How to Install a Window A/C Unit

Window AC Unit

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Project Overview
  • Working Time: 20 - 40 mins
  • Total Time: 20 - 40 mins
  • Skill Level: Beginner
  • Estimated Cost: $140 to $200 for 5,000 BTU units

Sizzling outside temperatures can turn your house into an oven. During summer and other hot periods, your house builds up heat during the day; that heat usually peaks in the late afternoon. Portable fans and ceiling fans are a great help. But when it gets too hot, fans do little more than move the air around. What you need for true comfort is air conditioning. Window A/C units deliver instant relief because they draw warm, moisture-laden air from the room and circulate back dry, cool air.

The most common type of window A/C unit installs in a window that slides up and down. The A/C unit fits in a standard single- or double-hung window opening, with the lower operable sash closing down on the top of the unit. The upper sash remains in place. One or both sides of the A/C unit are then open to the exterior. Most window A/C units include accordion-style panels that fill in that space. If yours is a slider-style or casement window, you will need to purchase a special window A/C unit for your window type.

Before You Begin

Make sure that the window opening is the right size for the A/C unit. For all units, your window's width must be between a minimum and a maximum. If the window is too wide, the side filler panels will not cover it. If the window is too narrow, the A/C unit will not fit. Also, pay attention to height requirements. Even though your window's sash is adjustable, if the A/C unit is too high, it will not fit in the opening. All window A/C units' instructions specify width and height tolerances.

You will need a grounded electrical wall receptacle within the distance of the window A/C unit's power cord. Use of an extension cord is not permitted with many units due to the high power draw; check with your unit's instructions.


Because window A/C units are not just heavy but unwieldy, it is highly recommended that you have a strong assistant to help you. Each of you should be able to lift at least 50 pounds.

What You'll Need

Equipment / Tools

  • Flat-head screwdriver
  • Phillips-head screwdriver
  • Cordless drill with bits
  • Bubble level
  • Pencil
  • Tape measure
  • Scissors or utility knife


  • Window A/C unit


  1. Open the Window and Inspect the Area

    Remove storm windows and window screens. The back of the A/C unit must be free and clear and it must exhaust to the exterior, not to a closed space like a garage. Since window A/C units' backsides drip water as part of their normal operation, make sure there is nothing below the A/C unit that might be damaged by water.

  2. Attach the Top Rail to the A/C Unit

    Window A/C units that fit directly into a window opening will have an L-shaped rail that attaches to the top of the unit. Place the rail on top of the unit and align the holes in the rail with the matching holes in the A/C unit. Attach the rail to the A/C unit using the provided machine screws.


    Be careful not to install the rail backward. The horizontal section of the rail should be pointed toward the exterior.

    Turn the screws by hand, as cordless drills and other power drivers might strip the screws. Use all of the provided screws and make sure that they are driven in tightly since the top rail is an important safety feature.

  3. Attach the Side Filler Panels to the A/C Unit

    With the window A/C unit on the floor, slide each of the side filler panels onto the unit. With the filler panels closed, they should be slightly out of parallel with the vertical front edge of the unit. This is normal since A/C units need to maintain a slight backward pitch for water to drain properly.

  4. Set the A/C Unit in the Window

    Push the filler panels in toward the A/C unit, as close as possible. With assistance, lift the A/C unit from each side and place it on the leading bottom edge of the window frame.

    With one person firmly holding the A/C unit in place, close the window's bottom sash down so that it is behind the A/C unit's top rail. The A/C unit should be sloped backward about 3 or 4 degrees. Use the bubble level to be sure the unit is tilted properly.

  5. Secure the Filler Panels

    Expand the filler panels as far as possible. Attach the filler panels to the window sill using the provided metal frame locks and locking screws. Before driving the screws, create 1/8-inch pilot holes to prevent the window sill from splitting.

  6. Attach the Sash Lock

    Make sure that the window sash is firmly seated against the top of the A/C unit. Screw the L-shaped metal sash lock between the top of the lower sash and the window frame. The sash lock prevents the window from opening.

  7. Insert the Foam Insulation

    Cut the provided strip of window sash seal foam to the width of the window sash. Fit the insulation into the space between the top of the lower sash and the glass on the upper sash.

  8. Make Sure It Works

    Plug the end of the electrical cord into the receptacle and turn on the unit.