Does My Chimney Need a New Liner?
Not every chimney needs a liner replacement. Here is how to know whether yours does.
Reviewed by John Freeman, chimney and fireplace professional with 20+ years of field experience.
Last updated
Short Answer
Not every chimney needs a new liner. A liner is needed when the existing one is cracked, gapped, or deteriorated; when a masonry chimney was never lined; or when a new appliance, such as a wood stove insert, needs a different type or size of flue. The Oregon Residential Specialty Code requires masonry chimneys to be lined. Whether yours needs replacing should rest on what an inspection can see, not on the age of the chimney.
What a Liner Does
The liner is the inner flue that carries smoke and combustion gases out of the house. The Oregon Residential Specialty Code requires the lining to resist corrosion, erosion, softening, or cracking from flue gases and condensate at temperatures up to 1,800 degrees F. The Chimney Safety Institute of America (CSIA) says masonry chimney fires burn at around 2000 degrees F, hot enough to melt mortar, crack tiles, and cause liners to collapse. CSIA also lists damaged or deteriorating flue liners among the venting problems that let toxic gases into living spaces.
Signs a Liner Needs Attention
| What is found | What it can mean |
|---|---|
| Cracked, spalled, or offset flue tiles, or missing mortar between tiles | CSIA tells inspectors to note these as visible liner defects. In a chimney fire, CSIA says cracked tiles and displaced mortar give flames a pathway to the wood frame of the house. |
| Signs of a past chimney fire: puffy or honeycombed creosote, cracked or collapsed tiles, a warped damper | CSIA says most chimney fires go undetected, and its procedures call for a Level 2 inspection when there are signs of one. |
| Smoke or heat escaping through mortar or tile joints | CSIA lists smoke escaping through mortar joints of masonry or tile liners among the signs of chimney fire damage. |
| No liner | CSIA distinguishes older unlined flues from tile-lined ones that meet current codes, so unlined chimneys exist. Current code requires masonry chimneys to be lined. |
| A flue that is the wrong size or type for the appliance | The code says the lining must suit the connected appliance, and that the flue may not be smaller than the appliance connector. CSIA notes that many chimneys are improperly sized for the appliances they serve. |
| Corrosion or moisture from a newer gas furnace vented into an old flue | CSIA says high-efficiency gas furnaces produce flue gases with high water vapor content and chlorides, which makes conditions in older flues more corrosive. |
Liner Options
The code accepts clay flue lining that meets ASTM C315, listed and labeled chimney lining systems under UL 1777, factory-built chimneys listed for installation inside masonry, and other approved materials that resist corrosion, erosion, softening, and cracking at temperatures up to 1,800 degrees F. In residential retrofits the common choices are stainless steel and cast-in-place.
| Type | Notes |
|---|---|
| Clay tile | The liner in many masonry chimneys. CSIA checks that tiles are intact, have mortar between them, and are supported on all four sides. |
| Stainless steel | Installed inside the existing flue. CSIA recommends insulating every liner that serves a wood-burning appliance. |
| Cast-in-place | A lining formed in place inside the existing flue. |
When a New Appliance Changes the Answer
A liner that was fine for an open fireplace can be wrong for a wood stove or insert. NFPA 211 calls for a Level 2 inspection when an appliance is added or changed and before a flue is relined. The code says the lining has to suit the connected appliance, following its listing and the manufacturer's instructions. EPA says a certified installer makes sure the liner in a masonry chimney is installed correctly when an insert goes in, and CSIA says liners serving solid-fuel appliances need to be insulated.
Before You Commit
Liner replacement is significant work, so the recommendation should rest on evidence you can see. Ask to see the photos or video of the defect. NFPA 211 calls for a Level 2 inspection before a flue is relined, and that level includes examining the inside of the flues with video scanning or other means, so the evidence should exist. If you were told you need a new liner, a second look is reasonable.
If you are in Southern Oregon, a $99 inspection will tell you what condition the liner is in. We photograph what we find and show you, and any repair is quoted in writing before work begins.
Sources
- Oregon Residential Specialty Code (2023), Chapter 10: Chimneys and Fireplaces
- Chimney Safety Institute of America: Preventing Chimney Fires
- Chimney Safety Institute of America: Avoiding Carbon Monoxide Hazards
- CSIA Standard Operating Procedure: Level 1 Inspection, Masonry Fireplace
- Chimney Safety Institute of America: Homeowner FAQs
- NFPA 211, Chapter 15: Inspection of Existing Chimneys (committee input for the next edition)
- US EPA Burn Wise: Choosing Wood-Burning Appliances
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