Smell From Chimney: Causes and How to Get Rid of It
Updated · By the Roof to Footing editors
A smell from the chimney is most often creosote, the tarry residue that wood smoke leaves in the flue. It smells like a campfire that went out days ago, and it's usually worst in hot, humid summer weather or after rain. Two things make it reach the room: moisture that brings the odor out of the deposits, and air flowing down the chimney into the house instead of up. Fixing the smell means removing the source and stopping that downdraft.
Common causes
| What it smells like | Likely cause |
|---|---|
| Smoky, tarry, like an old campfire | Creosote in the flue, stronger in heat and humidity |
| Musty, damp, like a wet basement | Water getting in: missing cap, cracked crown, leaky chase cover or flashing |
| Rotten, foul | An animal or bird died in the chimney, or debris from nests |
| Smoke right after lighting a fire | Damper closed, cold flue, or the house pulling air down the chimney |
| Gas or rotten egg odor | Possible gas leak. Leave the house and call the gas company |
Why it's worse in summer
Creosote absorbs moisture. On humid days it releases more odor. At the same time, the house often runs exhaust fans and air conditioning while the chimney is cool, and the house can pull air down the flue rather than up. That brings the smell right into the room.
Negative pressure: the house pulling air down
Modern houses are tighter, and they have kitchen range hoods, bathroom fans and clothes dryers pushing air out. That air has to be replaced from somewhere, and an open chimney is an easy path. Clues that pressure is the issue: the smell gets stronger when the range hood or dryer runs, and a strip of tissue held at the fireplace opening gets pulled into the room.
Fixes, from simplest to most involved
- Have the chimney swept. Removing creosote removes most of the odor source. This is also a fire-safety task you should do annually if you burn wood.
- Close the damper when the fireplace isn't in use, and check it seals. A warped throat damper leaks; a top-sealing damper stops air movement much better.
- Install a chimney cap to keep rain and animals out.
- Fix water entry. A cracked crown or rusted chase cover lets water in, which feeds musty odors and damages the flue.
- Close glass doors on the fireplace, or use a fireplace draft stopper (a removable inflatable plug, which you must remove before any fire).
- Balance the house's air. Crack a window when running a big range hood, or ask an HVAC contractor about makeup air for large exhaust fans.
- Absorb what's left. Baking soda or activated charcoal in a tray inside the firebox can soak up mild odors between sweepings.
When to call a pro
Call a chimney sweep certified by an organization such as CSIA if the smell persists after cleaning, if you see glazed or shiny creosote in the flue (a fire hazard that needs special removal), if there's water in the firebox, or if you suspect an animal. Call the gas utility right away for any gas smell.