Using Floor Joist For Cold Air Return

The space between the floor joists may be used as part of the return duct system.

Using floor joist for cold air return.

Panned floor joist are a commonly utilized as return ducts by nailing gypsum board foil insulation osb flooring panels or sheet metal to the joists. This is an appropriate use for space that cannot be used for actual heating and air conditioning. John here using the joists as a return is common practice if it is inside the envelope conditioned space. All the duct work for heat uses 5 and 6 inch pipes which is fine and makes no noise.

Hallways as part of a return air system. Corrective measures are also suggested. Using floor joists as return ducts by panning can cause leakage because negative pressure in the cavity will draw air from the outside into the cavity through the construction joints of the rim area at the end of the joist cavity. As a result this panned joist return duct sucked in a lot of air from this basement when the furnace or air conditioner were running.

These sheets of metal make constant noise when we walk on the floor above the return duct. Still commonly used is the panned floor joist. I have a new house and have a question. It is impossible to create an airtight seal with this method and together with the negative pressure that is created inside the cavity air leakage occurs through joints of the rim at the end of.

The photo below shows some of the joists in the vented crawl space that the basement was completely connected to. Did that cause problems. Most prefer rigid to flex since flex creates too much resistance and decreases airflow. All my cold air returns use the space between the joists with sheet metal screwed against the joists.

Plan your cold air return ducts to fit comfortably in this area. Homes with basements often use wall studs and floor joist spaces as return air cavities. 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.