If you burn wood, you make creosote. It is the dark, tarry residue that condenses on the inside of a flue as smoke cools, and it is the fuel behind most chimney fires. In Westchester, where many of the original brick homes still have working wood-burning fireplaces, understanding creosote is the single best way to keep your chimney safe.
Creosote is not all the same. It builds in three stages, and the stage yours is at decides how easily it can be removed.
What creosote is
As wood burns, it releases smoke made of gases, water vapor and unburned particles. When that smoke meets the cooler upper walls of your flue, it condenses and sticks. Over many fires this residue hardens. The cooler and slower your fires, the faster creosote forms.
The three stages
Sweeps grade creosote by how hard it is to remove. Stage one is a light, flaky soot that brushes away easily. Stage two is a crunchy, tar-like flake that needs more aggressive tools. Stage three is a hard, shiny glaze that is highly flammable and very difficult to remove.
- Stage 1: light, dusty, easily brushed away
- Stage 2: hard, flaky, tar-like deposits
- Stage 3: shiny glazed tar, extremely flammable
What speeds up buildup
Several habits raise creosote fast. Burning unseasoned or wet wood, damping the fire down low overnight for a slow burn, and a flue that runs cold all encourage smoke to condense. Seasoned hardwood, hotter fires and a properly sized liner keep buildup to a minimum.
When to sweep
A common guideline is to sweep after every cord of wood burned, or at least once a year before the heating season. If you see stage two or three deposits, or you smell a strong tarry odor on warm days, do not wait. Glazed creosote is what turns a normal fire into a chimney fire.
The classic brick homes we clean through our chimney sweep service in Westchester were built for wood fires, and wood fires always leave creosote behind.
Heavy creosote in your Westchester chimney? Book a sweep.
Frequently asked questions
How often should I have my chimney swept?
A good rule is once a year, or after every cord of wood burned. Homes that burn often may need more frequent sweeping.
Can I just burn a creosote-sweeping log instead of a sweep?
No. Those logs may loosen some light creosote but they do not clean the flue or inspect it. They are not a substitute for a professional sweep.
Is stage three glazed creosote removable?
It is difficult. It often requires special tools or chemical treatment, and sometimes several visits. Preventing it with regular sweeping is far easier.
Does a gas fireplace produce creosote?
Gas produces very little creosote, but gas flues still need inspection for blockages, moisture and corrosion.
By Adam Evans, owner of Chimney Sweep Brothers, with 12 years of chimney and venting experience in La Grange and the western suburbs.
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