How it works

The insert is a fully designed appliance with its own firebox, controls, vent connection, and listing data plate. For gas inserts, a co-linear vent runs two flexible aluminum pipes up the existing masonry flue, connecting at a top plate at the chimney crown. For wood-burning inserts, an insulated stainless steel liner replaces the open-flue connection, channeling combustion gases up a smaller, optimized passage. Pellet inserts use sealed double-wall pellet vent.

Inserts deliver 70 to 80 percent thermal efficiency, compared with 10 to 20 percent for open masonry fireplaces. The trade-off is a smaller view of the fire and a different aesthetic from the original open hearth. Sweeps service inserts annually, cleaning the heat exchanger, inspecting gaskets, verifying vent integrity, and testing CO levels. Properly maintained inserts deliver decades of service.

DFW context

DFW gas inserts are TSE’s most-recommended retrofit for owners of older masonry fireplaces who want efficient heat without abandoning the original hearth. The conversion preserves the brick or stone surround while modernizing the appliance, and direct-vent gas inserts perform reliably in DFW’s mild winters. Wood-burning inserts are less common but appropriate for owners committed to cordwood heating, and pellet inserts serve customers who want automated operation.

Related terms

• [Wood-burning insert](/glossary/wood-burning-insert/)
• [Pellet insert](/glossary/pellet-insert/)
• [Direct-vent gas fireplace](/glossary/direct-vent-gas-fireplace/)
• [Co-linear vent](/glossary/co-linear-vent/)

Sources

• ANSI Z21.88 direct-vent gas appliance standard
• NFPA 211 (2024), Section 11
• UL 1482 wood stove standard