Cracked and open flue joints repaired in Windhover

The kinds of lining the code accepts

For ordinary residential appliances, Section R1003.11.1 of the Florida residential code lists four acceptable flue lining systems. Any repair or replacement we propose has to leave your flue inside one of them.

When a proposed fix does not clearly land in one of these categories, we say so and explain what that means for using the fireplace.

• Clay flue lining complying with ASTM C315
• Listed and labeled chimney lining systems complying with UL 1777
• Factory-built chimneys, or chimney units, carrying a listing for use inside a masonry chimney
• Other approved materials that hold up against flue gases and condensate to 1,800 degrees F without corroding, eroding, softening or cracking

The space around the tiles

Clay flue liners are installed with an airspace or insulation separating them from the inside face of the chimney walls, not exceeding the thickness of the liner, according to Section R1003.12. That space lets the lining heat and expand without pushing directly on the masonry.

Repairs that fill this gap carelessly can transfer heat and stress to the brick. We keep repairs within the lining itself unless a different scope is agreed, and we explain how the method we propose treats that space.

One flue for one appliance

BIA Technical Note 19B notes that many building codes do not allow flues of dissimilar systems or fuels, such as an appliance and a fireplace, to be combined, and that separate flues are the normal approach.

When an old conversion has tied two appliances into one flue, or an appliance has been vented into a fireplace flue, repairing the tile alone does not settle the question. We point out the arrangement, explain the concern and write up the repair scope around it.

Why flue damage matters to the framing nearby

The Florida residential code, in Section R1003.18, requires an air gap of 2 inches or more between combustibles and a masonry chimney located indoors or within an exterior wall, and 1 inch or more for a chimney standing wholly outside.

Those clearances assume the flue lining is doing its job. When tiles crack or joints open, more heat reaches the chimney masonry than it was built for. That is one reason we treat liner damage as a safety matter, not a cosmetic one.