How to spot creosote buildup in your chimney
Stage 3 creosote is what burns down houses. You can spot it from the firebox if you know what to look for.
What you'll learn
- The three stages of creosote (sooty, crusty, glazed) and what each looks like
- How to safely inspect the smoke shelf with a flashlight from the firebox
- When buildup is past DIY removal and needs rotary chains or PCR chemical treatment
- Why burning hot fires of seasoned wood prevents most buildup
Step by step
- Wait 24+ hours after the last fire so everything is fully cool.
- Open the damper fully and shine a bright flashlight up past it.
- Look at the smoke shelf — the flat ledge just inside the damper.
- Stage 1: black, dusty, brushable. Stage 2: crusty flakes you can chip off.
- Stage 3: shiny black glaze fused to the flue tile. Stop and call.
Safety note
If you see Stage 3 glazed creosote — or anything you are not sure about — do not light another fire until a CSIA-trained sweep inspects the flue. Stage 3 creosote causes most chimney fires.
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