An unvented gas stove is a space heater that has no chimney or flue and is located in the room it heats. These devices use natural gas or propane as fuel to produce heat.
Because they do not require a vent, these heaters are easy to install. They are available as freestanding or wall-mounted units. Small units work well in heating a single room, but larger units that include a blower to distribute heat to several rooms are also available. Manufacturers also offer vent-free fireplaces that burn the same fuels. Some of these fireplaces mount directly on the wall, offering the ambiance of a fireplace at a much lower cost. Units range in sizes from 5,000 British thermal units per hour to 38,000 Btu per hour.
Unvented gas stoves cause some concern about indoor air quality when they are in operation. They are illegal for use in California. Federal regulations require that these stoves have oxygen-sensing safety devices. If oxygen levels become too low in the room, the device automatically extinguishes the flame. Other concerns include carbon monoxide, water vapor, nitrous oxide and carbon dioxide. Carbon monoxide and nitrous oxide are poisonous gases. Carbon monoxide and water vapor are not poisonous but have the potential to cause other issues.