Secure the duct to the ceiling joists with 1 inch galvanized hanger strap.
How to make a return plenum in floor joist.
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.
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.
For example an 8 by 14 inch rectangular duct will fit between 2 by 10 floor joists installed 16 inches apart on center.
Did that cause problems.
Return air duct is connected together using s slips and drive cleats.
Building cavities used as return air plenums is one of the leading causes of duct leakage in homes today.
The photo below shows some of the joists in the vented crawl space that the basement was completely connected to.
An enclosed portion of the building structure other than an occupiable space being conditioned that is designed to allow air movement and thereby serve as part of an air distribution system.
Corrective measures are also suggested.
You rarely construct a plenum i have some who will call a mechanical room with a free return a plenum and that is incorrect.
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.