Vent-Free A Vent-Free system uses room air for combustion and delivers 99.9% of the available heat energy directly to the room. VF systems have an unmatched safety record, thanks in part to their clean-burning technology and their Oxygen Depletion Sensor, which instantly shuts of the valve if oxygen in the room drops to and unsafe level. Because no venting is required, VF systems offer more installation options. VF systems are limited to 40,000 Btu and must be operated as supplemental heating sources in conjunction with a central furnace that circulates air Advantages: Unmatched efficiency – 99.9% Offers the most installation versatility Usually less expensive to buy and to install Can operate with a remote or thermostat Most systems can provide live-saving heat during a winter power outage Choose fireplace, insert, heater, cast iron stove, burner and log set, or contemporary burner