Direct-vent furnaces are safer and significantly more efficient than conventional furnaces, resulting in less fuel usage and better performance. They are also easier to install in many cases than conventional furnaces, as they do not require a chimney to vent exhaust. Both gas and oil furnaces benefit from direct venting.
Direct-vent furnaces are named for their ability to directly vent exhaust to the outside of a structure through a plastic pipe or other simple vent. This is due to direct-vent furnaces burning their fuel more completely than conventional furnaces, typically by using a secondary combustion chamber to ensure unburned fuel from the initial chamber is burned off as thoroughly as possible. The efficient combustion process produces cooler gases for exhaust. Since a chimney is not required to vent hot exhaust gases, installation of a direct-vent furnace is possible in structures lacking chimneys or other duct systems.
The efficient combustion process of direct-vent furnaces also leads to more efficiency in heating the interiors of structures and lower overall fuel costs. Conventional fuel oil furnaces only achieve average fuel use efficiency ratings of 65 percent, but direct-vent fuel oil furnaces can achieve efficiencies of 85 percent. Some direct-vent propane furnaces are capable of achieving even higher average efficiencies of 95 percent.