Chimney Sweep And Creosote

February 28, 2023

Creosote is a combustible deposit that is created from condensed wood smoke, tar, condensed vapors and other organic compounds. Flue gases containing hydrocarbons, tar droplets (tar fog), and other combustible gases are a direct result of incomplete combustion. Tar droplets and invisible vapors condense as a liquid onto the chimney system.

While the creosote continues to build upon itself, the collected deposits may appear in several forms:

Flaky granules
Hard, slag like deposits
Soft and dusty accumulations

Factors that affect creosote:

Smoke density
Moisture content: wood with high moisture content (typically wood will have a high moisture content if it is freshly cut, and this moisture can make up unto 50% of the weight of the wood) keeps combustion temperatures low resulting in the release of harmful gases.
Flue gas temperatures: influenced by the chimney type, size and location. Uninsulated masonry chimneys located on exterior walls are colder inside and out than interior masonry chimneys. Cold chimney walls will cool flue gases causing them to condense and deposit creosote on chimney liners.
Large fuel loads: large fuel loads can also have the effect of increasing creosote accumulation. When large amounts of wood are present in the firebox more smoke is generated and less oxygen is available for complete combustion to occur.