Return Air Ducts In Wall Cavity

Grossly undersized return air ducts on 2 three ton ac units being replaced with larger ducts to allow proper airflow.

Return air ducts in wall cavity.

These ducts don t pose a fire hazard but will spread flame and smoke in the event of a fire. The original service call was to find. They should be on interior walls across the room from the supply ducts that should be washing exterior walls with conditioned air the red arrow points to a large wall mounted return air vent. These include open floor truss cavities dropped ceilings and air handler platforms.

Building cavity space alone should not be used as a supply or return air pathway. For the cavity to serve as a supply or return air pathway it must contain a sealed insulated duct made of approved duct materials. Corrective measures are also suggested. Aside from wall and floor cavities other framing cavities are also used as plenums or return air ducts.

The duct layout should be considered in the initial framing design stage. Because cavity spaces are leaky building pressure imbalances across the building envelope will occur driving air infiltration into the building. Running a metal cold air return duct between studs requires knowledge of both hvac systems and the components involved in framing. First building codes in many areas require that the cold air return line gets external insulation and therefore you will need to leave a gap for the insulation around the duct return line.

This article addresses the issue of unsealed wall stud cavities or panned floor joists used as a return air plenum resulting in risks such as indoor air quality issues due to negatively pressurized cavities drawing air through cracks along with any contaminants and also condensation by drawing in warm humid air.