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Chimney Smoke and Creosote Formation
When wood is burned slowly, it produces tar and other organic vapours, which combine with expelled moisture to form
creosote. The creosote vapours condense in the relatively cool chimney flue of a slow burning fire. As a result, creosote
residue accumulates on the flue lining. When ignited, this creosote makes an extremely hot fire. The chimney connector
and chimney should be inspected periodically (at least once every two months) during the heating season to determine if
a creosote buildup has occurred. If creosote has accumulated (3 mm. or more), it should be removed to reduce the risk
of a chimney fire.
1. Highest smoke densities and emissions occur when a large amount of wood is added to a bed of hot coals and the
air inlet is closed. The heated wood generates smoke, but without ample air, the smoke cannot burn. Smoke-free,
clean burning requires small fuel loads, two or three logs at a time or 1/4 to 1/2 of fuel load and leaving the air inlet
relatively wide open, especially during the first 10 to 30 minutes after each loading, when most of the smoke gener-
ating reactions are occurring. After 30 minutes or so, the air inlet can be turned down substantially without exces-
sive smoke generation. Wood coals create very little creosote-producing smoke.
2. The cooler the surface over which the wood smoke is passing, the more creosote will be condensed. Wet or green
wood contributes significantly to creosote formation as the excess moisture that is boiled off cools the fire, making
it difficult for the tars and gases to ignite, thus creating dense smoke and poor combustion. This moisture-laden
smoke cools the chimney, compounding the problem by offering the smoke the ideal place to condense.
3. In summary, a certain amount of creosote is inevitable and must be lived with. Regular inspection and cleaning is the
solution. The use of dry, seasoned wood and ample combustion air will help to minimize annoying smoke emissions
and creosote buildup.
Chimney Fires
The result of excessive creosote buildup is a chimney fire. Chimney fires are dangerous. Chimney inside temperatures
can exceed 2000° F(1100°C). This causes much higher than normal temperatures in the chimney and on its exterior sur-
faces. Thus ignition of nearby or touching combustible material is more likely during a chimney fire. Proper clearances
are critical during such a fire.
Chimney fires are easy to detect; they usually involve one or more of the following:
•
Flames and sparks shooting out of the top of the chimney
•
A roaring sound and/or a vibration of the chimney
In Case of a Chimney Fire
1. Prepare to evacuate to ensure everyone's safety. Have a well understood plan of action for evacuation. Have a place
outside where everyone is to meet.
2. Close air inlet on stove.
3. Call local fire department. Have a fire extinguisher handy. Contact your local municipal or provincial fire authority or
further information on how to handle a chimney fire. It is most important that you have a clearly understood plan on
how to handle a chimney fire.
4. After the chimney fire is out, the chimney must be cleaned and checked for stress and cracks before starting another
fire. Also check combustibles around the chimney and the roof.
•
The services of a competent or certified installer, (certified by the Wood Energy Technical Training program (WETT) -
in Canada, Hearth Education Foundation (HEARTH) - in U.S.A.,) are strongly recommended.
5055.7298-A
Safety
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