Images of direct-vent wall furnaces are available through Home Depot and Rinnai. Clearance AC provides an image and a diagram of how these units heat a room without using room air for combustion. These furnaces release exhaust to the outside and take in fresh air for combustion.
Direct-vent wall furnaces have a heat exchanger like central heating systems. This firebox prevents the mixing of room air with the fuel for combustion. The furnace heats room air as it circulates around the heat exchanger. Manufacturers include a piezoelectric starter for the pilot light, and the units depend on a thermostat to regulate the temperature in the room. An optional blower helps to provide more even heat distribution, but the units continue heating even with a power outage. Direct-vent furnaces are available in sizes to heat a single room or an entire home.
Direct-vent wall furnaces use a double-walled vent to provide both fresh air and exhaust fumes from a single hole. Exhaust fumes exit through the center opening of the vent, while fresh air enters through the opening between the metal walls. The installer places this vent directly behind the stove through an outside wall, eliminating the need for a flue or chimney.