How to Fit an Air Conditioner in a Basement Window

An air conditioner on a white background.
  • 2-3 hours
  • Beginner
  • 30-60
What You'll Need
Plywood or styrofoam

When you need to install a window air conditioner in a basement window, it can often be a struggle to get the air conditioner to fit and rest securely in the window. Basement windows are commonly not as uniform as other home windows. This can be a problem when trying to install a standard size window air conditioner. Here are some tips that can help you when you install the air conditioner.

Step 1 - Seal Air Leaks

When installing an air conditioning unit in a basement window, you will oftentimes have to remove window bars and even the window entirely to fit the unit securely. Removing the window will in most cases present a new problem of air leaks as small as a crack to several inches, depending on the size of your window frame.

If there is a bit of space between the window frame and your unit, there are several possible solutions. You can place boards under the unit so that it is resting on the outer sill. Tilt the air conditioner slightly so that it drains properly outside and prevents rust from forming. Another option is to fill the gaps on the side or top with Styrofoam or plywood.

Step 2 - Secure the Air Conditioner

The most important thing about basement air conditioners is that they must be securely in place. That is often the most difficult part about a window unit. If you will be shopping for a new unit, take measurements of your window before you go to the store.

New or used, you may need to make a small shelf for the air conditioner to rest. The shelf should have a slight slope as well so that the air conditioner drains outside. Even with a shelf, you may still have openings around the window. If that is the case, seal them with a small board taped into place. If you have a sliding window, use tape to create a seal along the sliding portion so that you can still open the window if you want.

Step 3 - Secure Your Home

Once you install a window air conditioner unit, your window lock will no longer function properly. To maintain security in your home, cut a board or stick the length necessary to fit between the upper window frame and the top of the sash. Doing so will prevent unwanted intruders from prying the window open and entering your home.

Using these simple tips, you can easily install your air conditioning unit and have it working to its full efficiency this summer. Be sure to thoroughly seal all of the leaks, and you will be on your way to a cool and energy efficient summer.