At first glance, it may appear that your gas fireplace is controlled by a 110V wall switch like the rest of the lights in your house. It’s quite possible that the switch on the wall is the same. But upon closer inspection of either the wiring or where it connects back to the gas fireplace you will most likely find that the fireplace switch is actually a low voltage circuit.
So that being said, the Insteon 2450 plug-in module can be used to switch a low voltage circuit. The 2450 will plug in to a wall receptacle, and you will run two wires either to the wall switch location or directly to the wiring controlling the furnace.
Then the 2450 can be controlled by an Insteon Hub or ISY994 Insteon controller, or added to a Vera or Hometroller system by adding an Insteon 2413U interface module to those controllers.