What a cracked flue tile actually does
Many masonry chimneys are lined with square or rectangular clay tiles stacked from the smoke chamber to the top. That liner has three jobs. It contains heat so it can't reach nearby framing. It carries smoke and gases up and out. It also protects the brick from acidic combustion byproducts. When flue tiles crack or the joints between them open, all three jobs suffer:
- Heat transfer. Hot gases and embers can reach the brick and, through gaps, wood framing near the chimney.
- Gas leakage. Smoke and carbon monoxide can find their way into attics, walls or rooms, especially from a furnace or boiler that shares the chimney.
- Faster decay. Moisture and acidic condensation soak into the masonry. This can eventually show up outside as cracked chimney brick.
What happens during the visit
A chimney fire or years of acidic gas exhaust can crack and erode tile liners. A cracked or separated liner lets heat reach the masonry and nearby framing, and exhaust can leak through.
Scan the flue
A camera shows cracks, gaps and missing sections along the full length.
Size the liner
The appliance and the flue decide the liner type and diameter.
Install
The liner is fed from the top, connected at the bottom, and capped and sealed at the top.
Confirm
Draft is checked and you're shown the scan and the finished work.
What the technician checks
- Missing or displaced sections
- Liner size against the appliance
- Signs of a past chimney fire
- Top plate, cap and seal
- Connection at the appliance or smoke chamber
- Tile cracks and joint gaps
Carbon monoxide
A damaged liner can let exhaust into the home. If a carbon monoxide alarm sounds or anyone feels dizzy or sick, get everyone outside and call 911.
When to book cracked flue tile
- A chimney fire in the past
- A new insert or stove that needs a matched liner
- Pieces of clay tile in the firebox or at the bottom of the flue
- Cracks or open joints seen in a camera scan
- Smoke or a smell in rooms next to the chimney
Warning signs of cracked flue tiles
You can't see most of the flue from inside the house, but these clues are worth taking seriously:
Clues that point to flue tile damage
01Tile pieces in the firebox
- What you may notice
- Curved or flat pieces of terra cotta mixed with ash or sitting on the smoke shelf
- How it’s confirmed
- The pieces are matched to the liner, then the flue is examined from top and bottom
02Heavy glaze or soot
- What you may notice
- Thick, shiny buildup that hides the tile surface and joints
- How it’s confirmed
- The flue is cleaned first so cracks and open joints can actually be seen
03After a chimney fire
- What you may notice
- Loud rumbling, dense smoke from the top, or puffy, flaky creosote afterward
- How it’s confirmed
- The full liner length is inspected before the next fire, since chimney fires commonly crack tiles
Smoke where it shouldn't be
If you smell smoke in rooms away from the fireplace, or a carbon monoxide alarm sounds, stop using the appliance, get everyone into fresh air and call emergency services. Emergency calls about the chimney itself are accepted at any hour, Sunday through Friday.
Confirming the damage before anything is repaired
A flashlight from the firebox shows only the bottom few feet of the flue. The reliable way to judge cracked flue tiles is to run a camera through the full length of the flue, ideally right after a flue cleaning service removes the soot that hides fine cracks. The footage shows where the cracks are, how many tiles are affected, and whether joints have separated.
A camera-based flue inspection gives you something concrete to look at instead of a guess. Repair options range from fixing individual sections to installing a new liner. The page on fixing cracked chimney flue tile covers them in detail. For background on how liner damage relates to other chimney trouble, see this overview of common chimney issues and a rundown of common chimney problems.
