As you snuggle in front of a
cozy fire or bask in the warmth of your wood stove, you are taking
part in a ritual of comfort and enjoyment handed down through the
centuries. The last thing you are likely to be thinking about is the
condition of your chimney. However, if you don't give some thought
to it before you light those winter fires, your enjoyment may be
very short-lived. Why? Dirty chimneys can cause chimney fires, which
damage structures, destroy homes and injure or kill people.
Chimney fires can burn
explosively - noisy and dramatic enough to be detected by neighbors
or passersby. Flames or dense smoke may shoot from the top of the
chimney. Homeowners report being startled by a low rumbling sound
that reminds them of a freight train or a low flying air plane.
However, those are only the chimney fires you know about.
Slow-burning chimney fires don't get enough air or have enough fuel
to be as dramatic or visible. But, the temperatures they reach are
very high and can cause as much damage to the chimney structure -
and nearby combustible parts of the house - as their more
spectacular cousins. With proper chimney system care, chimney fires
are entirely preventable.
CREOSOTE & CHIMNEY
FIRES : WHAT YOU MUST KNOW
wood stoves are designed to safely contain wood-fueled fires, while
providing heat for a home. The chimneys that serve them have the job
of expelling the by-products of combustion - the substances given
off when wood burns.
As these substances exit the
fireplace or wood stove, and flow up into the relatively cooler
chimney, condensation occurs. The resulting residue that sticks to
the inner walls of the chimney is called creosote. Creosote is black
or brown in appearance. It can be crusty and flaky ... tar-like,
drippy and sticky ... or shiny and hardened. Often, all forms will
occur in one chimney system.
Whatever form it takes,
creosote is highly combustible. If it builds up in sufficient
quantities - and catches fire inside the chimney flue- the result
will be a chimney fire. Although any amount of creosote can burn,
sweeps are concerned when creosote builds up in sufficient
quantities to sustain a long, hot, destructive chimney fire.
Certain conditions encourage
the buildup of creosote, restricted air supply, unseasoned wood and
cooler-than-normal chimney temperatures are all factors that can
accelerate the buildup of creosote on chimney flue walls.
Air supply : The air supply
on fireplaces may be restricted by closed glass doors or by failure
to open the damper wide enough to move heated smoke up the chimney
rapidly (the longer the smoke's "residence time" in the flue, the
more likely is it that creosote will form). A wood stove's air
supply can be limited by closing down the stove damper or air inlets
too soon and too much, and by improperly using the stovepipe damper
to restrict air movement.
Burning unseasoned firewood :
Because so much energy is used initially just to drive off the water
trapped in the cells of the logs - burning green wood keeps the
resulting smoke cooler, as it moves through the system, than if
dried, seasoned wood is used.
Cool flue temperatures : In
the case of wood stoves, fully-packed loads of wood (that give large
cool fires and eight or 10 hour burn times) contribute to creosote
buildup. Condensation of the unburned by-products of combustion also
occurs more rapidly in an exterior chimney, for example, than in a
chimney that runs through the center of a house and exposes only the
upper reaches of the flue to the elements.
HOW CHIMNEY FIRES
Masonry chimneys. When
chimney fires occur in masonry chimneys - whether the flues are an
older, unlined type or are tile lined to meet current safety codes -
the high temperatures at which they burn (around 2000' F) can "melt"
mortar, crack tiles, cause liners to collapse and damage the outer
masonry material. Most often, tiles crack and mortar is displaced,
which provides a pathway for flames to reach the combustible wood
frame of the house. One chimney fire may not harm a home. A second
can burn it down. Enough heat can also conduct through a perfectly
sound chimney to ignite nearby combustibles.
factory-built, metal chimneys. To be installed in most
jurisdictions in the United States, factory-built, metal chimneys
that are designed to vent wood burning stoves or pre- fabricated
metal fireplaces must pass special tests determined by Underwriter's
Laboratories (U.L.). Under chimney fire conditions, damage to these
systems still may occur, usually in the form of buckled or warped
seams and joints on the inner liner. When pre-fabricated,
factory-built metal chimneys are damaged by a chimney fire, they
should no longer be used and must be replaced.
WAYS TO KEEP THE FIRE
YOU WANT... from Starting One You Don't!
Chimney fires don't have to
happen. Here are some ways to avoid them :
If you think a chimney fire has
occurred, call a Professional Chimney Sweep for a professional
evaluation. If your suspicions are confirmed, a certified sweep will
be able to make recommendations about how to bring the system back
into compliance with safety standards. Depending on the situation,
you might need a few flue tiles replaced, a relining system
installed or an entire chimney rebuilt. Each situation is unique and
will dictate its own solution.
What to Do if You Have a Chimney
If you realize a chimney fire is
occurring, follow these steps:
1) Get everyone out of the house,
2) Call the fire department
If you can do so without risk to
yourself, these additional steps may help save your home. Remember,
however, that homes are replaceable, but lives are not:
- Put a chimney fire extinguisher into
the fireplace or wood stove
- Close the glass doors on the
- Close the air inlets on the wood
- Use a garden hose to spray down the
roof (not the chimney) so the fire won't spread to the rest of the
- Monitor the exterior chimney
temperature throughout the house for at least 2 or 3 hours after
the fire is out
Once it's over, call a Professional Chimney Sweep to inspect for damage. Chimney fire damage
and repair normally is covered by homeowner insurance policies.