Do I Need Dual Wall Exhaust Vents for a Gas Furnace?

Types of Gas Furnaces

• Natural-draft and direct-vent furnaces both receive their required air for combustion from within the home and vent out the chimney. Though high-efficiency furnaces have similar venting requirements and methods to those of direct-vent furnaces, they cool their flue gases further and therefore require a condensation drain. (Reference 1)

How They Vent

• Natural draft furnaces use a single vent to connect to the chimney liner. If you have more than one natural-draft appliance close to the chimney, both can connect with a Y connection to share the chimney liner, requiring no other venting. (Reference 1) Direct-vent furnaces require one approved pipe, such as 636 piping, for the intake and one for the exhaust.

Intake and Venting Confusion

• When you have become accustomed to having a natural-draft appliance, you may wonder why the furnace has two holes. Unlike their natural-draft counterparts, direct-vent furnaces must both receive the air from the outdoors and connect to the outdoors. Therefore, one of the venting slots on the furnace is for air intake, not venting; it only requires only one exhaust vent. (Reference 1)