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Creosote
Formation and Need for Removal
When wood is burned slowly, it produces tar and other organic
vapours, which combine with expelled moisture to form creo-
sote. 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 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.
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.
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 com-
bustion air will help to minimize the buildup.
Chimney Fires
The result of excessive creosote buildup is a chimney fire.
Chimney fires are dangerous. Chimney inside temperatures can
exceed 2000° F. This causes much higher than normal tempera-
tures in the chimney and 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
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 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.
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.
Avoiding a Chimney Fire
There are two ways to avoid chimney fires:
1. Do not let creosote build up to a point where a big chimney
fire is possible.
2. Do not have fires in the heater that may ignite chimney fires.
These are hot fires, such as when burning household trash,
cardboard, Christmas tree limbs, or even ordinary fuel
wood; (e.g.. with a full load on a hot bed of coals and with
the air inlet excessively open.)
