Only works with ventless product, not with direct vent sealed glass units. 14D0467 Monessen Hearth Replacement SIT 820 NOVA Vent Free Fireplace Natural Gas Valve Model 0820637. This is a millivolt valve. Uses a thermopile (main valve), and thermocouple (pilot). Has 3/8" female pipe thread inlet and outlet connections. You can vary hi - lo flame height. Millivolt valves can be controlled by a switch, remote control, or thermostat. This is used by Monessen, Majestic, Empire, and many other fireplace companies. There are many versions of these valves with different thermocouple threads. Make sure you match your model number.