Installing a Window Air Conditioner

If you don't have central air conditioning, you may find yourself lingering in front of the refrigerator this summer - unless you install at least one room air conditioning unit, preferably in the bedroom. There are many installation options for an individual room unit, but the basic choice is between a removable unit installed in a window or a permanent one built into a wall. A window unit is easier to install. You don't have to make a hole in your wall and most units can be plugged in and working an hour after you open the box.

The best location is a double-hung window near a wall outlet with sufficient capacity to handle the appliance. The weight of the unit is carried on the sill and held in position with brackets at a slight downward slope for proper drainage of condensation. Extensions on each side of the unit slide out to seal the opening. Before buying the air conditioner take accurate measurements of the window and buy one that will fit within these measurements. If the window also has storm windows, consider the opening of that frame and make sure the unit will fit these measurements as well. The cooling capacity of an air conditioner is given in British thermal units (Btus). As for determining the cooling power that you will need for the room, the most general rule of thumb would be to buy one ton of cooling (12,000 Btus) per 500 square feet of floor space. If the room has a southern exposure, you may want a more powerful unit than determined by just the room measurements.
Project Basics


Estimated Project Time:
1 hour

Start Tips:
Plan to install the air conditioner near an outlet that can handle the electrical needs of the unit

Safety Tips:
Make sure the air conditioner and its mounting brackets are fastened properly and securely to the window


Tools and Materials:

Window air conditioner unit, including mounting and installation hardware
Measuring tape
Spirit level

Screwdriver or power drill/driver
Foam strip, as needed
Waterproof caulk
Caulking gun


Fig. 1

1) Install the Mounting Hardware
Older units (and some very large machines) rest on external brackets, but modern air conditioners rest on sill-mounted supports. Open the window and install these fittings properly, using the hardware and following the instructions that accompany the unit. If you install the mounts improperly, the air conditioner may fall from the window when you raise the sash, damaging the unit and whatever happens to be underneath it. If the wood of your sill seems soft and partly rotten, use another window or replace the sill. Carefully mark the placement of the fittings. (Fig. 1)

Fig. 2

One end of this bracket is screwed to the sill. You adjust a center screw to level the unit and provide condensation drainage. (Fig. 2) If your window frame is metal instead of wood, use sheet-metal screws to install the brackets.

Fig. 3

2) Set the Unit in Place
Open the window wider than needed to receive the air conditioner and then follow the instructions that accompany the air conditioner to set it in place. If the unit is heavy, have someone assist you in lifting it.

This self-contained AC unit has integral handles that make it easier to lift it onto the sill and over the mounting bracket. (Fig. 3)

Fig. 4

And then as you slide this machine into the window opening, a pocket underneath locks in place over the bracket. (Fig. 4)

Fig. 5

3) Fit the Extensions
Close the window onto the air conditioner and pull out the extensions on both sides of the unit, closing up the openings between the unit and the sides of the window. When the extensions are snug against the window, fasten each to the sash. (Fig. 5)

Fig. 6

4) Secure Window Sashes
Using the angle bracket provided with most machines, secure the two window sashes to each other over the air conditioning unit. (Fig. 6)

Fig. 7

5) Finish the Installation
To seal the installation inside, use a foam strip (provided with most machines) to fill the air gap where the sashes overlap. (Fig. 7)

Caulk the unit outside, check the manufacturer's instructions for operation and maintenance, and plug in the unit.