Black Hills Inc.’s Simple Guide: How to Install a Window Air Conditioner

Installing a window air conditioner is much simpler than having a central AC system installed. Plus, window ACs are compact, reliable, and durable. Modern units are more energy-efficient as well. Here, we’ll explain how to install a window air conditioner without professional assistance.

Determine Size and Capacity

Window-mounted air conditioners are available in many sizes. They range in capacity from 5,000 British Thermal Units (BTUs) to 25,000 BTUs. Generally, you’ll need 20 BTUs of cooling per square foot (meaning window ACs can accommodate rooms from 150 up to 1,600 square feet).

In a 12- x 16-foot room, which is 192 square feet, a system with about a 4,000 BTU capacity is sufficient. As with central systems, it’s important to select a model that’s not too small or too big. An oversized unit can increase humidity and moisture levels in the room, not to mention consume more electricity.

Prepare the Window

Select a window where the AC will be installed, preferably one with a 3-prong outlet nearby. Most window-mounted units are designed for double-hung windows (if you have a casement or sliding window, you’ll need a unit specially designed for it). To prepare for installation, measure the height and width of the opening, with the lower sash raised. Write down the dimensions when shopping for a properly sized air conditioner.

It’s also important to check for rot or damage around the window frame and make necessary repairs. Next, determine whether to use a support bracket that protects the window sash and sill. Some types don’t require tools to install; others are secured permanently to the window frame. Brackets typically include the hardware needed for installation.

Installing the AC

After preparing the window, wash the glass on the inside and outside. Clear away any clutter you could trip over, and make sure there’s enough space to work. If there’s a screen or storm window, remove it, or fit a spacer block on the windowsill so the unit’s case is not obstructed.

Then proceed with the following steps:

1. Place the box on a stool, then cut the cardboard along the dotted line; this will reveal the AC unit rather than having to lift it out.
2. Read the installation manual and become familiar with the hardware included, such as mounting brackets and window extensions.
3. Raise the lower window sash and center the AC unit on the windowsill; two people should lift and balance it, as an air conditioner is heavy. Be careful not to crush the sharp fins in the back.
4. Keeping a firm grip on the unit, pull down the lower sash until it rests on the AC behind the metal flange on the top of the casing. The AC should tilt slightly outside to allow for drainage.
5. Insert two screws (at a minimum) through the upper flange into the window sash. If the kit includes two L-shaped metal brackets, secure them to the upper sash with screws (using a cordless drill).
6. Extend the accordion-like side panels to close off the openings on either side. Secure them to the window sash track with screws or clips, depending on the model and the instructions.
7. Cut a foam insulating strip or board to the proper length and insert it into any gaps between the AC unit and sash. Weather stripping or foam fillers can be used as well.

Start Using Your Window Air Conditioner

Now, you can plug your AC into its dedicated circuit, using the included plug or a heavy-duty extension cord rated for air conditioners. Turn on the unit and wait for it to start cooling the room. The first time you use the AC, it may take a few minutes for the condenser to kick in and refrigerant to start circulating.

Need Window AC Installation Help? Call Black Hills Inc.

If you’re still unsure how to install a window air conditioner, we can help, whether you’re installing one for the first time or replacing an old system. The process can differ depending on the brand and model. Our trained professionals are familiar with all of them.

It’s very important to install a window AC unit correctly. Our technicians can assist with choosing an efficient system and installing it safely and effectively. For help with AC installation in Olympia, WA, call us at 360-822-9659 today.