Creosote - What is it and How Can I get Rid of it?
By definition, creosote is simply unburned wood particles
and condensed flue gases which deposit on the inside of the chimney.
The creosote forms as the flue gases exit the fireplace or wood stove,
and draft upward into the relatively cold flue where condensation occurs
and begins to solidify. This results in carbon based condensation that
materializes inside the flue and becomes creosote.
As creosote builds on the chimney interior, it goes
through three stages and becomes more and more of a fire hazard as it
goes through each stage. All three stages of creosote can exist
in one chimney, and no matter if you have one or all three it's highly
combustible. If allowed to build up in sufficient quantities, and ignite
inside the chimney flue, the result is a volcanic chimney fire.
This article discusses the three stages of creosote build up and which
products are most effective to get rid of it before it causes damage
to your property and family.
Stage 1 creosote build
up is known as soot and is identified as fine, silky, black dust
Soot is primarily composed
of unburned carbon particles but may also contain ash. Soot has
a soft texture and will be black or brown in color. The flammability
of soot will depend on the concentration of soot and ash. Soot,
since it is made of carbon, is combustible. Ash is non-combustible.
Stage 2 creosote build up is known as creosote and is identified
as porous and crunchy
Creosote can be defined
as a combustible deposit in the venting system. Creosote is a by-product
of incomplete combustion, which begins as condensed wood smoke including
tar, fogs and vapors. If a fuel is fully burned there will be no
smoke and, therefore, no creosote. Creosote will be hard brown or
black and form either curly, flaky or bubbly deposits in the venting
system all of which are flammable.
Stage 3 creosote build up is known as glaze and can be identified
as drippy, sticky, shiny glaze
Glaze is a form of deposit
that presents itself as a shiny, tarry substance. Glaze can form
puddles or drop down and make formations that resemble black icicles.
Glaze is the densest type of chimney deposit and, therefore, represents
the greatest amount of fuel to burn in the event of a chimney fire.
Glaze is also the most difficult type of deposit to remove from
the chimney.
Residence Time - Residence time is the time
the smoke remains in the venting system. Residence time is affected
mainly by flow. Flow is simply the amount of air moving through the
chimney. Within certain limits, the greater the air movement, the lower
the residence time will be. Abnormally high flow can result in turbulence,
which can actually increase residence time. Low flow, usually caused
by oversized flues, results in longer residence time and high rates
of creosote buildup. The less time the smoke stays in the chimney, the
less it can deposit on the walls. This is desirable for maintaining
a clean chimney.
Smoke Density - Smoke density is the amount
of smoke produced by the fire. When combustion air is restricted, it
causes incomplete combustion resulting in high smoke density. Creosote
is simply unburned particulates and gases leaving the fire. When smoke
density is high, creosote deposits will be high. Without smoke there
is no creosote. If you can visualize an open campfire, it generally
produces very little smoke because it has plenty of air to complete
the combustion process. With complete combustion there is no smoke and
no creosote. Stack temperature is the temperature of the interior walls
of the chimney. Stack temperature is affected by the amount of heat
allowed to go up the chimney. The warmer the walls of the chimney the
less the creosote can adhere to them. Stack temperature is also affected
by the size and location of the chimney. If the chimney is on an exterior
wall as opposed to an interior wall, it will constantly be subjected
to outside cooling effects. If the chimney is oversized, it will require
more heat to keep the surface walls warm due to the increased mass.
With this thought in mind, you can see how a very large chimney that
will never fully warm up would have the potential to cause excessive
creosote deposits.
Prevent excess creosote build up and chimney fires by following these
simple tips in our article for
Proper Chimney Venting.
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