How to Install a Window Air Conditioner and Keep It Level

What a solid install comes down to

You've got the unit in the room and a window picked out, and most of the real work happens before it leaves the floor. We'd settle the window fit and how the unit will be supported before fitting a single screw, because opening sizes differ from model to model and the mounting has to carry the whole air conditioner.

Tilt is the other half. GE wants the unit sitting level or tipped slightly toward the outside, while the installation tip sheet calls for a slight tilt so water drains, without overtilting. We'd aim for a gentle outward lean, which fits both, and follow your own model's instructions wherever they differ.

Is your window right for this method?

Window units are built for standard single-hung or double-hung windows in wood or vinyl frames. If your sill is a different type, your unit's installation instructions take over from here.

Windows that slide side to side and casement windows that swing outward aren't options for a conventional window unit like this.

Measure the opening's height and width, then compare them with the minimum and maximum window dimensions in your model's installation instructions. Different models need different openings, so one model's numbers won't tell you about another's.

If anything about your model or your window still raises questions at this point, stop and consider hiring a professional to help before the unit goes near the sill. Tell them the model and the window type, since those are what the fit depends on.

Sort these out while the unit's on the floor

Run through these before lifting anything, because each one decides whether this window can take the unit at all.

Open the window as far as it goes, take out the screen and clean the sill, glass and frame. If you think you'll need extra foam to fill space around the unit, have it ready now.

For tools, gather a tape measure, pencil, scissors, a level and the screwdriver your hardware calls for. On GE units you'll also want a drill with a 1/8-inch bit for the pilot holes.

Plan how the unit will be held up. It needs support from underneath or firm fastening from inside with angles, and metal brackets or mounting rails can do that job. Anything carrying weight has to be fastened to the building's structure and be strong enough for the unit's size and weight.

Fitting the rail, seals and side curtains

These steps fit GE units with a top rail and slide-in side curtains. Panel hardware varies, since some panels screw on and others slide into place, so match each step to the parts in your box. Keep GE's installation steps (opens in a new tab) open if your unit is a GE.

1. Screw the top mounting rail on with the Type-A screws that came with the unit, three or four depending on the model.
2. Stick weatherstripping along the top and bottom edges of the window, trimming it so it fits your window's size.
3. Add weatherstripping to each side of the curtain frames that reach from the unit to the window sides, so those edges seal once it's in.
4. Slide a side curtain panel into the rails on each side of the air conditioner.
5. With the panels in, fit the curtain frames by their left and right markings, sliding each one into the top slot of the bottom rail.
6. Snap the side curtains into the frames, so each side has its panel and frame together.

Those panels and strips are what keep cool air in and hot air out, so get them snug before the lift.

Lifting it in and getting it level

Measure the window from side to side and mark the center point, so you have a target before anyone's holding the unit.

1. With your helper, lift the air conditioner and set it into the window.
2. Slide it until the front edge of the bottom mounting rail sits against the back edge of the windowsill, with the unit centered on your mark.
3. Lower the window so the front edge of the top mounting rail ends up in front of the window.
4. Set your level on the unit and check that it sits level or leans slightly toward the outside.

If the reading is off, fix it now, before anything is screwed down, because the curtains and side brackets get fastened next. A slight outward tilt lets water drain, so lean it just enough and stop short of overtilting.

Screwing the curtains and brackets down

This is where the unit goes from resting in the window to being held there. A poorly installed unit can fall out and hurt someone, or damage the window badly enough that it needs repair or replacement.

1. Pull the curtain panels out until they fill the window area on each side of the unit.
2. Drill pilot holes with the 1/8-inch bit and drive the four Type-B screws in, so the side panels are held in place.
3. Loosen the screw near the bottom on the right side of the unit, slide a side bracket over it so the bracket rests on the sill, then tighten the screw.
4. Drill pilot holes through the holes in the bracket with the 1/8-inch bit and attach it to the sill with two of the four Type-B screws.
5. Repeat the bracket on the left side, so both sides are fastened to the sill.

If the side panels still leave gaps to the window frame, fill them with the extra foam you set aside.

Locking the sash so the unit stays put

Either the unit has to stay in place when the window is opened, or the window gets fixed so nobody opens it by accident. The closed window bearing on the mounting rails helps hold the unit, and on GE units a lock bracket on the sash finishes the job.

Install the window lock bracket to the window and frame, above the lower window. On a wood window the hole faces you, and on a vinyl window it faces to the side. Drill a pilot hole and fix the bracket with one Type-B screw.

Seal the top by cutting the foam top window gasket to your window's width and pushing it in between the glass and the window. That closes the crack against outside air and insects.

Keep the top of the unit clear from now on. Plants, antennas, satellite dishes and anything else stay off it.

Keeping it level and secure all season

Vibration from the unit, wind and weather can all work on an install over time, so check the air conditioner's position and the condition of the window frame every so often to make sure it's still supported and secure.

When you check, put the level back on the unit and look for the same level or slight outward lean you set at the start, shims that are still fastened, and a frame that's still in good shape.