Which chimney problems are dangerous?
Short answer. The dangerous chimney problems are the ones that can start a fire, push carbon monoxide into the house, or drop masonry: heavy or glazed creosote, a cracked or missing flue liner, a blocked flue, and a chimney that leans, separates from the house or sheds bricks. Long-term leaks that rot the framing around a chimney are a slower but real structural hazard.
Fire and carbon monoxide hazards
- Creosote buildup. Wood smoke leaves a tar-like deposit in the flue. Shiny, glazed creosote is the most flammable stage and needs a certified sweep.
- A cracked, gapped or missing flue liner. Heat can reach wood framing through cracks, and flue gases can leak into rooms. Some older homes have unlined chimneys.
- A blocked flue. Nests, fallen debris or collapsed liner tiles can back smoke and carbon monoxide into the house. A furnace or water heater sharing a flue makes this especially serious.
- Warning signs: smoke spilling into the room, a strong odor, headaches when appliances run, or a carbon monoxide alarm. Stop using the appliance and get it inspected.
Structural and falling hazards
- Leaning or pulling away from the house, often from a settling footing. A visible gap at the wall is a stop and call sign.
- Loose or spalling bricks and a crumbling crown, which can fall onto the roof, a walkway or a car.
- A rusted, loose cap that can blow off in a storm.
- Rot around the chimney. Years of slow flashing leaks soften the decking and framing next to the chimney, and a soft spot there can give way under a person's weight.
Who handles what
A sweep certified by the Chimney Safety Institute of America handles the flue, liner and creosote. A mason handles leaning or crumbling masonry. A roofer handles the flashing, the cricket and any rotted decking where the chimney meets the roof. Keep working carbon monoxide alarms near sleeping areas in any home with fuel-burning appliances. For the roof side, see chimney leaks and crickets and roof flashing explained.