FYI: Creosote and Soot

I found this on a wood stove website, and thought I'd share
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http://www.cunninghamgas.com/Rutland/creoedit.htm


Controlling Creosote and Soot Buildup

Creosote is simply unburned wood particles and condensed flue gases which deposit in the chimney interior. The rate of creosote buildup is affected by residence time, smoke density, and stack temperature.

Residence Time
Residence time is the time the smoke remains in the venting system. Residence time is affected mainly by flow. Flow is simplythe amount of air moving through the chimney. Within certain limits, the greater the air movement, the lower the residence time will be. Abnormallyhigh 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 combustionresulting in high smoke density. Creosote is simply unburned particulates and gases leaving the fire. When smoke density is high, creosote depositswill 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 (Chimney) Temperature
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 besubjected 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.

Types Of Chimney Deposits
Chimney deposits can be found in a variety of forms but can be divided into three basic types as shown below:

Soot
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 noncombustible.

Creosote
Creosote can be defined as a combustible deposit in the venting system which begins as condensed wood smoke including tar fogs and vapors. Creosote is a by-product of incomplete combustion. 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 deposits or bubbly deposits in the venting system. Creosote is flammable.

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.