Which type of gas furnace uses a venting system that requires two pipes, one for exhaust and one for intake?

The correct answer is Category IV furnaces, which utilize a two-pipe venting system comprising one pipe for exhaust and another for intake. This design is specifically engineered for high-efficiency gas furnaces that operate with condensing technology.

In a Category IV system, the combustion air is drawn from outside the home through one pipe, while the byproducts of combustion are expelled outside through a separate vent pipe. This dual-pipe configuration enhances efficiency and safety, as it minimizes the risk of backdraft and allows the furnace to take advantage of the higher density of cool outside air for combustion, thus optimizing performance.

Understanding this venting configuration is crucial for installation and maintenance practices, as it not only dictates how the furnace operates but also contributes to overall safety and efficiency standards in HVAC systems. This is in contrast to other categories, which may employ different venting methods that do not require a separated intake and exhaust system.