Mantis Inserts (Bay Window & G-Class)

The Mantis exceeds 90% efficiency– which means it uses about 35 percent less fuel compared to any other vented heater or fireplace system per Btu of heat in your room. This makes Mantis the greenest fireplace you can buy. Because its inexpensive 1 1/2-inch PVC vent pipe can be run inside a conventional 2 X 4 framed wall, the Mantis costs less to install—in materials, time, and labor. The Mantis is the first and only vented fireplace that adds humidity to the dry winter air, making your home feel warmer and more comfortable.


  • Dual Burners – up to 28,000 Btu
  • Exceeds 90% Efficiency – uses 35% less fuel
  • Three-stage heat exchanger
  • Super-Clean burning (reduces emission)
  • Hot-Surface ignition
  • Includes Basic PVC Connections
  • Vents in any direction – up to 40 fett – using regular 1 1/2-inch PVC Pipe
  • Includes Thermostat Remote (FRBTC)
  • Installs as a Direct-Vent or Single-Vent System
  • Humidifies as it Heats


(Actual) Bay Window Front Width35-7/16"
(Actual) Bay Window Height29-3/4"
(Actual) Bay Window Maximum BTU/Hour Input28,000 (natural gas)
(Actual) G-Class Front Width38"
(Actual) G-Class Front Height30-7/8"
(Actual) G-Class Front Maximum BTU/Hour Input28,000 (natural gas)

Efficiency Chart