What the liner does
A chimney is a masonry shaft. The liner is the smooth, sealed passage inside it that the smoke and combustion gases actually travel through. It does three jobs: it keeps the heat of the flue gases away from the brick and the wood framing around the chimney; it keeps carbon monoxide from seeping through cracks in the masonry into the house; and it gives the gases a smooth, correctly sized path so the fireplace draws properly.
Without a liner, or with a damaged one, the masonry takes the heat and the acids in the smoke directly. Mortar joints erode from the inside, and a chimney fire — creosote in the flue igniting — can reach the framing.
The three kinds of liner
- Clay tile. Square or rectangular terracotta sections, stacked and mortared, built into the chimney when the house was built. Standard in Toronto houses from roughly the 1920s on. Cheap and durable when intact, but the joints between tiles open up over time, and tiles crack from heat and from water freezing in them.
- Stainless steel. A flexible or rigid stainless pipe, run down the existing chimney and sealed at top and bottom, usually with insulation around it. This is the standard fix for a cracked clay liner or an unlined chimney, and the standard way to connect a wood stove or insert.
- Cast-in-place. A cement-like lining poured around a form inside the chimney, creating a new smooth flue. Used when the chimney is unusually shaped or structurally weak; less common.
Signs your liner is damaged or missing
- Pieces of clay tile in the firebox or on the smoke shelf.
- A chimney built before about 1950 with no visible tile at the top of the flue.
- Mortar joints on the outside of the chimney that are eroding from the inside out, or a chimney that is warm to the touch on the outside during a fire.
- A smoky fireplace that never drew well — often a flue that is the wrong size for the fireplace opening.
- A home inspection, WETT inspection or insurance report that says "flue tiles cracked" or "unlined".
Most of these can only be confirmed with a camera. The free inspection runs a camera the length of the flue and gives you the photos — a crack in a tile at the third floor is not something anyone can see from the fireplace.
Why old Toronto chimneys so often need one
Three reasons come up again and again on the chimneys we inspect. Houses from before the war were often built with no liner at all — bare brick on the inside. Houses from the 1950s to 1980s have clay liners whose joints were mortared with the same mortar as the brick, which the acids in wood smoke eat away. And decades of Toronto freeze-thaw, on a flue with no cap, crack the tiles from the top down.
A stainless liner solves all three at once: it is a continuous, sealed pipe inside the old masonry, and it does not care what the brick around it looks like.
What a liner job involves
The flue is swept and inspected with the camera. The liner is sized to the appliance — a fireplace, a stove or an insert each need a different diameter — and run down from the top of the chimney, insulated, and connected at the bottom. A new top plate and cap seal it at the crown. On most houses it is a one-day job, done from the roof and the fireplace, with no opening of walls.
What it costs depends on the height of the chimney, the diameter, and whether the flue has offsets. You get the price in writing after the camera inspection, before anything is ordered. See chimney liners.
