It's normal to be nervous about a window air conditioner falling out. It could be catastrophic, and they do seem awfully precarious, especially when you think about how the majority of the unit hangs out of the open window. In reality, a window air conditioner should be perfectly safe as long as it's properly installed. Take all the possible safety measures and your air conditioner should stay put until you're ready to remove it from the window.
A properly installed and secured window air conditioner won't fall out of a window.
Select the Proper Window
It's highly unlikely that your air conditioner will fall out of a window unless you make one of two mistakes: choosing a unit that doesn't fit the window and failing to secure the unit in place.
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So before doing anything else, make sure that your window is appropriate for the AC you've chosen. Obviously, the window opening needs to be larger than the air conditioner, and it should be double-hung with a bottom pane that slides up. A standard air conditioner won't fit securely in a window that opens side-to-side or opens out.
Follow Installation Instructions
The other essential step for a safe installation is reviewing the manufacturer's instructions. Find them online if you don't have the original packaging. Different models have different safety features, and the stakes here are high enough that you definitely don't want to take any chances while installing the unit.
This is especially important if you're installing a new air conditioner right out of the box, as you may need to install mounting rails and side panels to the AC before doing anything else. These parts create a frame around the unit that help it lock securely into place in the window. Grab a screwdriver before you get started.
Window Air Conditioner Safety Accessories
Installing a metal safety bracket on the outside of your window will give your air conditioner support. In turn, you'll have peace of mind that the AC won't come tumbling down on someone's head.
These brackets are sold separately and are rated by weight, so you can buy one that supports your air conditioner no matter its size. Installing the bracket is often as easy as drilling a few screws through the bracket into the sill. If you live in a rental, you may want to check with your landlord before installing brackets or a window AC.
Once the safety bracket is installed, consider putting some strips of weather-sealing foam into the sides and bottom of the open window frame. This product will fill any gaps to help keep hot air, rain and insects from getting into the room, and it will keep cold air from escaping.
Safely Install Window Air Conditioner
Finally, you're ready to install the unit. Always have a second person to help move the air conditioner into place and hold the unit steady while you secure it. Position the AC's lower mounting rails against the edge of the window sill. When you slide down the window, the sash should fit just behind the AC's top mounting rail. Slide the side panels out to completely close any gaps.
Depending on your model's specific instructions, use screws to secure the side panels to the window frame and/or to secure the top mounting rail to the window sash. Your AC may also come with small metal brackets that need to be screwed into place for additional security.