A wall air conditioner, though similar in size to a window air conditioner, is often a better option. For one thing, you are not required to remove and store it during cold weather as you would a window unit. Here are the materials and tools you'll need to install a wall-mounted air conditioner in 6 steps.
Step 1 – Choosing a Space on a Wall
Using a stud finder, locate a space on one of your walls where you will cut an opening for your unit. Use the stud finder to warn you of electrical wiring that might be in the wall where you plan to make your opening.
Step 2 – Draw Lines of Your Opening
Use your level to draw a line for the top edge of the opening. Then draw 3 more lines that will complete a rectangle 2 inches bigger on each side than the air conditioning unit. Be sure that in marking the edges of the opening you use your level to make the horizontal lines level and the vertical lines plumb.
Step 3 - Cut out Your Drywall Opening
Cut through the drywall along the lines you've drawn, using a drywall handsaw. Next, cut out a piece of the insulation and save it for future use.
Step 4 - Cut out Your Exterior Siding Opening
Using your level and pencil, mark a rectangle on the exterior siding, the same size as the drywall opening. Be sure to make it level and plumb. Then, with your drill and wood bit, drill a hole through the exterior siding and inside the rectangle you've drawn. This drilled hole should be big enough to insert the blade of your reciprocating saw into. Next, use your reciprocating saw to cut out an exterior siding rectangle, finishing the opening in the wall. Cut a piece out of the wall stud you find in the opening. Make the opening big enough that you will be able to slip your air conditioner into the opening.
Step 5 – Frame Your Opening
Make a rectangular frame out of a 2" X 4," one that will fit snugly into the wall opening. Slip the unit into place and secure it to the wall studs by driving nails through it and into adjoining wall studs.
Step 6 – Insert Your Air Conditioner
Place your air conditioner into the wall opening. On each of the top and bottom edges of the unit, or on the two side edges, you'll find a metal or plastic flange (rim) with screw holes. Once your air conditioner is in place, drill a screw through the flange hole and into a stud or the 2"X4" frame. This will hold the unit firmly in place. Place the saved insulation into spaces between the unit and the wall, then add drywall to close the opening, and your job is done.