Attach a return air grill to a return air duct that ends at what is called a return air boot. Match the boot to the air flow required to heat and cool a home or business. Install the return air boot between wall studs, and screw the grill onto the top. It may be necessary to trim some metal from the edges of duct work so that nothings sticks out from under the grill after installation.
Typically, you install a return air grill or register using screws and a screwdriver or drill. A grill usually has a screw at each corner. If the grill is installed on a hardwood floor, you may need to pre-drill the screw holes to avoid breaking screws. Some return air registers just fit over the return air duct and are held in place by the weight of the grill itself.
Ensure that air grills match the size of their corresponding duct work; for example, a 12-inch duct needs a 12-inch air return cover.
Return air grills typically come in many colors, but you can also paint them before installation. Grills that are placed on ceilings do not need to be as sturdy as those installed on floors where foot traffic is heavy.