What Is Creosote — and Why Is It Dangerous?

By Eagle Chimney MN · October 13, 2026

Every wood fire leaves creosote behind in your flue. Here's what it is, the three stages it goes through, and how to keep it from becoming a chimney fire.

Creosote starts as smoke

When wood burns, it releases gases and particles. As those gases rise and cool inside the flue, they condense on the liner walls as creosote — a dark, tarry substance that builds up a little with every single fire. There's no way to burn wood with zero creosote; there is only managing how fast it accumulates and removing it on schedule.

The three stages

Stage 1 creosote is flaky and soot-like — it brushes away easily and is what a routine sweep handles. Stage 2 turns tarry and crunchy, forming hard flakes that need more aggressive removal. Stage 3 is glazed creosote: a shiny, hardened coating that looks like tar poured down the flue. It's the most concentrated fuel of the three, the hardest to remove, and it forms fastest when burning wet or unseasoned wood in a cool flue.

Why it's a fire risk

Creosote is combustible — that's the whole problem. A chimney fire ignites when flue temperatures climb high enough to set the accumulated creosote burning. Chimney fires can crack liners, damage masonry and, in the worst cases, spread to the home itself. Even a small, contained chimney fire you never noticed can crack a liner and leave the chimney unsafe for the next fire. That's why 'we had a chimney fire but it seems fine' always deserves an inspection.

Keeping buildup slow

Burn dry, seasoned hardwood; keep fires hot rather than smoldering; and never burn trash, cardboard or treated wood. Then pair good habits with the thing that actually controls the risk: an annual inspection, and a professional sweep whenever buildup calls for it. If you're not sure how much creosote is in your flue right now, an inspection will tell you.