How it works

UL 1777 testing subjects candidate liner systems to elevated operating temperatures, simulated chimney fires at temperatures up to 2100 degrees, and post-fire integrity checks. To pass, the liner must contain the fire, prevent heat transfer that would ignite combustibles outside the masonry, and remain serviceable for continued use. Stainless steel grades 304 and 316, aluminum for gas-only applications, and certain ceramic systems all carry UL 1777 listings.

The listing applies to a complete system: liner pipe, top plate, bottom termination, insulation wrap if specified, and connector to the appliance. Substituting components from different manufacturers voids the listing and removes code compliance. Sweeps verify that any installed liner is intact, properly sized, and matches its listed configuration during a CSIA Level 2 inspection">Level 2 inspection.

DFW context

DFW relining work overwhelmingly uses UL 1777 listed stainless systems because the region’s mix of wood-burning, gas-log, and gas-insert appliances spans the full temperature range UL 1777 covers. Insulated 304 stainless is the standard for solid-fuel appliances; uninsulated 316 stainless serves gas inserts. TSE installs only UL 1777 listed assemblies because anything less leaves the homeowner exposed to insurance and code-compliance issues.

Related terms

• [UL 103 HT chimney](/glossary/ul-103-ht-chimney/)
• [Stainless 304 alloy](/glossary/stainless-304-alloy/)
• [Stainless 316 alloy](/glossary/stainless-316-alloy/)
• [Cast-in-place liner](/glossary/cast-in-place-liner/)
• [HeatShield](/glossary/heatshield/)

Sources

• UL 1777 Standard for Chimney Liners
• NFPA 211 (2024), Section 10.6
• IRC 2021, Section R1003.11