A gas furnace vent pipe is used to remove toxic gases that are created during the combustion process and release them outside of the building or house. An improperly vented gas furnace can pose a health hazard as it can emit harmful gases into the air inside the building.
As of 2015, there are several types of gas vents that can be installed on a furnace. Older gas furnace models typically use a direct vent that emits the byproduct of combustion directly outside. More modern furnaces can use type B piping, which is more environmentally friendly and is generally covered by insurance companies.