Which venting system is most commonly used with a direct vent high efficiency condensing furnace?

A direct vent high efficiency condensing furnace typically employs a Category 4 venting system. This type of venting utilizes both a combustion air intake and a flue gas outlet that are positioned together, often using a coaxial pipe design. Category 4 systems are designed to handle the lower flue gas temperatures that result from the condensing process, which allows for the efficient use of heat and minimizes heat loss.

In a Category 4 venting system, the materials used are often PVC or CPVC, as these materials can handle the condensate produced during the combustion process. The design also allows for venting horizontally through walls or vertically through roofs, providing flexibility in installation.

Categories 1, 2, and 3 venting systems do not typically match the requirements for high efficiency condensing furnaces, as they either are not designed to condense or do not accommodate the lower temperature flue gases that a condensing furnace generates. Hence, the best choice for a direct vent high efficiency condensing furnace is indeed the Category 4 venting system.