Gas fireplace humming? Cracked liner symptoms to watch for
Five subtle signs your flue is failing — before the carbon monoxide alarm proves it. Written for Ohio homeowners running gas inserts.
1. Persistent humming or pressure imbalance
A cracked liner changes the draft, and the appliance has to work harder to vent. That extra effort often shows up as a low hum or whistle when the burner is running.
2. Soot stains above the firebox
Vertical black streaks on the surround mean flue gases are escaping where they shouldn't be.
3. White, chalky residue on the brick
Efflorescence — salts deposited as moisture moves through cracked masonry. Almost always points to a compromised liner or crown.
4. Cold air falling into the room
Downdraft when the appliance is off can mean the flue is no longer sealed properly.
5. A CO detector that won't stop chirping
Treat this as an emergency. Shut the appliance down, open windows, and call us — or 911 if anyone feels symptoms.
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