A Vent-Free system uses room air for combustion and delivers 99.9% of the available heat energy directly to the room. Vent-Free systems have an unmatched safety record, thanks in part to their clean-burning technology and their Oxygen Depletion Sensor, which instantly shuts off the valve if oxygen in the room drops to and unsafe level. Because no venting is required, Vent-Free systems offer more installation options.