HOW TO BUILD AN ENERGY EFFICIENT CLAY OVEN AND CLAY STOVE

HOW TO BUILD AN ENERGY
EFFICIENT CLAY OVEN AND
CLAY STOVE
Background and Motivation. (Global Warming and Climate Change)
Every time you use electricity, ESKOM needs to burn coal to generate more electricity for you.
Through the process of generating electricity Carbon Dioxide (CO2) is released into the
atmosphere. CO2 is one of the major greenhouse gases contributing to Global warming and
Climate change.
Did you know?



For every Kwh of electricity generated, 0.98 KG of CO2 is emitted into the atmosphere.
For every liter of petrol combusted, 2,4KG CO2 is emitted
For every Kg of LPG gas burned 0,3KG CO2 is emitted into the atmosphere.
Furthermore, the burning of coal causes poisonous gases to be released into the environment
and Witbank where South Africa’s coal mines and power stations are located has been reported
as having one of the worst air quality in the world.
“Some of the highest levels of poisonous gases in the air
are found above Witbank, in Mpumalanga, and the
surrounds. The levels of chromium and barium were so
high that a European Union research team’s instruments
had been unable to take accurate measurements, Beeld
reported today…. They said the levels of heavy metals in
the air above the team’s research area were, according
to their information, the highest in the world.” (25 April,
2013)
There is a desperate need for us to mitigate our impacts on the environment and to change our
behaviors and attitudes so that we can live sustainably. All over the world people are seriously
looking at ways to cut down carbon emissions. In South Africa reducing electricity (and hence
coal burning) is one way this can be done.
Building a clay oven and clay stove that use a very small amount of wood instead of an electric
stove/oven, is a way to cut down on carbon emissions.
This simple technology is extremely energy efficient, using very little wood and if you use
sustainably harvested timber your impact on the environment is minimal. This is because you
are burning current carbon and not using fossil fuels which are ancient sources are carbon.
Clay ovens and traditional clay stoves have been used for hundreds of years worldwide to cook
food. There are even stories of people digging holes in termite mounds to bake bread. People
also used to dig a simple hole in the ground in which they placed hot coals and then their pot
after which they covered up the hole.
How does it work?
The basic idea behind a Clay oven is that you burn
wood to heat the oven's Clay and after about one and
a half hours, remove the coals. The heat of the fire has
been absorbed by the floor and walls of the oven, and
this heat will now cook your food. The cooking heat
comes in all three forms: conduction from the floor
and air to the food, radiant from the walls to the food,
and convection due to the uneven heating of the walls
causing the air inside to swirl. Once the oven is hot,
the oven can maintain heat for many hours, depending
on the mass (thickness) of the walls and floor.
The principle behind the clay stove is that a small fire
is made on the floor and the potjie pot placed on the
fire. Because the space between the pot and the walls
of the stove is so small all the heat from the fire is
forced up around the pot heating it and the walls of
the stove as it moves up. No heat is wasted. The heat
that is not absorbed by the pot itself is held in the
walls of the stove and then passed back to the pot.
You can cook for 3hrs with one and a half kg or less of wood. Their energy efficiency makes the
clay oven and stove attractive alternative ways of preparing food.
An added bonus is that it is widely known that food prepared using fire wood is far tastier than the
taste of a conventional stove or oven.
What do you need?
1. Clay. (A redundant termite mound makes excellent clay.) About 10 x 25 kg bags of clay soil
will be sufficient. If you don’t have termite mounds you can use any clay soil or clay from a
river. You will need to add dry grass to this to provide extra strength)
2. A spade
3. Water
4. Newspaper
5. A large piece of plastic such as a garbage bag
6. Door and handle. Ply board and metal sheeting works well. Toilet roll holders make for
cheap handles.
7. 6 x40mm long screws, 6x 10mm long screws (drill bit the same size as the screws, saw, tin
snips, screw driver and drill.
Before you begin you need to decide how large an oven you want to build. You can do this by
deciding on the number of bread pans you would like to place in the oven or by looking at any
cooking containers you will want to use. After doing this you can judge the size for the foundation.
The clay oven shown in this resource can fit 3 medium size bread pans and the door opening can
accommodate a baking tray should you wish to make pizza.
Building the Oven – There are four stages
1. The Foundation
The foundation should be a minimum of 15cm thick.
Make the base wider than the dome you will build
to ensure maximum heat absorption.
2. The Hearth “the part on which the dome of the oven rest”
Mixing the Clay
Make sure all stones are removed and add water to the clay
soil and start to mix it. It’s easier if you take your shoes off
and stamp it with your feet. You can also pack stones in with
the clay while you make the hearth. Make sure your clay
becomes stiff enough to make a sausage. If the clay is too
wet you will not be able to build the dome. It will simply run
down to the ground.
Laying the Hearth
You can also pack stones in with the clay while you make the
hearth. Make sure you stamp the clay firmly and make the
layer as flat as possible.
3.
The Door
This door is made with 20mm ply board. Two 39cm x 47cm
rectangles are cut and the top edges rounded of. The two
parts are screwed together.
A piece of flat metal sheeting is cut to the same size and
screwed to the door. A pair of tin snips works well to cut the
metal sheeting. The metal sheeting protects the wooden
door from burning and reflects heat in the oven. Handles
need to be screwed on and for these toilet roll holders work
well or anything you can get a grip on.
4. Clay dome
This is the part where the inside of the oven is shaped.
Lay some wet newspaper over the hearth and use sand to
build a dome.
Once you have your desired sized dome, push the door,
which you have covered with plastic, against the sand
dome. If you don’t cover the door the clay will stick to it
and you won’t get it out.
Cover the sand dome with wet newspaper as it helps to
make the clay stick.
Pack clay on the sand dome. Start from the bottom and
work up. A layer of about 15cm thick will make for a very
well insulated oven. The clay will crack as it dries, so be sure
to fill in the cracks. When you fill in the cracks, lightly wet
the area around the crack as it will help make the clay stick.
Note: very runny clay is called “slip”
As soon as the clay has stopped cracking it’s nearly ready
for use.
Carefully remove the door and start to scoop out the sand.
TIP: You can paint stone sealer on your oven to protect it
from the elements if you don’t want to build a shelter for it.
Using the oven
When you make your first fire in the oven, the clay will
become vitrified (baked) and very hard.
Make a decent sized fire and let the coals heat the clay for
up to an hour and a half after which remove most of the
coals. Place the coals nearby in case your oven is not hot
enough so that you can add more coals if necessary.
When you feel that the temperature is right, put in the
bread and close the door.
TIP: After 5 minutes check on the bread to make sure it’s
not burning.
Your bread will be ready to eat in around 45 minutes.
The clay oven is very versatile. You can cook roasts, make
pizza and bake just about anything.
For more designs, please visit:
http://www.How to build a simple wood fired cob
oven.mht
http://www.squidoo.com/building-an-earth-oven-cob-oven
How to build a Traditional Fuel Efficient Clay Stove
Advantages.
You can cook for 3hrs with only 1,5kg of wood. You can use small
twigs to cook the whole meal. This can save electricity and
money.
What you need!




Three medium sized stones and a 3 legged pot
Five volumes (buckets) of clay. Old termite mounds work well for this
One volume of dry grass
Water
Preparing the clay mixture
Mix the clay and water and add the dry grass. Mix well till the clay can be rolled into a sausage or
ball.
Construction
Step 1
Choose a place for the stove, making sure the entrance for the wood is
facing the direction of the wind. Place the stones in a triangle, making
sure the sides of the triangle are equal in size. Also make sure the pot fits
between the stones.
Step 2
Fix the stones in the ground in small holes. Put some clay mixture around
them
Step 3
Control the distance between the floor and the pot by putting a few
sticks of wood underneath. The distance should be about 12 to 14cm.
Step 4
Take out the wood and start laying down coil after coil of the clay mixture
in a circle, joining the three stones. Make the lower part of the clay wall
thicker than the upper part.
Step 5
Wet the pot and place it on the three stones. Start laying clay around the
pot until you reach the top. Pack the clay slightly away from the pot to
leave a gap.
Step 6.
Remove the pot while turning it slowly to widen the gap (about the width
of your fingers). This is necessary to ensure airflow for the fire.
Step 7
Mark out the entrance of the stove, making it round on the top and
shaping a little platform for the wood in front of the entrance. Smooth
out the edges of the entrance and the surface of the stove. Allow the
stove to dry.
It will crack during this process, so keep filling in the cracks until it stops.
When the stove is dry you can use it. Make sure not to put too much wood inside and not to sit in
front of the entrance. The air needs to get to the fire.
After cooking, put out the fire in order not to waste wood. During the rainy season, cover the
stove to protect it against rain.
TIP: Paint stone sealer on the stove to protect it from the rain