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November 22, 2008
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Chimney Problems
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MSU Extension
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What's in this article
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 Introduction
Creosote
Reducing creosote problems
Be Prepared for A Chimney Fire
If you have a chimney fire
Chimney Cleaning
Cleaning the Chimney Yourself
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 Return to the Knowledge Base
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Be Prepared for A Chimney Fire
No wood burning system is 100% safe and fire-proof. A
safe installation and extra care help prevent fire, but
accept the idea that there could be a fire, and be
prepared to handle it. 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.
Make certain everyone in the house is familiar with
the warning signs of a chimney fire --- sucking sounds, a
loud roar and shaking pipes. Instruct everyone on what to
do in case of fire. Practice fire drills and instruct all
adults on how and when to use a fire extinguisher. Put
the fire department phone number in an obvious place near
the phone.
If you have a chimney fire:
a) Call the fire department immediately.
b) If all the stove pipe joints are tight and no other
appliance is connected to the same flue, close all
openings and draft controls if you have an air-tight
stove. Close the stove pipe damper in a non-air-tight
stove.
c) You can attempt to cut off the air supply to a
fireplace by using a wet blanket or sheet metal to seal
off the fireplace opening. Be careful since a strong draft
can make this difficult and dangerous. Use only non
combustible materials.
d) If you have a leaky stove or fireplace you may have to
wait for the fire to burn out.
e) Get everyone out of the house, and put them to work
watching for sparks or signs of fire on the roof or
nearby. One adult should stay in the house to check the
attic and upper floors for signs of fire.
f) Discharge a class ABC dry chemical fire extinguisher or
throw baking soda into the stove or fireplace if the
chimney is not sound or there is a danger of the house or
surroundings catching on fire. The chemical travels up
the chimney and often extinguishes the flame.
g) Throwing water in a stove will cause the metal to warp,
but if it's a choice between the house or the stove, use
water.
h) Check the chimney after a fire. A chimney fire can
range from 2000 to 3000 degrees F which is hot enough to
cause deterioration of metal or cause masonry to weaken.
Metal chimneys can deteriorate after 2 or 3 fires.
i) If a chimney fire occurs once, chances are that it will
occur again. Find the cause.
A problem with frequent chimney fires is the
possibility of the framing catching on fire. The ignition
temperature of new house framing is about 500 degrees F.
Over a period of years, as this wood is repeatedly heated
by chimney fires, the wood will ignite at a much lower
temperature.
Chimney Cleaning
Chimneys need to be cleaned to remove creosote and
soot deposits. This will prevent chimney fires and
improve the draft as well. How often the chimney is
cleaned depends on how frequently the wood burning
appliance is used, how it is operated and the type of
installation. Some authorities recommend cleaning the
chimney after every third cord of wood is burned and most
recommend at least once a year. Any time you observe
excessive soot and creosote, the chimney should be
cleaned. After you once have cleaned the chimney, you may
want to check it after 2 weeks, 1 month, 2 months,
etc., to determine how often your chimney needs to be
cleaned.
You may have the chimney cleaned for you by
professional chimney sweeps or you can clean it yourself.
Costs for chimney sweeps vary with the job but usually
amount to about $40. ln addition to cleaning your
chimney, a good chimney sweep can act as a inspector for
your installation.
 Figure 2 - Common Chimney Brushes |
Chimneys are normally cleaned by mechanical means to
scrape off any loose creosote build-up. Stiff wire chimney
cleaning brushes are available at reasonable cost.
(See Figure 2) They are constructed to match the size of the
chimney flue and can be pushed through the chimney with
extension rods or pipe or can be pulled with ropes on
either end of the brush. You can attach a weight to the
bottom of some brushes. The weight will drag the brush to
the bottom of the chimney so it can be pulled up with a
rope. Other cleaning methods are to lower a burlap
bag containing wire netting weighted with chains or rocks
up and down the chimney or to use tire chains or wire
netting without a bag. (See Figure 3)Don't swing a length of
heavy chain down the chimney. The impact can damage the
flue lining.
 Figure 3 - Chimneys can be cleaned with a bag filled with rocks or chains or with a professional stiff wire brush |
Many people start chimney fires deliberately by
building hot fires or by tossing in compounds designed to
remove soot and creosote by controlled burns. Under some
circumstances this practice may be reasonable, but
generally it is a risky way to keep a chimney clean. Any
chimney fire could build into a house fire, but in
addition a chimney fire causes wear on a chimney. The
high temperatures increase corrosion rate of metals and
cause thermal expansion of masonry materials which can
lead to cracks. Some of the compounds used in controlled
burns have been known to explode in stoves.
Chemical chimney cleaners are commercially available.
These are not intended for use in chimneys already
containing heavy deposits of soot and creosote. Chemicals
such as sodium chloride, or table salt, are sometimes
used as a chimney cleaner. These chemicals combine with
water released from a hot fire to form a weak acid that
dissolves small amounts of creosote. Sodium chloride is
corrosive to metal and is not recommended for metal
chimneys. Cleaners that contain copper sulfate will coat
any soot in the chimney and act as a catalyst to allow
soot to burn away at lower than normal temperatures.
Chemical cleaners are intended to be used after
chimneys are cleaned or new. Use the chemicals as
directed--- approximately 1 ounce per week. If not used
as directed, the chemicals can cause intense chimney
fires that will result in rapid deterioration of the
chimney. THE ONLY EFFICIENT AND EFFECTIVE METHOD OF
CLEANING IS TO USE A CHIMNEY BRUSH, SINCE THE BRUSH
SCRUBS THE ENTIRE SURFACE UNIFORMLY.
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