Chimney Smoke and Creosote Formation
When wood is burned slowly, it produces tar and other organic vapours, which combine with expelled mois-
ture to form creosote. The creosote vapours condense in the relatively cool chimney flue of a slow burn-
ing 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 accu-
mulated (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 generating reactions are occurring. After 30 minutes or so, the air
inlet can be turned down substantially without excessive smoke generation. Wood coals create very little
creosote-producing smoke.
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. 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. Temperatures inside
the chimney can exceed 2000°F (1093˚C). This causes much higher than normal temperatures on its exterior
surfaces. 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.
• Vibration of the chimney.
Contact your local municipal or provincial fire authority for 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.
In the event 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 the air control on the fireplace.
3. Call your local fire department. Have a fire extinguisher handy.
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 recom-
mended.
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Summary of Contents for FP25
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