Chimney fires occur when the combustible deposits on the inside of a chimney burn. The deposits may
be ‘raw’ creosote, pyrolyzed creosote, or soot. Ignition requires adequate oxygen, which is usually
available, and sufficiently high temperatures the same conditions as for the ignition and combustion of
any fuel. Chimney fires are most likely to occur during a very hot fire, as when cardboard or Christmas
tree branches are burned, or even when a stove burns normal wood, but at a higher than normal rate. A
cracking sound can often be heard at the beginning of a chimney fire. As the intensity of the fire rises, the
stovepipe will sometimes shake violently, air will be very forcefully drawn in through the stove, and the
stovepipe may glow red hot. A tall plume of flame and sparks can be seen rising from the top of
uncapped chimneys.
The most effective way to suppress a chimney fire is to limit its air supply although both water and salt are
sometimes suggested. If a relatively airtight stove is the connected appliance. This is easily done by
closing the stove’s air-inlet dampers, if all the stovepipe and or chimney joints are tight, and no other
appliance is connected to the same flue.
In a properly designed and maintained chimney, the only potential hazard related to chimney fires is
ignition of the building’s roof or top of the chimney. A spark-arresting screen can decrease, but not
eliminate this possibility, but spark screens themselves are often clogged. The chimney itself and the
stovepipe, when properly installed, are intended to withstand an occasional chimney fire without danger
of ignition of their surroundings. During a chimney fire, one ought to check the roof and surroundings,
and possible wet down critical areas. I f the chimney may not be up to safety standards, one should also
keep a close watch on all surfaces near the chimney.
Some people start chimney fires fairly frequently, as a means of chimney cleaning. This defers very
intense chimney fires and the small ones, which do happen, are always under a watchful eye. Under
some circumstances, this practice may be reasonable, but generally it is a risky method to keep the
chimney clean. There is always danger of a house fire, but in addition, any chimney fire is wearing on a
chimney; the high temperatures increase the corrosion rate of metals and the thermal expansion of
masonry materials encourage crack formation and growth.
Chemical chimney cleaners are available. Opinions on their effectiveness vary, but apparently when
used regularly, and as directed, they work, and do not damage chimneys. The usual chimney cleaning
method is the oldest human energy and some kind of mechanical tool. A stiff wire brush, a heavy chain
(perhaps in a bag) hung with a rope and worked up and down from the top of the chimney, and very small
brushes have all been used. Professional chimney sweeps are also reappearing.
Some people clean yearly, other after every few cords of wood burned, but there are so many factors
influencing creosote build up that such generalizations are not appropriate in most particular cases. In
new installations, or when changes occur (such as a different stove) the chimney should be checked
frequently (after 2 weeks, than after a month, then after another 2 months, etc.) until it is clear how
frequently cleaning is usually needed
The preceding is an excerpt from “THE WOODBURNERS ENCYCLOPEDIA” published by Vermont
Crossroads Press, Inc. – Dec., 1976.
To Next Page
Loading...
