Cracked and open flue joints repaired in Lorna Doone

The flue, the liner and why the words get mixed up

The flue is the passage smoke and combustion gases travel through on their way out of the house. The liner is the material that forms the walls of that passage, most often clay tile in a masonry chimney, sometimes a metal or cast-in-place lining added later.

People use the two words for the same thing, and repair offers blur them further. When we write up a flue repair, we name the passage, the lining material and the exact section that is damaged, so you know whether you are paying to fix part of the existing lining or to put in a new one.

Crown cracks and water around the liner

A cracked crown lets rain seep down between the flue tile and the chimney walls. That water can soak the mortar holding the liners and stain the chimney inside the house.

When the crown is part of the problem, we point it out and write crown repair as its own line. Repairing the flue alone would leave the same water path open. Clues include damp patches on the chimney inside the house after rain and dark lines of staining on the tile near the top. Sealing the crack or rebuilding the crown closes the path the water uses.

Tiles that have shifted out of line

When a tile slides out of alignment with the one below it, a ledge forms inside the flue. The ledge catches deposits, disturbs the draft and often leaves an open joint on the other side.

Shifted tiles are usually a sign that the lining has lost support somewhere. We look at how far they have moved and whether a local repair is realistic, or whether the displacement points toward relining. Movement of a single tile at the top can sometimes be corrected when that section is reset. Movement lower down, or across several sections, usually cannot be reached without relining or opening the chimney wall.

What decides the size of a flue repair

No two flue repairs are the same size. The scope depends on the findings, and each factor is spelled out in the estimate.

We explain each factor that applies to your chimney and how it shapes the recommendation.

• How many sections are damaged and where
• How tall the chimney is and how it is reached
• Whether the flue has offsets
• The product or material the repair needs
• Cleaning and preparation before the repair
• Related work at the crown, cap or smoke chamber