| Wood Burner Basics
|A Primer for the
Novice (and others).
more to the operation of a Wood
Stove-Burner-Furnace-Boiler than throwing in the Firewood and taking
out the Ashes. Whether you're starting from scratch by
ordering Steel Plate and Welding Rods, or buying a
ready-to-go unit, there are many factors to understand and consider.
These factors are not related to Wood Burner size or shape,
but generally apply
to all Wood Burners. This page assumes that Wood Burners are
with Draft controlled by the Operator.
ALWAYS WEAR SAFETY GLASSES AND
WHEN TENDING ANY WOOD BURNER.
Be sure to read our Disclaimer.
at the bottom; the Wood Burner should be sitting on a panel
of fireproof material to protect the flammable structure from the radiating heat.
Legs must be sturdy
enough to support the weight of the loaded Wood Burner (In the case of
a Boiler, this is a considerable amount), and long enough to keep it
safely above a combustible floor. VERY long Legs will bring the Wood
Burner up to a point where you may be able to
tend it without bending over, but it will also require you to lift
Firewood higher, increase the chance that it will tip over, and move it
up to where the room air is warmer which will decrease its efficiency.
The shortest Legs that support the Wood Burner safely above a
combustible Floor is common.
A word should be said here about Efficiency.
Burners are meant to heat the surrounding air. Some Wood Burners
have incorporated water tanks that heat water which is then piped to
areas where Radiators release the heat into the surrounding air.
a Boiler may be more efficient if it is well insulated, and does not
heat to escape into the surrounding air.
Efficiency is a measure of how much heat is available for the intended
use. Any heat that escapes up the Chimney or is otherwise lost
decreases Efficiency. Wood Burner Efficiency of 100% is the goal but is
not realistic. Efficiency of 80% is much more common. That means that
for every 100 pounds of wood you burn, 20 pounds is lost to
A Wood Burner in a cold room is more efficient than a Wood Burner in a
hot room. The reason is that heat is more readily transferred to the
cooler air. To demonstrate this, imagine a Glass Jar filled with 70
degree water. If we put this Jar in a Refrigerator set at 40 degrees,
within 1 hour the water will be approaching 40 degrees. If
instead, the Refrigerator is
set to 55 degrees, it may take 2 or 3 hours for the Jar to approach 55
if the Jar is put in a 70 degree room, the temperature will not drop.
the heat in the Jar does not go into the surrounding air, and its
efficiency is zero.
If Floor Flammability is a potential problem, you have the
option of replacing the floor with a Tile or other fire-safe material.
Or suspending a Steel or Sheet Metal Reflector
just below the Wood Burner to absorb the radiated heat and safely
dissipate it into the air. If the Wood
Burner is used over a concrete or Earthen floor, then this suspended
Plate will add to the efficiency of the unit by absorbing and
radiating heat into the surrounding air, which would
otherwise be absorbed by the floor.
Fire Bricks look
pretty much like regular
Bricks, except for color. But they are made especially to withstand the
temperatures inside a Firebox and protect the Wood Burner from burnout
which would make the Wood Burner unsafe. Although they reduce
the size of the Firebox somewhat, Fire Bricks are a desirable feature
found in many of the better Wood Burners on the market.
Ash can act somewhat
as Fire Bricks in cases where there are no Fire Bricks. If 3 or 4
inches of ash are left in the Firebox, it acts as an insulator and
helps to protect the Wood Burner from burnout. Approximately
1 quart of Ash is produced for every 200 pounds of Firewood
burned, depending on the species.
The Firebox Door is
where you add Firewood and
also remove Ashes on some models. It is used a LOT and must have husky
hinges and locking mechanism. A monthly application of Graphite dry
lubricant (made for Lock mechanisms) will extend Hinge
life. Some models have the Draft Control or Blower mounted on
this Door. There should be an air-tight Channel/Baffle leading to the
lowest part of the Door to prevent Sparks from shooting out and also to
minimize the escape of smoke during Chimney
down-drafts created by the wind. The Door usually has a rope-type
Gasket to seal the Door
and prevent uncontrolled Draft from giving an uncontrolled
fire. These Gaskets can be checked periodically for sealing by
the same method as a Refrigerator; a single thickness of newspaper
inserted behind the Gasket should pull out with noticeable resistance,
or tear in the attempt. A good Door will have an adjustment to make it
snug on all four sides.to prevent unwanted Draft.
A Grate is a metal grid that
suspends burning Firewood
above the Ashes, allowing Oxygen to get to the flames better than if
Firewood is surrounded by smothering Ash. Grates are usually very easy
remove, since they are a replaceable item with a lifetime of several
depending on how hard the Wood Burner is
Some Wood Burners have a Fresh Air Tube
to bring Oxygen to the Stove Pipe area. Its purpose is to burn
gases which are sometimes given off by the fire. Certain combinations
of maximum heat and minimal Draft cause gases to be formed, in the
absence of sufficient Oxygen to burn them. This tube provides heated
fresh air to allow these gases to burn and add to
the Chimney Draft.
If you ever open a Wood burner Firebox
Door and are
greeted by a "Poof", you have allowed Oxygen to enter when these gases
present. It is best to always open the Firebox Door . . . S-l-o-w-l-y.
The Draft Control is usually
located in the Ash Cleanout Door or the Firebox Door. It is a
sliding or rotating device that allows the Draft Inlet to be opened or
closed, and any adjustment in between. The more it is opened, the more
air is allowed to enter the Firebox to feed the fire, the quicker the
wood will be burned, and the quicker its heat will be
Its low location minimizes the tendency of smoke and gases from
escaping during a Down Draft, when wind blows down the Chimney with
greater force than the hot smoke trying to get up the Chimney. This
Draft opening usually has a Baffle behind it to prevent Sparks from
shooting out of the opening.
The maximum Draft opening is calculated to limit the amount of air
entering the Firebox to an amount that will not allow the fire to burn
of control. In that case the Wood Burner or its Stove Pipe might get
hot. This creates a dangerous situation which will limit the life of
Wood Burner or Stove Pipe, and may start a Chimney fire !
Draft is a simple yet
very complicated subject. It works on the principle that hot air rises.
If it did not, smoke would not
go up the Chimney, and Hot-air Balloons would not rise. Hot-air
a Propane Burner aboard which heats the air inside the Balloon to make
warmer than the air outside the Balloon.
no Draft, the fire will die; with too much, the Wood burner will
overheat. Draft is influenced by the Draft Control, by how hot the
Firebox is, the location, thickness, diameter and hight of
the Chimney, and also the Weather. When the Draft Control is
open the fire is allowed to burn hotter with minimal creation of smoke
and Creosote. It also allows a greater volume of hotter air to go up
the Chimney and keep the Chimney walls hotter instead of having a cold
Chimney cool the ascending air and decrease its tendency
underlying reason for this is that hot air weighs less than cold air.
So, like a Cork in water, it is forced up and displaced by
the heavier medium. To prove this, fasten a Balloon tightly
to a 1 liter Soda Bottle as shown here. Hold the Bottle under hot tap
water. Notice that the Balloon gets bigger. Some of the
expanding air has been forced out of the Bottle. So the air in
the Bottle is now less heavy. If the air in the Bottle weighed 2
and heating it forced half of it into the Balloon, then the half of the
remaining in the Bottle would weigh 1 ounce. So the 1 liter of
is lighter when heated. Most materials expand when heated.
A Chimney that's built inside a heated or insulated structure or on
the South side of a building will naturally be warmer than an external
Chimney on the cold, windy North side of a structure. Chimney opening
diameter also effects the temperature of the rising air. Imagine if the
opening were ten feet in diameter, there would be very little heating
of the Chimney walls by hot air from the Wood Burner. A high Chimney
will be cooler than a shorter one, and will cool the hot air on its way
to the top. Imagine a Chimney one mile high; the hot air would have no
chance of heating so tall a Chimney and
the result would be a cold Chimney that cools the hot air.
A Combustion Blower can greatly
improve the efficiency, safety, and functionality of a Wood Burner. It
can be controlled by a Thermostat that is on the wall of a
heated room, so when the room gets cool, the Blower will
quickly raise the temperature of the Wood Burner and the room. The
Blower can also be controlled by an Aquastat that is in contact with
water in a Boiler, which will quickly increase the temperature of the
water available to the associated remote Radiators.
This is especially true if your Firewood is not of uniform quality;
if you burn different species like quick, hot-burning Yellow Pine and
Slower, cooler-burning Maple with different degrees of seasoning. Then
the time required to get the Firewood burning well is much less
noticeable. Especially in the morning when you may have to get some
heat in a hurry from minimal glowing embers.
be sized to the Wood Burner and an optional adjustable inlet allows you
to fine tune the incoming air velocity for your particular conditions.
Blowers are often mounted on the Firebox Door, but they can be mounted
to the top or side with a sheet Metal channel bringing the forced air
to the Door where it helps keep the Door cool.
The Blower creates intense Flames so quickly that there is much less
Smoke created by smoldering Firewood, which equates to less Creosote.
also maintain a more even heat with less fluctuation than if the
adjusts the Draft Control to adjust the room temperature.
more constant heat can also be maintained if you are able to add
a piece of Firewood every 15 minutes or so, instead of allowing the
to die down and then adding a fresh batch which will take considerable
to catch fire and produce heat, while acting like a shield to keep the
fire from radiating heat to the Wood Burner for release into the heated
In addition, some Combustion Blowers have an automatic Draft
Control incorporated in their design. The Blower
opens a Gate which
allows air to enter from the Blower, but when the Blower is shut down
the Thermostat or Aquastat, then the Gate closes which minimizes hot
escaping up the Chimney because there is no incoming air. This design
increase the efficiency of the unit.
may be located between
the Firebox and the Stovepipe. Its purpose is to keep the hot Flames
from going straight out the Chimney. Then on its lengthened trip to the
Chimney, it will lose some heat making the Wood Burner more efficient.
can also control the Blower with a Timer or make a Set-back Thermostat
using a Timer and 2 wall Thermostats.. The Blue Thermostat is
set for night time temperature. The Red one is set for Day time
temperature. When the temperature reaches 60F. the Blue Thermostat
turns the Blower off , Unless the time is between 5 am. and 9 pm., then
the Red Thermostat will allow it to run until the temperature reaches
70F. This design is integrated into manufactured Set-back Thermostats.
The Aquastat will only allow the blower to run if the water
temperature drops below the Aquastat's setting.
A Boiler may encompass the whole
Wood Burner including
the Fire Box Door. Some Wood Burnes may even have pipes
water inside the Fire box.. This is an attempt to capture all the heat
possible which increases the efficiency factor of the Wood Burner.
These internal Pipes
need frequent cleaning to remove the Soot and Creosote which act like
A domestic Hot Water Coil may be
found In the hot water of the Boiler. It is a Heat Exchanger which
removes heat from the boiler and transfers it to the water in the
Coils. This "domestic" hot water is
then used throughout a home for bathing, laundry washing, etc.
A Circulator is used to move hot
water from the Boiler to remote Radiators to heat that remote area.
They are controlled by Thermostats in the remote area. Placement of
Circulators is normally at the lowest point of the system to prevent a
loss of water from running them dry, which can cause damage.
Shown top-mounted here for clarity only.
A Damper is a manual control
that fits inside the Stovepipe. It acts to restrict the heat going up
the Chimney. They are usually used at
night to slow the burn and preserve hot Coals for morning rekindling.
is manufactured with holes in it and clearance around its perimeter to
the Stovepipe from being closed completely, which might cause
and gases to enter the room housing the Wood Burner.
A Stovepipe Automatic Draft Regulator
automatically compensates for the varying effects of Wind and minimal
Draft. It has an adjustment to fine tune it to your particular
circumstances. On a cold Winter morning, you may notice that
it's closed. The reason is that it is not allowing air to be sucked
from the room, which would decrease the Draft. Instead, all the
draft is being pulled through the Wood Burner. But midday when a hot
is burning, the Automatic Draft Regulator will be seen merrily swinging
and down in cadence with the Wind to keep a constant Draft in your
Spark Arrestors are
usually constructed of wire mesh which impedes the travel of sparks out
of the chimney. However, unless you are able to have a hot smokeless
fire burning most of the time, then the Soot and Creosote buildup on
the wire mesh may be more of a nuisance than it's worth. Having a
chimney Sweep climb your roof to clean a Spark Arrestor
is not inexpensive; especially if it occurs on a regular basis.
Chimney Helmets will
help keep rain out of
your Chimney and Firebox . Some are made to rotate by a vane on top to
them turned away from the wind and lessen the effects of blown Rain and
sticky black residue that attaches itself to cooler surfaces. Dry
makes less Creosote than wet Firewood. It is a product of the particles
smoke; the particles which make smoke visible. A hot fire burns these
particles, but a fire which is retarded by a closed Draft Control
these tiny particles which go out the Chimney and land on nearby
as "Fly Ash". The bottom line is that a small hot fire is
a large smoldering one which produces the same amount of heat.
An accumulation of Creosote inside a Wood Burner or its
Chimney can cause problems with mechanical devices. It is also the
culprit in many Chimney fires. It is the reason why Chimney Sweeps
climb roofs with long Brushes.
An occasional hot fire may help to minimize this build up.
Down drafts are
caused by wind gusts which
are stronger than the air trying to go up the Chimney. When they
the smoke and gases are pushed back down the Chimney. If the down Draft
strong enough, it may be able to force smoke out any openings
an opened Draft Control.
Rain can cool the
Chimney decreasing the
Draft, in sufficient amounts, it can also dampen the fire itself. And
rain storms, it may be able to reach the Ashes and create a
goo that may rust holes in the Wood Stove causing its premature demise.
Repairs can be done
satisfactorily by a good Welding Shop if the Wood Burner is in
generally good condition and the damage is not too extensive. The cost
of replacement must be balanced against repair costs and state of the
art efficiencies to determine which action to take.
A weekly handful of common Table Salt thrown on a hot fire,
is said to turn Creosote into harmless dry flakes.
The bottom line is; Burn a safe HOT fire at all times,
and your Wood burning experience will be enhanced.
Always follow the Manufacturer's instructions
on every aspect of
heating your home, and if anything seems unusual,
their Dealer is as close as your