· Michael Blair
A liner contains heat and combustion products within the flue. Older Nashville chimneys frequently have clay tile that has cracked, or in the oldest cases no liner at all.
What a liner does
Contains the heat so it does not reach the surrounding masonry and framing, contains acidic combustion products so they do not attack the mortar, and provides the correct flue size for the appliance.
A cracked or missing liner defeats all three, and the third matters more than people expect — an oversized flue cools smoke and accelerates creosote.
When relining is needed
Cracked, spalled or displaced clay tiles found on inspection. After a chimney fire, which commonly cracks tiles. When changing the appliance, since a new stove or gas insert usually needs a different flue size.
And in any unlined chimney being brought into use.
- Cracked or displaced clay tiles
- After any chimney fire
- When fitting a stove or gas insert
- Unlined chimney being put into service
- Camera inspection is what finds all of it
Types
Stainless steel flexible liner is the common answer for a wood stove or gas insert, sized to the appliance and insulated where required.
Cast-in-place and tile relining exist and suit particular situations. The appliance largely determines what is appropriate.
The camera inspection
A liner cannot be assessed from the top or the firebox alone. A camera survey up the flue is what finds cracked tiles, gaps at joints and previous fire damage.
It is the difference between an inspection and a look, and it is worth asking whether it is included.