Construct a frame for heat ducts using lengths of lumber that are 2 inches thick by 4 inches wide, a hammer, nails and drywall or plywood. Constructing and installing the frame, or soffit, can take anywhere from one to two days and needs two people in order to complete the project safely.
Measure the heat duct
Measure the length, width and height of the heat duct that the soffit covers. It is best to have the soffit framing extend at least 1 ? inches away from all sides of the heat duct.
Construct the frame
Begin by cutting four pieces of two-by-four to the measured length of the heat duct. These pieces form the box frame for the soffit. If drywall is hung on the soffit to cover the heat duct, then smaller sections of two-by-four need to cut and placed at evenly spaced intervals along the sides of the frame. These two-by-fours support the drywall when it is hung on the soffit. If plywood is used, the smaller sections of two-by-four are not required. Instead, the plywood can be nailed directly to the four long pieces of two-by-four.
Install the frame
Attach the frame to the ceiling or floor studs around the heating duct; these provide the optimum load-bearing support for the soffit. The soffit frame should be attached to these studs using drywall screws that are at least 2 ? inches long. Once the frame is hung, attach drywall to the soffit using the smaller pieces of two-by-four that are positioned at intervals along the sides of the frame.