B 1, 3
D 1, 3
Forms of energy
Among oldtimers, stove building was an art form. There were different
kinds of stoves for different applications: tent stoves, steambath
stoves, and stoves for larger and smaller cabins. People developed
precise skills in cutting and shaping iron. Many experiments took
place and stove construction was a common topic of conversation.
I have spent a lot of time thinking about and making better stoves.
The ultimate stove always seems to be the next one I build.
One time a young girl came into our cabin. I had a stovepipe standing
on the floor. She circled it carefully, studying it. She had seen
me experiment with so many crazy things she couldnt believe
that it was just an ordinary stovepipe standing on the floor. She
thought it was another of my wild ideas. I have filled houses with
smoke, but have never burned one down.
My study of stoves has given me insight into the ways other things
work as well.
is a process of nature by which wood is developed.
water + carbon dioxide + suns energy (light) + minerals
This process takes many years. When we bring a tree home, we are
bringing energy stored in the wood from years of the suns
radiant energy. The light energy of the sun has been converted to
chemical energy in the wood by photosynthesis.
Releasing the Energy
When we apply heat to wood in the form of a match and a little
burning paper, we start the process by which the chemicals in the
wood release their energy. This process is the opposite of the process
by which the tree grows.
The stored chemical energy of the wood is changed to heat energy.
We use that energy to heat our homes.
Wood + Oxygen = Water + Carbon Dioxide + energy (heat) + minerals
When we heat our homes with wood, we are releasing the stored
energy of the sun from years past. We receive energy from a time
before many of us were born. That is amazing. Energy stored for
twenty, thirty, sixty, or eighty years is released in four to five
The smoke from a wood fire contains water, carbon dioxide, carbon
monoxide, minerals, and some heat energy. The ashes left in the
stove represent the minerals left behind.
Starting a Fire
things are necessary to have fire:
If we try to start a fire by applying a match to a log, it wont
burn. The match cant provide enough heat to get the log burning.
We have enough fuel and enough oxygen, but not enough heat.
If we start a fire with small pieces (shavings and kindling),
not much heat is required to get them burning. There is a great
amount of surface area that can burn, and not much wood to heat
to the kindling temperature. There is sufficient fuel, heat and
Once we get the smaller pieces of wood ignited, they provide enough
heat to get the larger pieces burning.
Birch bark is an excellent firestarter, but the supply is quickly
exhausted close to a cabin. Some people use dry grass. Shavings
and kindling are prepared in the evening so a fire can be readily
made in the cold morning.
If we want to speed up the burning process, we can increase any
one or all three: fuel, heat, oxygen.
Adding wood to a fire increases the amount of heat because more
fuel is available to burn.
Increasing Air (oxygen)
Increasing the amount of air (oxygen), makes a fire burn faster.
This is why we blow on a camp fire or fan it when it is reluctant
We can do this by insulating the stove with bricks as we do in
modern wood stoves, or moving the pieces of wood closer together.
slower than little ones
Controlling a Fire
Wood stove. We control a wood stove by controlling the
amount of air allowed into the firebox and controlling the amount
and type of wood.
Campfire. We control a campfire by spreading the wood apart
or bringing it together. We add wood gradually to give a sustained
There are two ways to control the air supply in a wood stove:
- At the stove door
- With the damper
most important feature is an air intake control that doesnt
leak air into the fire when it is shut down.
If we close the damper on the stovepipe, the fire slows down.
Fire needs oxygen to continue.
The air intake is slowed down by the control in the front of the
stove. The air exhaust is slowed down by the damper.
Controlling Fuel Available
We control the fire by the amount, type, and size of fuel we put
in. A stove filled with wood will burn harder than a stove one-quarter
Dry wood burns faster than green wood.
A solid block of wood burns slower than the same block of wood
split into many pieces. Wood can only burn on its surface.
If we increase the surface area of wood by splitting, it burns much
Placing the Wood
Before going to bed at night, I put two big logs on the outside
of the stove and put the smaller pieces in the middle. The smaller
pieces burn out during the night. The big logs are far apart in
the stove causing them to burn much slower than if they were close
together. Their charred remains are all thats necessary to
start the mornings fire.
Mud and Bricks
Dirt in the bottom of the stove acts as an insulator, keeping
the stove from getting too hot on the bottom, endangering the floor.
Dirt also retains heat in the stove, keeping the temperature and
rate of burning even. It takes a while to warm the dirt, but once
it is warm, the retained heat helps keep the fire going. In the
morning, a few burning embers on the dirt base make fire starting
an easy task.
Oldtimers avoided putting black rocks in the stove as their water
content causes them to explode. Their internal water turns into
steam and expands violently. When setting a tent stove in the winter,
there is sometimes no choice but to get gravel from the bottom of
the waterhole in the creek or river. All other dirt is frozen. The
first night is often lively.
Today, most manufactured stoves are lined with bricks that hold
heat, keeping the temperature in the firebox steady.
air rises because it is thinner and lighter than cold air. Wood
stoves draw air into the firebox and, as the air is heated in the
fire, it naturally rises up the stovepipe. Modern stoves and stovepipes
allow heat into the home while directing the smoke outside.
In traditional Alaskan housing, the smoke rose and exited the
house through a hole in the roof.
can't hold enough wood
Considerations in Design
If a stove is too big, the fire is too far from the stoves
surface. It wont throw much heat. Years ago I saw a 100-gallon
drum converted to a stove. It consumed huge quantities of wood,
and threw little heat. A 55 gallon drum is just right to make a
stove for a house.
If the stove is too small, it cant hold enough wood to burn
for long. Small stoves also require splitting the wood very small.
If a stoves top surface isnt flat, it is dangerous
trying to heat water or cook on it. If the surface is too high above
the fire, it will take a long time to boil water. If the surface
is too low, the stove cannot hold enough wood.
If the surface is black, it will radiate heat well. A light colored
stove will not radiate heat well at all.
the stovepipe is too large in diameter, it will draw all the hot
air up the pipe, and wont throw much heat into the house.
If the stovepipe is too small in diameter, the fire cant get
enough air to burn well.
If the stovepipe is too short, it cant get enough upward
draft and will burn poorly. When the wind comes from the opposite
side of the house, there is an eddy effect off the roof. The wind
blows down the stovepipe and blows smoke into the house. The teachers
quarters in my second village did this. Several times we ran out
of the house with tears pouring down our cheeks.
The most dangerous place for highly flammable creosote and soot
to accumulate is where the pipe emerges from the building. The smoke
is condensed there because the pipe is cooled greatly at that point.
This is also where the pipe is closest to the building materials.
When a fire occurs in a stovepipe, it is called a stack fire.
Stack fires have burned many Alaskan homes to the ground. Nowadays
we use insulated metalbestos pipes. Before metalbestos, we had only
black or galvanized pipes, and homemade roof jacks.
If the stove cant control the air flow well, the fire will
rage for a while making the house too hot, then it will go out long
before morning. If the stove is too airtight the stovepipe will
soot up dangerously within a few weeks.
Modern technology has brought us wire brushes to clean our stovepipes.
From the roof, we used to rattle a dog chain tied to a small rope
up and down inside the stovepipe.
A tent stove must be light for transport. We used to make stoves
out of square five gallon cans. We cut the tops off and put two
of them end to end.
A stovepipe damper makes a big difference in controlling the fire
in a camp stove. Lacking a commercial damper, we used to slit the
stovepipe crosswise with a hacksaw and used a piece of thin metal
to slide in an out of the slot as a damper.
Four inch stovepipe is the best for this kind of stove.
This kind of stove is good for a tent if weight of transport isnt
a big problem. It is also good for a small cabin.
The top is flat, and it boils water and cooks food well. A five
inch stovepipe is best for this kind of stove. The best height,
according to the oldtimers, is 14 from bottom to top (not
rim to rim). Three light-colored rocks in tripod fashion make good
This stove is better for houses and larger steambaths. A good
airtight door is a must for a home. Such stoves hold large quantities
of wood, but can they get very hot if the air is not controlled.
Commercial doors made from cast iron are best, as the amount of
heat generated will warp most homemade doors.
This type of stove uses a six-inch stovepipe.
Modern Commercial Stoves
There are a multitude of commercial stoves available today. For
a while they made sense, having fans to increase heat transfer,
thermostatically controlled air flow, airtight doors, preheated
intake air, and even catalytic converters. Nowadays many are so
filled with pollution controlling devices you cant get enough
wood in them to heat the house. Some of the features of newer stoves
are as follows.
Thermostatically controlled airflow. Two kinds of metal
are bonded together and wound in a spiral. The two metals expand
at different rates when heated. It is called a bimetal helix
coil. It requires no electricity to operate. It is connected
to the air intake door. When it is cooled, the coil contracts, pulling
the air intake door open to the stove. When it is warmed, it expands,
allowing the air intake door to fall shut.
Airtight Doors. If the door isnt airtight, air can
leak into the fire, and it will roar until the wood is consumed.
Doors used to be sealed with asbestos. The new man-made material
tends to shrink and fall out after a while, requiring replacement.
Modern stove doors dont compare with the ones that used to
Preheated Air. If cold air is drawn into the firebox, it
slows down the burning of the fuel. Remember, heat is one of the
necessary ingredients of burning. Burning is more efficient when
the air being introduced into the firebox is warmed first.
Catalytic Converters. The idea is wonderful. When a stoves
air supply is shut down, many gasses are given off from the wood
that have tremendous energy potential. They used to be lost up the
stovepipe. On the surface of a catalytic converter, in the presence
of fresh preheated air, the gasses are burned efficiently . . .
In reality, there are problems. The catalytic converters become
plugged and soot up. They are damaged when printers ink or
other chemicals are burned in the stove. Often people bypass the
catalytic converter or take them out because they function poorly
after several months.
When we burn oil in a stove, we
- allow the stove to have all the air it needs, and
- control the amount of fuel.
When we burn wood in a stove, we:
- put a large amount of fuel in the stove, and
- control the fire by restricting the air.
In an airtight woodstove, this produces incomplete burning. If
a stove is not airtight, the fire is seldom at the desired temperature.
If we could leak the wood gradually into the firebox
and allow free airflow in the manner of an oil stove, burning would
be more efficient.
In the front of the log, burning is fairly complete. There is
fuel, oxygen, and enough heat. However, when the mixture of smoky
gasses go to the back of the log, the air has been exhausted of
its oxygen. Many gasses are released from the back of the
wood that dont have the opportunity to burn and release their
heat. Long logs dont burn as efficiently as shorter ones for
When wood is green or the water content is high, there
are additional problems. Water boils at 212°F. Wood kindles
at about 460°F. Before the wood can burn, the water must be
boiled out of the wood. It takes plenty of heat to boil water. So,
about 20% of the heat that should be going to our home is going
to boil the water out of the wood. Robbery!
Further inefficiency: when the water is boiled away as steam,
the steam screens much of the oxygen from contacting the flame.
Green wood has the same potential energy as dry wood, but too
much of that energy is used up boiling the water away. This is why
many people split wood and let it season for a year or two before
burning it. They allow the sun to dry the wood for them. I heard
of people falling birch trees in the fall while the leaves are still
on the tree and cutting them into pieces several months later. The
leaves provide a great surface area to wick-dry the tree. I tried
this once. It works well in theory, but it was too hard to maneuver
through all the branches with eight to ten trees all tangled together.
- To demonstrate that water is a byproduct of combustion, hold
a very cold piece of metal over a small flame. Can you get the
water in the smoke to condense on the plate?
- Hold your hand a safe distance over a candle flame. Can you
feel the warm air rising. Can you devise a way to demonstrate
this to others, like a pinwheel? (My last pinwheel burst into
- Look at the wood stoves in your village. (Does everyone burn
oil? Check the steambaths.) Note the controls for air intake.
How many different kinds are there? Are most of the doors airtight?
What kind of dampers do the stoves have? Do all the stoves have
either mud or bricks inside?
- Find a wood stove with a bimetal helix coil. Heat it with a
blow drier or other safe heat source. Watch it close. Cool it
with a fan or cold water. Watch it open. Gently file both sides
of the coil. Which is harder? Can you guess what kind of metals
- Put a very green stick of wood on a burning fire (a block from
the top of the tree will illustrate well). After ten to fifteen
minutes, open the stove door and observe the steam coming from
the wood. Can you hear it hiss?
- Get an old stovepipe that has been used on a wood stove. Scrape
the inside. What does the material smell like? Put the material
you have scraped on a metal plate and heat it. What happens. Try
to burn the material. Does it burn? Was the stove losing heat
by not completely burning the wood?
- Make a campfire. Fan the flame. Does this increase burning?
If so, why? Put more wood on the fire. Does the fire burn stronger?
Why? Pour water on the fire. What happens and why?
- Put a candle in a jar. Light it. Put a metal cover on the jar.
What happens and why?
- Discuss the difference between the convenience of burning green
wood versus the efficiency of burning dry wood. Ask the oldtimers
in the village about the advantages of each.
- Send for information on modern commercial wood stoves. Discuss
the advantages of the different features.
- Talk to some of the oldtimers in your village about stoves
they used to use for travel, for cabins, and homes. Is the information
consistent in your area with what I have presented here? If there
are differences, why do you think they exist?
- What things go together to make wood?
- When your house or tent is heated by a wood fire, where did
the energy originally come from?
- What three things does it take to make a fire?
- What happens if a fire doesnt get enough air?
- With a given amount of air, how can you cause wood to burn
- What does mud in the bottom of the stove do, or firebricks
in the modern stoves?
- Comment about the size of a stove, surface, size of stovepipe,
and air intake.
- In an oil stove we control the flow of fuel. In a wood stove
we control the flow of what?
- What are the disadvantages of burning green wood?
- How many cubic feet are in a cord of wood? (4 x 4
- How many cords are in a pile 8 x 5 x 13?
- If green wood has 2/3 the available heat as dry wood, and dry
wood is $125 a cord, what is the fair price for green wood if
the same value is to be obtained?
- What is the area of four stovepipes, 4, 5, 6
and 8. Is the area of the 4 pipe 2/3 the area of the
6 pipe? (When pi is 3.14)
- Look at a block of wood. Measure the diameter from the ages
of fifteen and sixteen years. Be kind to yourself; use metric
measurement. If the block were a perfect circle, what is the area
for each year? How much did it increase in one year? Do the same
operation between thirty-three and thirty-four years. How much
did it increase? How much greater or less was the growth in area
of the tree when it was younger than when it was older? Figure
the difference in volume if the block is .5 meters long.
- Compute the volume of the inside of three local stoves. Compute
the area of the stovepipe of each stove. Is there a relationship
(bigger stoves have bigger pipes)?