Chimney Problems
The combustion process when wood is burned is never
complete. The smoke from a wood fire usually contains a
dark brown or black substance which has an unpleasant
odor. This tar-like substance is called creosote and is
found almost anywhere in a wood heating system.
At temperatures below 250 degrees F creosote will
condense on the surfaces of stove pipes or chimney flues.
When the temperature gets below 150 degrees F the
creosote deposit will be thick, sticky and similar to
tar. This tends to trap carbon from smoke which dries and
bakes inside pipes and flues. This flaky substance is
very flammable.
Creosote is more of a problem with wood stoves than
fireplaces since the exhaust gases from stoves are cooler
than those from the fireplaces.
The amount of creosote condensing on the surfaces of
the system varies according to the density of the smoke
and vapor from the fire (less smoke means less creosote),
the temperature of the surface on which it is condensing
(higher temperatures reduce chance of creosote
condensation) and the type and dryness of wood being
burned. Creosote may build up to a considerable
thickness on the interior surface of the chimney and the
draft opening may subsequently be reduced. A serious fire
may be ignited if creosote is allowed to build up. Most
problems with creosote are due to poor chimneys with a
low draft and cold walls.
You can reduce the creosote problem several ways.
Smoke density can be lowered somewhat in an airtight
stove by using small amounts of wood and stoking more
often or by using larger pieces of wood. Creosote
formation can be limited by leaving the air inlet or
stove door slightly open after adding wood to promote
more rapid burning until the wood is mostly reduced to
charcoal. Then close the inlet as desired.
Allowing this extra air causes more complete
combustion lowers the potential creosote-forming gases and
generates additional heat to the surrounding area. Vapor
in the flue gases may be controlled by using the driest
wood possible and using only small pieces of wood during
mild weather when combustion is relatively slow. The stack
temperature can be raised by insulating the stove pipe
connection so that it cools as little as possible before
reaching the chimney. Using an insulated pipe also aids
in increasing the stack temperature.
Draft can be increased by having as few bends as
possible between the appliance and the chimney, having
the proper height and diameter, keeping the chimney in
good repair and by having a separate flue for each
appliance. Also use proper sized stove pipe. In a large
chimney, draft can be increased by decreasing the flue
size. This can be done by installing a new smaller flue
or a stainless steel stove pipe liner.
In many airtight stoves, a sealed overnight fire will
deposit creosote even with dry hardwood. To dry the
creosote always open the draft caps and let the fire burn
hot for at least 5 minutes every morning and again before
bedtime.
Opening the direct draft damper 20 to 30 minutes to
dry the creosote in chimneys is a questionable practice.
This should only be done in a new or clean chimney and
should be done daily or every time you use the wood stove.
Allowing hot flame in the chimney at intermittent times
can result in a small chimney fire. The heat generated
from these hot flames also may cause deterioration of the
metal or crack mortar in the chimneys.
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.
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.
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. Don't swing a length of
heavy chain down the chimney. The impact can damage the
flue lining.
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.
Cleaning the Chimney Yourself
If you plan to clean the chimney yourself, you will
need to obtain some or all of the following tools and
supplies:
Drop cloth or other appropriate covering
Treble light or portable lantern
Leather gloves
Hand wire brush
Hand scraper or stiff putty knife
Hammer and screwdriver
Heavy duty vacuum cleaner
Whisk broom and dust pan
Metal bucket
Small shovel
Adjustable wrench
Can of furnace cement
Chimney brush
Rope and a weight or extension rods
Before starting to clean the chimney, be sure all
doors and windows are shut to prevent any drafts. Remove
damper, if possible. Seal fireplace opening with a drop
cloth and masking tape. You will need proper protective
clothing, including a mask to cover your mouth and nose
and glasses or goggles for your eyes. The material that
collects in chimneys is of such a nature that you should
avoid contact with it as much as possible. Wear good shoes
with slip resistant soles and be careful when climbing on
high, steep roofs to clean a chimney.
When cleaning the chimney from the roof, the easiest
method is to attach a line to the brush with a weight on
the opposite end. This weight should be of such a size and
shape that it cannot swing free into the tile liners and
cause damage. The purpose of the weight is to pull the
brush down into the chimney. A solid 15- to 20-pound
weight is required to move the brush downward. This will
depend on how tightly the brush fits and how dirty the
chimney is.
Another method is to attach a rope at each end of the
brush with a person at the top of the chimney and one at
the bottom, taking turns pulling the rope. This method may
be somewhat messy.
More effective is the use of rigid extensions such as
a pipe or tubing with a flexible leader. This allows you
to control and feel the scrubbing action of the brush in
the chimney. This method is used by most professional
chimney sweeps. Fiberglass rods are available for this
purpose. If metal pipe is used, be careful of power lines
above.
Lower the brush into the chimney being careful not
to disturb any loose brick mortar or any device in the
chimney. Cleaning can be accomplished by passing the
brush through the chimney a number of times in the same
direction or by raising and lowering the brush in short
strokes in a scrubbing action. If your brush is too
large, it will not reverse in the chimney and may even
lock up.
Experience will tell you how many passes to make
to get the chimney clean. Once this process is finished,
remove the seal from the fireplace opening. Use a drop
cloth in your working area. Slowly open the damper if you
were unable to remove it, vacuum up debris from the
bottom of the hearth, smoke shelf or catch pit. If you
can't open the damper you may have to drop a hose down
the chimney to vacuum out the soot.
While cleaning masonry chimneys, check for cracks in
the brick or masonry. Cracks allow cool air to come in,
thus reducing the efficiency of the fireplace or wood
stove and allowing creosote to form.
Stove pipes on the wood burner are critical to safety
and require additional attention. When cleaning an inside
flue, remove the connected sections. Be careful to
protect the area from soot. Take the sections outdoors
and brush inside them with a hand wire brush or a flue or
chimney brush that is the same diameter as the pipe.
Remove all the soot and creosote build-up from the breech
and the loose accumulation in the fire box. Stove pipes
need to be cleaned regularly. Check pipes at least once
every 2 or 3 months of stove operation.
After using your chimney brush, rinse it in a
cleaning solution such as kerosene and store it away in a
dry place. lt is a valuable tool.