AC Unit Wall Opening Installation

Measure the height and width of your AC unit with the tape measure.

Read through the AC installation instructions provided by the manufacturer to determine what additional framing is required for the installation of the unit. Add the framing dimensions to those of the AC unit to determine the amount of space required for the frame and unit both.

Run a stud finder over your wall where you wish to place the AC unit. Choose a location for the AC unit that's easily reached, towards the base of your wall to simplify the installation process. Pick a space beneath a window to avoid needing to reinforce the opening in the load-bearing wall. Windows already have headers above them that takes the load from the wall section off the wall studs. You’ll want to find a location that requires the least number of studs to be removed from the wall cavity to fit the unit and frame. Mark a square on your wall where you intend to place the unit and frame using a straightedge and pencil.

Turn off the electricity for the wall outlets and fixtures from the circuit box for your home to avoid any mishaps from cutting through wires. If the stud finder indicates the locations of pipes through the wall it's best to find an alternate opening rather than reroute the plumbing running through that particular wall section.

Put on a pair of work gloves, safety goggles and a dust mask. Cut through interior drywall with a utility knife along the marked line to reach the cavity interior. If your interior wall is plaster, then use a hammer and chisel to cut through the plaster coating along the marked line to the wood slats beneath. Cut through the slats with a circular saw, taking care not to cut through the wall studs in the cavity. Pry off the slats from the studs with a pry bar.

Cut through and remove any insulation present in the wall cavity within the area of the frame with the utility knife.

Remove any wall studs located withing the framing area with a reciprocating saw. This will leave a line of studs hanging free both above and below the frame area. If there is wiring running through the area, then reroute the wiring either above or below the opening through the partial studs. Cut notches in the studs with the saw to place the wiring into.

Build the required framing for the AC unit between the wall studs with 2-by-4-inch lumber, to support the weight of the AC unit and to cap the ends of the cut studs. Make certain your frame includes cross bars placed between the studs framing the opening, both at the base and top of the opening, as well as planks to the sides of the opening between the cross bars. Make the framed opening 1/2-inch higher and longer than the space needed, to create space for shimming the AC unit in place.

Cut the framing lumber with a circular saw, and nail the frame into place using 10d nails. Make the cross bars long enough to run the full width of the cavity between the wall studs adjacent to the opening. Place the cross bars along the top and bottom of the opening. Nail them in place by driving the nails through the cross bars and into the cut ends of the wall studs, then drive nails through the full studs adjoining the opening space into the sides of the cross bars. Place the side bars running vertically along the sides of the AC opening between the cross bars and nail them into place by driving the nails through the cross bars and into the side bar ends.

Drill holes through the wood sheathing and exterior wall covering at the corners of the frame to transfer the frame location to the outside wall.

Locate the holes drilled at the corners of the frame to the outside. Mark the opening with a straightedge and pencil onto the covering material. Cut through any covering siding or veneer along the marked line using a circular saw with a blade attached that’s appropriate for use with the siding material.

Cut through the wood sheathing along the interior of the frame line with the circular saw to complete the opening.