How do you fix a damaged chimney flue?
Short answer. A damaged chimney flue is usually fixed by relining it: a stainless steel liner sized to the appliance is the most common repair, a cast-in-place liner can restore an old or irregular flue, and cracked clay tiles near the top are sometimes replaced. Flue repair affects fire safety and carbon monoxide, so it belongs to a certified chimney professional, starting with a camera inspection.
What goes wrong with flues
- Cracked clay tiles from a chimney fire, overheating or years of heat cycling.
- Open mortar joints between tiles that let heat and gases into the masonry.
- Spalled or crumbling tiles from water entering through a missing cap or cracked crown.
- No liner at all in some older homes.
- The wrong size for a new stove or gas insert, which hurts draft and builds creosote or condensation.
Repair options
- Stainless steel liner. A rigid or flexible stainless pipe run down the existing flue, sized to the appliance, often insulated, with a top plate and cap. Standard for stove inserts and gas conversions.
- Cast-in-place liner. A cement-based material formed inside the flue, which can also strengthen old masonry.
- Tile replacement. Possible for damaged tiles near the top, but hard lower down.
- Resurfacing systems that coat the inside of a gapped flue, applied by trained installers.
Order of operations
- Stop using the appliance if damage is suspected.
- Get a Level 2 inspection with a camera scan from a sweep certified by the Chimney Safety Institute of America.
- Fix the water source at the top: cap, crown and flashing. Water is a common cause of tile damage.
- Reline to the appliance's requirements, and keep the paperwork.
Some jurisdictions require a permit for relining, so ask your installer. For the roof side of the chimney, see chimney leaks and crickets and roof flashing explained.