United States EPA-600/D-83-112
Environmental Protection Sept 1983
Agency
Research and Development
&EPA Wood Stove
Features and
Operation
Guideline for
Cleaner Air
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Are wood stoves a major pollution source?
Yes, for some pollutants, especially considering the
proximity of these emission sources to people. Many
cities such as Denver, Portland, and Missoula have
recently become concerned with this problem.
Complaints are also heard in smaller communities
across the nation.
What are the primary pollutants from wood stoves?
Carbon monoxide, organic gases, and particulate
materials including smoke, soot, and condensed organic
matter. Many people also object to the odors.
Can these emissions be prevented?
Yes, stove builders can help to reduce emissions by
improvements in design.
How can I reduce emissions from my stove?
By taking the advice in this pamphlet on:
• What stove you choose
• What fuel you burn
• How you operate the stove.
HEAT TO
HOUSE
t
BYPASS
GATE
(OPEN FOR
STARTING)
\
CATALYTIC
CONVERTER
(OPTIONAL)
HEAT
STORAGE
WALL
(NON-COMBUSTIBLE
MATERIALS)
INSULATION
Typical Wood Stove
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How to Choose a Stove
Good Stove Features
Small Size: Buy the smallest stove that will provide
enough heat. A larger stove, burning fuel at the same
rate, will have lower combustion efficiency and produce
more creosote and more air pollution.
Baffles: Properly designed internal baffle plates can
regulate the flow within the stove, ducting incompletely
burned gases through the active fire. This can provide
increased turbulence leading to more complete burning
and increased combustion efficiency. Venting the space
above the wood directly into the stove pipe may cause
high emissions of unburned organic materials, and
lower combustion efficiencies.
Ducted Air Supply: Pipes or channels that heat the
entering air and direct it within the stove into the active
flames will also increase combustion efficiency.
Firebox Insulation: Insulation, such as firebrick, around
a small fire may increase burning temperatures,
increase combustion efficiency, reduce emissions, and
store heat.
Other Design Features: Any design feature that
promotes complete burning is desired. Tests have shown
that a catalytic combustor and a heated secondary air
supply directed to the flames may be effective devices in
improving secondary combustion, and thereby reduce
emissions.
Good Installation Features
Safety: Make certain that all safety procedures and
codes are satisfied, in addition to following all the
manufacturer's directions.
Heat Storage: A large mass of noncombustible material
such as stone, brick, or water immediately adjacent to or
surrounding the stove will store heat. This device will
prolong the heat release into the house, combining
increased comfort with clean, high-rate burning in the
stove.
Supplemental Heat Recovery: For new installations, a
heat transfer device that recovers supplemental heat
from the flue pipe may permit adequate heating with a
smaller stove. This will result in a hotter, cleaner
burning fire. When such a device is added as a retrofit to
an adequately sized but inefficient stove, the burning
rate may be reduced to provide the same amount of
heat. This tends to lower burning temperatures and
increase the emission of air pollutants.
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How to Choose a Fuel
Preferred Fuels
Air Dried Hardwoods: The best combustion efficiency is
obtained when wood is thoroughly dried, for a year.
Air Dried Softwoods: These are also good fuels, but
they are slightly harder to burn cleanly due to their
higher resin content.
Properly Sized Pieces: Use kindling only for starting. For
continued burning use 4- to 6-inch-thick pieces, or
larger, depending on stove size. The larger pieces limit
the vaporization rate of the wood so that the
combustibles can be completely burned by an adequate
air supply available within the stove.
Charred Wood: This includes partially consumed fuel
remaining in the stove after the fire is extinguished. It
should be burned when the stove is relighted. It is an
ideal fuel because of its low volatile content.
Less Desirable Fuels
Freshly Cut Wood: High moisture content hinders hot,
clean burning, resulting in higher emissions of unburned
organic materials, and lower heat output.
Kiln or Oven-Dried Wood: This wood often vaporizes
too fast, resulting in emissions of organic materials.
Kindling, Cardboard, and Loose Paper: These should
be used only to start a fire. They also vaporize too fast,
leading to excessive organic emissions, and possibly to
stove overheating when burned in large quantities.
Avoid These
Household Rubbish, Garbage: These produce noxious
and corrosive products. Unburned fragments (foil, paper,
plastics, etc.) can plug gas passages, especially in stoves
with catalytic combustors.
Any Treated Wood: Rot and insect preventive chemicals
can release very toxic, even cancer-producing, materials
under the conditions within a wood stove firebox.
Synthetic logs designed only for fireplace use may be
unsatisfactory for stove use due to the binders.
Coal: Burning coal in a stove originally designed for
wood can result in the release of noxious and harmful
emissions. Coal should only be burned in a stove
specifically designed for coal. Bituminous (soft) coals are
harder to burn cleanly than anthracite (hard) coals.
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How to Operate the Stove
Stove operation at high temperatures with an adequate
air system to complete the combustion will have three
important supply benefits:
• Increased combustion efficiency
• Reduced air pollution
• Reduced creosote formation (a fire hazard).
Starting a Fire
Follow Manufacturer's Directions: First, follow the
instructions supplied with the stove. They will identify
any special techniques appropriate to your specific stove.
Starting: Kindling wood should be used only when
starting a fire. Always use larger wood pieces (4 inches
and thicker) after a bed of hot coals has been
established.
Old Wood First: Always burn first the most thoroughly
air-dried wood available. The storage of several weeks
supply of wood under a roof will prevent the burning of
wet wood, which has a tendency toward smoky burning.
Maintaining a Fire
Air Supply: Enough air must be supplied to completely
burn the gases and resins from the wood. The rate of
wood burning is related to the air supplied directly to the
wood, whereas completeness of burning requires
adequate air to be supplied to the flames leaving the
wood. After adding new wood, this requires opening the
dampers to supply air directly to the wood, and to the
flames leaving the wood.
Frequency of Adding Wood: Small frequent additions of
wood are preferred. For example, instead of adding 10
pieces at once, add 2 pieces every 15 minutes.
Prolonged Burning: After the initial high-rate burning
(about 15 minutes should char all the wood surface),
reduce the air supply over a 15-minute period if a
prolonged time of burning is desired. For overnight
operation, when a large total charge is desired, charred
wood should be accumulated within the stove over a
period of several hours, rather than firing many pieces of
wood at one time.
Watch for Signals: Visible smoke leaving the top of the
chimney or long lazy flames leaving the firebox are signs
of incomplete starved-air burning. When this occurs,
more air is needed to complete the burning. To do this,
open the dampers letting additional air into the stove,
especially air that will mix with the flames leaving the
burning wood.
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Wood Stove Air Pollutants
What are the Pollutants?
Pollution from wood stoves includes many chemical
species, the more important being carbon monoxide,
organic gases, and organic particulate matter.
Carbon Monoxide is a product of incomplete
combustion of any carbon containing fuel. It results from
the burning with insufficient air, and poor mixing, as
occurs in automobile engines.
Organic Materials consist of many different compounds
too numerous to list.
• Some of them burn completely,
• Some are changed chemically within the stove,
and
• Some leave the stove without burning.
Of the many organic materials that leave the stove,
• Some deposit in the chimney as creosote,
• Some condense and are emitted as smoke, and
• Some may condense later in the atmosphere.
The materials that have been chemically changed within
the stove include a class of chemicals called polycyclic
organic matter (POM).
Because of the seriousness of their potential effects on
people, the POMs in wood stove smoke are probably the
most significant pollutants. Some of these materials are
toxic, some are cancer-causing, and some cause
biological mutations. For example, benzo-a-pyrene, a
known carcinogen found in cigarette smoke, has also
been found in wood stove emissions. However, no
definitive studies have been conducted which correlate
wood stove emissions directly with cancer or other
specific human diseases.
Nationwide surveys of air pollution from all sources
show that wood stoves are a major contributor to the
overall pollution levels in areas of the U.S. with many
residential or commercial users of wood heating. Some
areas experience significant pollution problems related
to wood stoves, especially those with winter
atmospheric inversions and valley locations with poor air
circulation.
How to Reduce the Pollution
Specific techniques in this guide will aid stove operators
in reducing air pollution from their wood stoves. They
will also minimize the accumulation of creosote in
chimneys, and thereby help reduce the likelihood of
chimney fires.
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Comparison with Other Sources
AIR POLLUTANTS FROM RESIDENTIAL HEATING:
WOOD COMPARED TO OTHER FUELS
CARBON MONOXIDE PARTICUIATES ORGANIC CASES
All other Fuels All other fuels All other fuels
5% 46% ,2%
Emissions of these pollutants from wood stoves
represent a small fraction of the national emissions from
all sources.
From Source Assessment: Residential Combustion of
Wood, EPA 600/2-80-042b NTIS PB81-136160.
POM EMISSIONS: RESIDENTIAL WOOD BURNING
COMPARED TO ALL OTHER SOURCES IN U.S.A.
Resl.ler.tUI wood -^,,,m^,,^ , other resided!
Fuels: 1%
- Autos and trucks: 2 I %
A / \ /
All other sources: 30% •
•x. i jr
• Forest fires: 13%
These data are preliminary, and more definitive data are
needed for evaluation of their significance.
From Residential Solid Fuels, Environmental Impacts
and Solutions, Oregon Graduate Center, Beaverton,
Oregon.
Want to Learn More?
Additional information can be obtained from the
following:
Control of Emissions from Residential Wood Burning
by Combustion Modification, EPA-600/S7-81-091
NTIS PB81-217655.
Center for Environmental Research Information
Cincinnati, OH 45268.
The Woodburners Encyclopedia.
Vermont Crossroads Press, Waitsfield, VT 05673.
Wood as Home Fuel: A Source of Air Pollution.
American Council on Science and Health
47 Maple St., Summit, NJ 07901.
Wood Burning Heaters: How to Choose, Install, and
Use Them.
Tennessee Valley Authority, Solar Applications
Branch, Credit Union Bldg., Chattanooga, TN 37401.
Proceedings: Residential Wood and Coal Combustion
Specialty Conference, March 1982.
Air Pollution Control Association, P. O. Box 2861,
Pittsburgh, PA 15213
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