Keep Ducts in Conditioned Space

• Design the HVAC (as well as affected framing and building assemblies) to locate all ducts within conditioned space. If all ducts cannot be located within conditioned space, ensure that most of them are located within this space.

Keeping all supply and return ductwork within conditioned space assures that any air leakage that does occur won’t be lost to the outdoors. This design strategy can also help avoid durability issues such as the formation of condensation on the outside of cooling ducts located in humid spaces like an attic or crawl space. With repeated exposure to moisture, nearby framing or drywall can be damaged and harbor mold growth.

On the space heating side, supply ducts located in the attic can contribute to the formation of ice dams—especially if the ductwork is leaky as well. In addition to impacting the durability of a home, ducts in unconditioned space combined with poor duct sealing can compromise indoor air quality. Contaminants can be pulled into return ductwork and subsequently distributed throughout the home.