
The amount of heat lost from a stove depends on the outer wall
temperature of the stove and the speed of the air flowing past
the stove. The closer the stove wall temperature is to the sur-
rounding air temperature and the lower the speed of air flowing
past the stove, the lower are the losses. Heat losses from
'. stove walls can be lowered with some stoves by a double wall or
brick lining.
In field tests Openshaw found that this Thai stove took half as
much charcoal to boil water as the metal equivalent.
Dr. de Lepeliere's metal stove-- This stove was designed for use
in Africa. The stove was initially constructed from metal. It
has an inner combustion chamber that slopes at a 45O angle. The
36
Figure 16
The air enters through the outer casing and absorbs heat from
the hot inner chamber. This preheated air then enters through
the inlet holes around the fuel, The incoming air serves
effectively as an insulating layer between the combustion
chamber and the outside. The heat that is lost from the fire is
partially reintroduced by the incoming air.
Figure i9
The hot gases then circulate around the lower wall and around
the pot that has been placed in the outlet. Heat'is transferred
both to the pot and to the walls of the Tandoor. Depending on
the length of time that the stove has been in use, the residual
heat can be used to bake bread.
All of these stoves have the same basic components: an air and
wood inlet, an airtight combustion chamber or firebox, chimney,
heating surfaces, and adjoining flues.
Air and wood inlet --Except in some updraft stoves, wood and air
enter through the same opening. The air is controlled by a
damper at the front of the stove or at the back of the firebox
or flue. If the damper is placed at the back, wood can be fed
in continuously.
The chimney can be made from clay pipes, sheet metal, cast
iron, masonry, concrete pipes, bamboo, and so on. Brick or clay
39
pipes will have a longer life than sheet metal chimneys. The
length and diameter of a chimney are very important. The bigger
the stove, the greater should be the size of the chimney. If
the chimney is not big enough, the stove will not be able to
draw in enough air to operate at maximum efficiency. However,
if the chimney is too big, the stove may be difficult to
operate and heat losses will be increased. The maximum amount
of air that enters the stove can be altered much more
effectively by changing the diameter of the chimney than by
changing its length. It is advisable not to have a diameter
greater than 15-1/4cm (6"), as cold air could flow back down
the chimney. The height and diameter can be worked out
theoretically; however, trial and error is sufficient in most
field situations. The length of the chimney is controlled by
the height of the house; it should be higher than the highest
point of the roof.
Figure20
Figure 21
Figure 23
Figure 24
. It is not portable.
. Cracks can form around the cooking holes. Heat and smoke
will escape if these cracks are not mended regularly.
The Lorena stove's design concepts differ from both the Singer
and the HERL stoves in the following ways:
. The front damper controls not only how much oxygen is avail-
able, but where it is available and how fast it strikes the
bed of coals. This gives it a very fast response. It can be
fired up very quickly from coals, and can be damped down
more gradually. It also means that it can burn material
which is not easily combustible, such as sawdust, bark,
corncobs and, possibly, peat.
Of the three stoves discussed, the Lorena stove has found the
widest acceptance. Recent work in Nepal has shown that it uses
44
I7
and the last oven to the
chimney. The various parts are
assembled in the home. Each
joint is secured and made
airtight with mud. A baffle is
placed in the middle to help
promote heat transfer once the
ovens have been joined. The
passages connecting the first
Pot seat to the second and
third incline upward toward the
Figure25 chimney base. This improves the
stove's performance.
Figure 26
Figure 27
46
These stoves have also been widely modified for use in food
processing. Figure 28 shows a stove used by 'gula jawa' coconut
sugar producers in Blitar, East Java. It uses rice hulls for
fuel. At 3,500 Indonesian rupiahs (about $8 US), this is one of
the cheapest natural draft stoves available. Clay mortar is
used rather than cement. The l-1/2m (5') chimney draws flames
back to the last pot, l-1/4m (4-l/2') from the burning hulls in
the grate. The floor slants slightly upward toward the back of
the stove to increase the draft. The grate is a piece of per-
forated iron sheet placed almost vertically in the mouth of the
stove. There is some evidence that this type of grate is as
efficient as a step grate (Bruce Lamb, 1979). The stove will
not operate with the pots removed. When the pots are replaced,
air leaks around the edges are simply patched with a mixture of
mud and rice hull ash.
Figure 28
The pot nearest the fire is the hottest, and the one nearest
the chimney is the coolest. This is especially well suited to
the process of cooking gula jawa, as different temperatures are
required at different stages of the process. The temperatures
of the pots range from a fast to a slow boil.
Figure 29
last a long time (at least five years) and are very good con-
ductors and radiators of heat. They can be produced in a small
workshop or foundry, but are expensive to make and require con-
siderable care in their construction if they are to be air-
tight. These stoves are mainly used for heating, and must be
insulated using a refractory brick if they are to be used for
cooking only. To date only one cast iron stove has been pro-
duced specifically for Third World countries. There is no
information available on its performance or cost. Cast iron
cooking surfaces are available in the developing world, how-
ever. These stoves often have removable rings so that pots of
different sizes can be used.
Sheet steel stoves are used widely in both developed and devel-
oping countries. There are some important ways in which these
stoves can be improved-- without increasing production costs.
Wood Stoves: How to Make and Use Them, is recommended for those
wishing to improve traditional sheet steel stoves.
Ceramic
Many societies use fired clay pots as cooking vessels. The pots
are made by local craf tspeople. However, with the introduction
of steel and aluminum pots, the need for these craftspeople is
diminishing. Another source of revenue for them could be pro-
vided by the production of fired clay stoves.
. Make the clay very open. This can be achieved by adding saw-
dust, or material fibers and crushed brick, or discarded
fired pottery (grog).
2At present this is generally ascertained through trial and error. How-
ever, work is being carried out by ITDG and collaborating organizations to
develop materials that can be added to clay to improve its refractory pro-
perties. The results of this work will be published in the near future.
50
2 parts sand
3/4 part grain chaff
1 pan constarch or cassava starch
Soils with less than half clay can be used if they are already
mixtures of clay and sand rather than clay and silt. Organic
matter (leaves, twigs, straw or husks) in the soil creates
problems, so use subsoil whenever possible. The soil used is
from at least 20 to 40cm (about a foot) beneath the surface
(see Figure 32).
Figure 32
52
With too much sand the lorena is too soft and the mass will
fall apart.
With too much silt the sand/clay mix is diluted, causing inter-
ior tunnel surfaces to flake away in the heat of a cooking
fire.
Remember that although a 1:4 lorena mix (one portion soil mixed
with four portions sand) may be necessary in one place, a short
distance away a 1:2 or 1:l lorena mix may be necessary. Even
two layers of soil right next to each other may have very dif-
ferent clay contents.
Soil Sand
(Percent) (Percent) Proportion
Wet the soil until it becomes a stiff mud (thoroughly moist but
not watery). Roll the stiff mud into a pencil-thin worm of soil
about 1Ocm (4") long. The palm
of your hand can be used to roll
out the worm on a flat, hard
surface. Carefully pick up the
worm of stiff mud at one end
with just two of your fingers
(see Figure 34). Hold the worm
parallel to the ground. If the
worm breaks off, it contains a
lot of silt or sand. If it
bends or sags but does not break V
off, it contains a lot of clay., Figure 34
54
If these clay bricks are fired in a kiln, they will last much
longer. The bricks that are to be closest to the heat in the
stove should be slop-molded. This involves mixing the clay with
sawdust, 50 percent by volume. Water is added until the mixture
is very wet. The mixture is then poured into a mold. When the
brick is fired, it has a very open structure that can withstand
high temperatures. This type of brick also provides insulation
for the combustion chamber. However, these bricks are not very
strong and must either be surrounded by sturdier bricks, or
have an outer coating of lime or cement mortar.
4. HOW TO BUILD FOUR STOVES
This chapter outlines general construction procedures for four
types of wood conserving cook stoves:
All of the stoves have been built and used successfuly. Some
modification may be necessary to adapt the designs to local
conditions. Complete construction references are found in the
Bibliography.
Lorena stove
The Lorena stove (see Figure 35) was developed in Guatemala. It
resembles an improved Indian chula. It can reduce wood consump-
tion by 25 to 50 percent if used properly.
There are many reasons for this popularity. The stove can be
built by unskilled workers using local materials. Its size can
be changed for different families. Only simple hand tools are
needed. Most important, the basic technology can be adapted
broadly to different conditions and traditions.
55
56
LORENA STOVE
Figure 35
57
1. The long tunnel system extracts heat from the flue gases.
This heat would otherwise be lost up the flue.
2. The high stove mass stores heat for cooking and baking even
after the fire has died out.
3. The high mass of the firebox walls insulates the fire. This
results in higher temperatures and more complete combustion.
5. Pots fit deeply and tightly into the stove. They are
insulated from outside air. No smoke escapes.
Materials
DESIGN
The size and shape of the stove can be changed for different
families or cultures. Local traditions are very important. So
are individual household patterns. Families use their cooking
fires in different ways. Cooking pots may vary. Some cooks may
prefer to cook food quickly at high heat. Others may prefer to
cook more slowly at lower heat.
Here are some things to keep in mind during the design process:
1. Pots that need the most heat should be placed over the fire-
box. Pots needing less heat can be placed further down the
tunnel system.
3. Try to keep the hot gases under the pots for as long a time
as possible. This can be done by bending the tunnel sharply
as it passes beneath each pot (see Figure 36).
4. The cook should be able to reach the pots and damper easily.
59
-G RGJbT I
Figure 36
5. The size of the firebox should fit the amount of fuel that
is needed.
The lorena stove is made from a mixture of sand and clay (or
clay-soil). Sand forms the main mass of the stove. The clay
holds it together. Water is used to help the process.
Almost any type of sand will work. Coarse sand is best. Sand
that is very coarse or that has gravel in it should be sifted
through a screen with a 5mm (l/4") mesh. Ocean sands should be
washed to remove salt.
(
E i
Figure 37
61
Soils can also be judged by the way they feel. Clay feels
greasy. Sand feels gritty. Silt has a powdery feel. Try to
avoid silt. It offers neither structure nor bonding.
The next step is to test whether the clay can stand a firing.
Make a ball of damp clay. Place it in hot coals for an hour.
Rub its surface with your thumb after it cools. It is no good
if it flakes.
The next step is to find the best ratio of soil to sand. Test
batches made with different ratios. The ratio for soil to sand
should be between 1:l and 1:3. The ratio for pure clay to sand
should be between 1:3 and 1:s. Some clay soil will have a lot
of silt. The silt does not help the clay hold the stove
together. The clay may also have many lumps. If so, sift it
first through a 5mm screen. You can also grind it with your
feet.
It is best to mix the sand and clay when they are dry. Add
water only after the mixing is finished. The water does not
have to be clear. It can be murky. But it should not be salty.
There is a quick way to test whether the mix has the right
ratio of sand to clay. Take a handful of the mix. Add enough
water to make a patty in your hard. Press the patty slightly
against the hand. Turn your hand over, palm down, with your
fingers closed. Open your fingers slowly. The patty should fall
away cleanly. If it sticks to your hand or leaves a lot of mix
behind, there is too much clay. If it drops too quickly or
62
falls apart, there is too much sand. Adjust the ratio of sand
and clay in the mix to adjust for the test results.
Figure 33’
should be designed with toe space. This lets the cook work
closer to and more easily with the stove (see Figure 39).
Figure 39
Figure 40
64
Figure 41
Mix and lay one layer at a time onto the base (see Figure 43).
Use the tested mix. Pound the lorena in firmly with your hand,
rocks, or a piece of wood.
75
85
Figure 43
Brace the side with your hand or a board when working near the
edge (see Figure 44). Compress the edges well. These are areas
that can cause trouble.
Allow each layer to dry and firm until you cannot push your
finger in more than half the fingernail depth before adding the
next layer. It may take as long as one day per layer if the
stove is constructed indoors.
66
Figure 44
Watch each layer carefully. Add more sand to the next layer if
cracks appear. Record any changes made,
Try to keep each layer level. Work a wetted board across the top
of the completed stove in a zigzag motion. Cut away the high
parts. Fill the small holes (see Figure 45). Use the machete or
knife to even and smooth the sides.
If the lorena should crack as the pot holes and tunnels are dug,
fill the cracks with wet lorena. If cracks appear all the way
down through the stove, demolish the stove. Break the lorena up
and start again. (Cracks are due either to overworking the
lorena when the layers are applied, cutting the tunnels when the
layers are too wet, or to too much clay in the mix which causes
uneven shrinkage of the layers as they dry.)
Draw the outline of the desired layout on the stove body. Make
the outlines slightly smaller than the hole needed. Figure 37
(on page 60) shows one possible stove layout. Local conditions
may demand different designs.
67
Leveling Board
Slice small holes down the center of each pot hole and the
chimney hole. Use a spoon or knife for digging. Keep all
cutting tools wet.
Cut the damper slots with a machete or large knife. One damper
is the firebox door. The other two are located on either side
of the waterbox hole (see Figure 37 on page 60). Cut perpen-
dicularly into the stove surface, straight down into the
block. Each cut should be about lcm (l/3"). Let the water on
the blade loosen the lorena before cutting.
Let the stove dry until the stove body is very firm throughout.
Plan carefully: one hole can be made so that several pots may
be used on it (see Figure 47), Use a spoon and the pots
themselves to enlarge and shape the hole. Work carefully.
Figure 47
Begin cutting with the spoon. Then wet the sides of the pot to
be used on that hole. Twist the pot back and forth without any
downward pressure. Look at the pattern made by the movement of
the pot to see where the hole should be enlarged. Work slowly
and carefully, until the pot fits down snugly into the hole.
7. Complete Firebox
Use a machete and a pot or empty can to dig out the waterbox
hole. Dig the hole about the same height as the container you
will use for water.
9. Excavate Tunnels
Use the spoon to dig out tunnels connecting the ,firebox and the
pot holes (see Figure 48!. The tunnels must allow the hot air
inside the stove to circulate as freely as possible.
Make sure the hole for the chimney is deeper than the tunnel
inside the stove. This gives added space so that the air
passage is less likely to get clogged up with fallen debris.
70
Place a chimney pipe into the chimney hole. Sink it 15cm (6")
into the block. If the chimney needs support, put nails into
the lorena where the chimney should rest inside the stove. The
nails may not be necessary if the chi::,ney fits very tightly and
remains steady.
Add another chimney pipe. Th, higher the pipe, the better it
draws air to the stove. Loren? stoves seem to need at least
183cm (6') of chimney to operate ‘:?ficiently.
Use scrap sheet metal and make the dampers as shown in Figure
56 on page 81. Each damper should be a little wider than the
tunnel so that it can be used to control the flow of air
through the tunnel.
Rounding off the bottom edges of the dampers will allow easier
movement of the dampers inside the stove.
Smokeless ctwla
This chula (see Figure 49 on the following page) is based on
the findings of S.P. Raju and the Hyderabad Engineering
Research Laboratory. Raju's book, "Smokeless Kitchens for the
Millions," was first published in India in 1953. Since then his
chula, and variations on the basic design, have undergone
extensive testing and are in widespread use.
SMOKELESS CHULA
Pat Holes
I\ \ Platfnmj
. =rrmI,
Clw
BdY
73
Materials
. Clay --about 200 lbs.
-.
Cons true tion
Prepare four thick pieces of wood 1Ocm X 1Ocm X 60cm (4" X 4"' X
24-l/2") for the legs.
PLiTFORM
Protective
6 Tin Sheet
,
/
/
Pfeces
of Board
J 4x4x24’!+
(as needed)
Figure 50
75
Get two long boards 2-1/2cm X 15cm X 125cm (1" x 6" X 50") and
two short boards 2-1/2cm X 15cm X 75cm (1" X 6" X 30").
Nail the first two legs to the extremities of each short board.
Connect these two structures with the long boards, nailing them
well to each side. This will form the structure for the stand.
Brace table legs with diagonal boards as shown.
The clay will be easier to work with, and the finished chula
will look better, if a form is made to mold the clay. If lumber
is unavailable or expensive, the form can be eliminated.
The chula itself will be 15cm (6") high, the chimney base will
be 20cm (8") high. For the form for the chula use boards that
are 15cm (6") wide; for the chimney base use 2Ocm (8") boards.
Make the chimney before beginning the stove (see Figure 52).
Round tin cans, 15cm (6") in diameter, can be fitted one on top
of the other, or may be soldered together to form the chimney.
Prain pipes or round roofing tiles can also be used. In some
places it may prove practical to pack prepared earth around a
Pipe of suitable diameter, which is withdrawn afterwards.
Galvanized sheets, asbestos, or cement pipes can also be used.
Chimey Cap
removable for
cleaning
Tin, Clay Or
Asbestos Pipe
Chimney Figure 52
Put the form in place on the stand and draw a plan of the stove
directly on the stand. Use the dimensions in Figure 53 as a
guide.
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79
Next day, take off the water and mix the clay well with sand,
sawdust, or cow dung. Three parts of clay to one part of sand
has proved a good mixture.
Start with the base of the fire duct (channel for heat and
air), by putting down a layer of clay. The base slopes from
2.5cm (1") thick at the front to 7.5cm (3") thick at the last
pot hole (see Figure 54). Beneath the hot water chamber and at
the base of the chimney, the floor of the duct drops to 2.5cm
(1") thick again.
Build the 'walls around the duct 12.7cm (5") high. Start
building the wall to hold the chimney. Continue building up the
clay around the fire duct to a depth of 12.7cm (5"). Place a
block of clay in the center of the hot water chamber. This will
support the hot water pot without blocking the duct.
Fill the fire duct space with sand. If you are not using a
wooden form, cover the firebox opening with a piece of wood,
cardboard, or metal to keep the sand from spilling out.
Set the chimney in place. Be sure it does not slip down and
block the duct.
Put down a 2.5cm,, (1") thick layer of clay for the top of the
stove. Scrap metal strips or heavy w'ire may be used to
reinforce the stove top between and around the pot holes (see
Figure 55). Cut out the pot holes with a wet knife. Shape the
pot holes to fit the pots. This can be done by setting a wet
pot in place and gently turning it back and forth until the pot
hole conforms to the bottom of the pot. Remove the pot.
View
Section B-B
Figure 54
81
Rsinlbrce Roof
With Hard Material
(IronJile, etc.1 Figure 55
Cut 'a slot for the damper with a wet knife. Make the slot just
a little wider than the fire duct (about 1.25cm [l/2"] on
either side).
To make the damper (see Figure 56), cut a 15cm X 17.5cm (6" X
7") rectangle out of sheet metal. Nail thin wooden strips along
Wood
Thin Sh
Metal
Adjustment
Pin
Damper Figure 56
82
To use the damper, slide it into the slot. Adjust the opening
by inserting a nail through the appropriate hole. (Be careful.
The nail will get hot.)
Pans should fit the cooking holes closely. The base of the
cooking utensil should be 3-5cm (l-2") below the surface of the
hole. Be sure all pot holes are covered when the stove is in
use. Use a pot lid or a piece of metal.
Keep the stove clean. Cover all pot holes before removing ashes
from the firebox. From time to time it may be necessary to coat
the stove with a thin slurry of clay and water to clean it.
Cracks and chips can be mended with the same kind of
clay/sand/water mixture that the stove was made of.
Singer stove
The Singer stove (Figure 57) is an efficient, relatively
smokeless cooking stove similar to the smokeless chulas of
India. It can be molded in clay, or built of either sun--dried
or burned bricks. The molded stove has a life expectancy of
about a year; the sun-dried brick construction will last much
longer. A burned-brick stove is the most expensive alternative,
but will last for many years. Because the sun-dried brick
constrution is more durable without being much more costly,
directions are given here for using this material.
The stove can be built to any height and with two or more pot
holes. The stove can also be built with either a straight or
bent flue. With a straight flue, the stove requires somewhat
more room, but it is cheaper and easier to build.
Materials
. Clay
. Ashes or sand
. Sawdust, rice hulls, straw (if desired)
. Water
. Lumber and nails for 'the forms
SINGER STOVE
Cap
.
-4
Pot Holes 1
Fuel Storage
Figure 57
85
Construction
1. Make the Forms
Press the clay mixture into the form. Allow to dry slightly.
Carefully mark the cooking hole and cut it out with a wet knife
or other sharp tool. The suggested diameter of the hole is 20cm
(8"), but this may vary according to special requirements, such
as the size of the pots to be used. It will be necessary to
make two or three burner plates depending on the style of stove
you choose. The holes for the pots can all be the same size, or
can be different'sizes to accommodate a variety of pots.
Plan View
1 24 1 30 1 30
1 1 1
1 7
61 Isl 12 I
11 1
1 1 1
A form wiil also be needed for the firebox door (see Figure
59). Make it so that the finished block is 14cm X 15cm X 5cm
(5-l/2" X 6" X 2"). There should be an opening 4cm high X 6cm
wide (l-1/2" X 2-l/2") along one 15cm (6") edge. This opening
is for the damper. See the section Make the Firebox Door for
directions for finishing this block. The damper must be
attached while the clay is still damp.
Mark the outline of the base of the stove. Use the measurements
in Figure 60 as a guide. Begin to lay the bricks, using any
good mortar.
‘0
View
A-A
B-B
Mortar the cooking plates into place in the same way as for a
layer of bricks.
Rain COW
Assembling Bolt
SuppoptBrackti’
Holeo(3) Places
Equally Spaced
0
*
I FIgwe 61
i
91
Pour the clay into the special form for the firebox door. While
the clay is still damp, finish the door as follows.
With a heavy nail, punch a hole in the damper near the top
edge. Press the nail into the damp clay so that the damper com-
pletely covers the opening in the firebox door. The damper
Damper
-
Firebox Door
/’
Pivot Nail Hole
4
Bend
Damoer Layout
Damper
# Pivot Nail
\Tbo-IX2X8 Figure 62
wood strip8
92
should pivot on the nail, yet fit snugly against the clay block
to prevent the passage of air and smoke.
While the clay is still damp cut two holes halfway through the
firebox door as shown in Figure 63. 'These holes will accommo-
date the handle for the door and should be made to fit it. The
handle can be a smooth, forked, hardwood stick, or made of
coiled wire. It should be easily removed so that it will not be
in the way when the stove is in use. For a permanent handle,
make two bolt holes all the way through the door. When the clay
has dried hard, attach a wooden or bent metal handle with
bolts. (Wood will be easier to handle when hot.) Be sure the
handle is placed high enough on the blcck to clear the damper
when it is pivoted into the open position.
Firsbox Door -
c
Wooden
Handle Metal I
Handle Figure 63
93
The firebox door must fit snugly into the opening of the fire-
box. If the block is too large, it may be necessary to sand the
edges with rough sand paper. Be careful not to take too much
off.
Pans should closely fit the cooking holes. The base of the
cooking utensil should be 3cm-5cm (1" -2") below the surface of
the hole.
To clean the chimney, first cover all the pot holes. Remove the
chimney cover and sweep the chimney clean, removing all the
soot. The chimney should be cleaned at least once every six
months.
The stove is fueled by packing sawdust into the can around four
upright wooden rods (bro::lsticks are good). The sticks are
carefully removed, leaving four holes in the sawdust. A bit of
fuel oil is sprinkled on the sawdust around the holes and
lighted. When the fire is burning well, the cover is placed on
the stove and cooking can begin. Most of the smoke and fumes
will be carried away from the cooking area through the chimney.
Materials
. 1 5-gallon or 20-liter can
. Chimney cap
. Tin snips
. Soldering equipment
Construe tion
1. Make the Stove
Fasten the 1Ocm X 18cm to 8cm X 16cm (4" X 7" to 3" X 6-l/4")
reducer around the opening in the can. This can be done by
soldering or bolting.
4 4
ViTA /QENSEL- ?9
Figure 64
98
solder four equally spaced rigid metal strips between the two
pieces of duct. To the edge of the upper section attach a
flared hood that reaches down far enough to shield the opening,
but is wide enough at its lower edge to allow plenty of draft.
The flared section can be improvised by using a reducer, or can
be cut from the bottom of a chimney cap or a large funnel.
The end of the duct that fits into the stove requires its own
support, wherever the stove is used. This allows the firebox
portion to be moved easily for fueling and/or replacement.
Add a small quantity of fuel oil to each hole and light it with
a large wick. It may take some practice to learn the technique
of lighting the stove easily.
Once there is a flame in each hole, cover the can to force the
smoke and gases out of the chimney.
A 2kg (4-l/2 lb) charge of sawdust will give four or five hours
of good cooking fire.
5. HOW TO USE STOVES EFFICIENTLY
The choice and use of fuel directly affect the efficiency of a
stove. Type and condition of the wood, and the way it is placed
in the firebox all contribute to how well the stove will
operate.
Choosing wood
Some fires are more difficult to light and produce less heat
than others. The characteristics of the fuel--in this case,
wood --and how it is placed in the firebox determine the amount
of heat the fire will produce, and the rate at which heat will
be given off.
99
100
Figure 65
The denser the wood, the harder it is to ignite and the longer
it takes to burn. Dense wood also produces relatively more
coals. In the case of less
dense wood, more of the
charcoal is burned while
the gases are still burn-
ing. Thus softwood and
coconut husks produce less
charcoal and more tars, and
evolve more gases at a
lower temperature than
hardwoods. However, since
dense wood produces more
Figure 66 heat Per unit volume,
smaller fireboxes are
needed to produce the same
heat output (Figure 66').
Figure 67
logs give out considerable heat and are often used to keep a
'pot on the boil.'1
‘An ingenious and efficient method of providing energy both for heating
and cooking is the fire stick used by the Australian Aborigines. The fire
stick is a piece of hardwood 5-10~1~ (2-4”) in diameter that has been
ignited at one end. Once ignited, it is pulled away from the center of the
fire and left to smolder slowly in the sand. When camp is moved, the person
holds the fire stick in front of his body during the journey. The smolder-
ing stick gives out sufficient heat to protect the person from the freezing
desert nights but does not go into flames for two reasons:
1. the wood gases are blown away from the hot surface before they
can ignite, and
2. since the stick has a diameter greater than 2-1/2cm (l”), the
glowing end is not able to sustain its own flame.
On arrival at a new camp the smoldering end of the stick is held against
some dry grass or leaves and a new fire is started. 1
102
Basic Heat
Type of Wood Value (dry)
Tro&ical Species BTUs/lb
Using wood
A stove is being operated inefficiently when too much or too
large a piece of wood is used for a short cooking time, or when
the air inlet damper is set too low for good combustion
efficiency.
103
DC*’ Figure 66
DAMPER--A sliding door that controls the gas and air flow in a
stove.
DOWN-DRAFT--Air that flows down the chimney and into the room.
LORENA--A sand and clay mixture. (From the Spanish words lodo
[mud] and arena [sand]),
PERFORATED--Full of holes.
TOXIC--Poisonous.
109
P
110
Results of test
. on the Thai Stove, personal corres-
pondence, 1979.
Walton, J.D., Roy, A.H. and Bomar, S.H., A State of the Art
Survey of Solar Powered Irrigation Pumps, Solar Cookers
and Wood Burning Stoves for Use in Sub-Sahara Africa:
Final Technical Report, Georgia Institute of Technology,
Atlanta, Georgia USA, January 1978.
Woodstoves
Volunteers in Technical Assistance
3706 Rhode Island Avenue
Mt. Rainier, Maryland 20822 USA
Name Title
Organization
Address
Write your answers under each question. Tear out and mail the
whole page.
a) construction details
b) changes from the designs in this book
cl changes for your location
d) test results
e) other details