Blocked flues and failed liners are a leading cause of CO in the home. What raises the risk and how to eliminate it.
Your chimney's job is to move combustion gases out of the house. When it cannot, those gases — including carbon monoxide, which is colorless and odorless — come back into your living space.
Chimney conditions that raise the risk
- Animal nests, leaves or debris blocking the flue
- Heavy creosote narrowing the flue
- A collapsed or cracked liner
- A flue sized wrong for the appliance after a conversion
- A blocked direct-vent termination on a gas fireplace or furnace
- A closed or stuck damper
- Negative pressure from range hoods, bath fans or a dryer in a tightly sealed home
Symptoms to take seriously
Headache, dizziness, nausea, confusion and fatigue that improve when you leave the house. If multiple people or pets feel unwell at the same time, get everyone outside and call 911 before anything else.
Detectors
- One CO detector on every level, including the basement
- One within 10 feet of each sleeping area
- Not directly above a fireplace or fuel-burning appliance — you will get nuisance alarms
- Test monthly, replace batteries yearly and replace units every 5–7 years
An annual inspection is the practical defense. It finds blockages, liner failures and venting problems before they become a CO event.
Frequently Asked Questions
Can a dirty chimney cause carbon monoxide?
Yes. Creosote buildup and blockages restrict the flue, which prevents combustion gases including carbon monoxide from venting out of the home.
Do gas fireplaces produce carbon monoxide?
Any fuel-burning appliance can, particularly when combustion is incomplete or the vent is blocked. Annual service and CO detectors are essential with gas appliances.
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