You can make these frames from strips of metal 4 or 5 inches wide with 1/2 inch or 3/8 inch turned 90 degrees along one edge (Figure 2).
If the return air opening is high on the wall, you need a four-sided frame (Figure 3). The frame shown in Figure 3 will nail in a standard 14 inch stud space. Cut the frame up to the standing edge and then form it into a frame.
Some installers make the cuts as shown in Figure 4 so they have some material from the top and bottom pieces reaching the studs for nailing. Others prefer to make cuts at 90 degrees to the standing edge as shown in Figure 3.
If you have a wide space — for example, you need to put a 14 x 6 frame in a 24 inch on center (OC) stud space and the flanges won‘t reach the studs for nailing — you can extend the frame as shown in Figure 5. On the extensions, fold the standing edge flat as shown in Figure 5.
For a baseboard return air opening, a three-sided frame is required (Figure 6).
Some shops use a plaster stop (Figure 7) for the same application. They are also run out in strips and notched and formed on the job.
Excerpted and reprinted from Top 100 HVAC/R Tips by Leo A. Meyer, one of the books in the Indoor Environment Technician’s Library series published by LAMA Books.
Publication date: 10/7/2013