How To Make A Return Plenum In Floor Joist

The photo below shows some of the joists in the vented crawl space that the basement was completely connected to.

How to make a return plenum in floor joist.

Inspectors can learn how air leakage from ductwork may cause home energy loss increase utility bills lower comfort levels and make the hvac system less efficient. You rarely construct a plenum i have some who will call a mechanical room with a free return a plenum and that is incorrect. Return air duct is connected together using s slips and drive cleats. See reference 2 for pictures of s slips and drive cleats the return air duct should be installed tight to the bottom of the ceiling joists so it makes a tight seal with the panning.

For example an 8 by 14 inch rectangular duct will fit between 2 by 10 floor joists installed 16 inches apart on center. 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 joist cavity. 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. Secure the duct to the ceiling joists with 1 inch galvanized hanger strap.

Building cavities used as return air plenums is one of the leading causes of duct leakage in homes today. Plan your cold air return ducts to fit comfortably in this area. 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. Corrective measures are also suggested.