How it works

Flue tile is fired from refractory clay to withstand combustion-gas temperatures up to 2000 degrees during a chimney fire. The interior bore is sized to match the firebox opening at roughly 1:10 ratio for proper draft. Tiles are set with a thin bed of refractory mortar and offset from surrounding brick masonry by a small air gap, which allows independent thermal expansion and protects the brick from heat transfer.

Flue tile fails by cracking, spalling, or shifting at the joints. Cracks open during chimney fires when thermal shock exceeds the clay’s tolerance, and shifted tiles expose mortar joints that leak combustion gases into the masonry surround. A CSIA Level 2 inspection">Level 2 inspection uses a video camera to scan every linear foot of flue, and any breach mandates relining with either a stainless steel UL 1777 listed liner or a cast-in-place product.

DFW context

DFW chimneys built before 1990 were universally clay-tile-lined, and many have suffered cracked tiles from the region’s freeze-thaw cycles or from undocumented chimney fires. The Blackland Prairie clay soil’s seasonal movement also shifts tile joints over decades. TSE recommends a video scan as part of any Level 2 inspection on homes older than 25 years, and stainless relining is the standard remediation for tile-lined chimneys with documented breaches.

Related terms

• [UL 1777 listed liner](/glossary/ul-1777-listed-liner/)
• [Refractory mortar](/glossary/refractory-mortar/)
• [Cast-in-place liner](/glossary/cast-in-place-liner/)
• [HeatShield](/glossary/heatshield/)
• [CSIA Level 2 inspection](/glossary/csia-level-2-inspection/)

Sources

• NFPA 211 (2024), Section 10.6
• IRC 2021, Section R1003.11
• ASTM C315 clay flue lining standard