How to Install a Window Air Conditioner

Add a little cold comfort where you need it most by safely installing a window air conditioner sized to suit your needs. We have step-by-step instructions and helpful DIY tips to guide you through your window air conditioner installation.

• Determine the window where you’ll install your air conditioner. If there’s no three-prong outlet nearby, you’ll need an extension cord labelled for air conditioner use.

• Check the load on the circuit you plan to use. If it’s also powering other devices, even simple ones such as a hair dryer, you may want to choose another window near a different circuit, add a dedicated circuit or move those other appliances somewhere else to avoid a tripped breaker or blown fuse.

• Not every air conditioner fits every type of window. Determine whether your window is a slider, a double-hung, or a casement style. Most units work only in double-hung windows with a lower sash you can raise and lower. Also, measure the width and the height of the window opening to confirm whether an air conditioner will fit.

• Decide how much additional insulation and rain protection you’ll want to add around the window (beyond the air conditioner’s side curtains). For example, you may want to add pieces of white expanded foam insulation along the sides or within the gap between the upper and lower window sashes.

• How’s the weather outside the window? A west-facing window could catch enough sun to force the air conditioner to work harder. Does the wind typically whip rain against that side of the house? Consider adding additional barriers to keep the water outside.

• If you have curtains or drapes at the window, consider adding a blind or shade. These options won’t block the air conditioner and can be adjusted to give you privacy.

Inspect the window to make sure it’s in good repair. After installation, you probably won’t open that window for months until it’s time to remove the unit, so now’s a good time to wash the glass inside and out. You’ll also want to clear the area around the window and leave yourself plenty of working space with no tripping hazards.

Check for obstructions in the window opening, such as storm window frames or screens that might interfere with the overhanging part of the air conditioner on the outside. Raise or remove the screen and either remove the storm window (and frame) or fasten a spacer block to the windowsill to lift the air conditioner case away from the storm window frame.

Note: There’s a reason to fasten spacers in place instead of leaving them loose. Weather, vibration and the challenge of lifting a heavy air conditioner onto a windowsill can knock an unsecured spacer out of position, allowing the unit to tilt or even fall.

Remember to: 

Follow the manufacturer’s instructions to prepare the air conditioner for mounting. This may include attaching brackets and the accordion-style side curtains, for example. Double-check the air conditioner’s measurements and compare them to the window opening.