Access the area holding the return air duct. Work from the attic if possible, or from the room if the top side of the air duct is not accessible.
Unscrew the old return air grille, if present, to remove the screws holding the air grille in place. The screws penetrate either the drywall -- sometimes called sheetrock -- covering the joists where the air duct ends, or the air duct housing, in which case the grille sets down flush with the drywall and connected to the duct itself.
Enlarge or create a new opening, if necessary, first measuring and marking the opening to correspond with the size of hole needed. Slice through the sheetrock with a utility knife to carefully create the opening. Replacing one style of grille for another, for example, may require a larger hole.
Measure the opening again to verify the size. The height and width of the opening must meet the specifications provided with the particular air return grille you use. Shave additional adjustments away until adequate.
Place the return air grille against the ceiling, over the appropriate hole. Drive screws through the holes provided in the air grille cover into the duct housing, if present, or into the joists surrounding the hole. Tighten the screws firmly, but do not over-tighten to avoid digging your frame into the drywall, damaging it.
Things You Will Need
- Utility knife
- Tape measure
- An air return duct by definition must use either the space between the joists or a distinct duct to transfer air. Therefore, the air return opening should have wood completely framing the opening, under the drywall. If you find a lack of wood to attach the grille to, cut 2-by-4 inch boards to fit the space involved and nail between the ceiling joists to secure. If done from the upper side, you don't even have to disturb the sheetrock; if you have to do so from the bottom, you will have to cut a much larger opening. Mark the dimensions for the new grille on the replacement sheetrock before securing in place. Attach the grille to the sheetrock, piercing the wood behind, as normal to install.