Project Guide

How To Install A Window Air Conditioner

Prepare Window and AC Unit
A person securing a support bracket to install a window air conditioner.

Before learning how to install a window air conditioner, be sure that your window is sound and sturdy enough to support the weight of the air conditioning unit. If there’s any rot or damage around the window frame, make the necessary repairs first. 

Something else to consider when deciding how to install a window AC unit is whether to use a support bracket. This type of bracket is sold separately and is recommended because it transfers some weight of the air conditioner from the window sash and sill. It provides additional safety and minimizes the chance of damage to the window, window parts or the outside wall.

Some bracket models require no tools and can be easily removed for seasonal storage. Other types of support brackets attach to the window frame for a more permanent solution. Follow the manufacturer’s instructions for how to install a window air conditioner support bracket. Open the lower window sash and attach the bracket using the provided hardware, if necessary. Then:

  • Slide the accordion panels onto both sides of the air conditioner, if not pre-assembled in a guide track.
  • Installing a window AC unit is usually a two-person job, so carefully lift the air conditioner with a helper and place it through the open window.
  • Rest the unit on the bottom of the window frame and mounting support bracket.
  • Center the air conditioner in the window opening and position the unit’s bottom guide, or flange, flush against the window stool. 
Place and Secure Air Conditioner
Two people lifting an air conditioner to install it in a window.

Always follow the manufacturer’s instructions for how to install a window AC unit, because some types might have steps specific to that model. Keep your helper nearby to assist with balancing the heavy unit in the open window until it is secure.

  • Once the air conditioner is resting on the window frame, pull the upper window sash down to the top of the box and behind the upper flange to provide additional stability.
  • Following the enclosed directions for how to install a window air conditioner, use screws to attach the cabinet and/or flange guide to the window sash and window stool at the top and the bottom of the unit.
  • Use a screw or screws to attach an L-shaped window locking bracket to the upper window sash to prevent the lower sash from accidently being opened. Use a power drill to make a pilot hole for the screw and tighten the bracket using a screwdriver.
Fasten Side Panels
A person extending an AC unit's side panel while installing a window air conditioner.

Once the window air conditioner is secure, take some final steps to help keep the warm air outside and the cool air inside.

  • Extend the accordion panels from both sides of the air conditioner to the window sash track.
  • Secure the side panels with screws.
  • Window air conditioners often come with a foam insulating strip. Cut the strip of foam to the correct length and insert it between the upper window sash and the lower window sash.
  • If your model does not have a foam strip included, purchase non-adhesive foam stripping and use it to fill the gap between the window sashes. 
  • Review the maunfacturer's instructions for how to install a winddow AC unit to ensure all included installation hardware was used.
  • Finally, plug the air conditioner into an outlet and turn on the unit.

Installing a window AC unit is a gratifying project. It requires a small amount of heavy lifting with the assistance of a helper and tightening enough screws to secure the unit, but the result is a cool room to enjoy during the warm season. Many window air conditioners can also provide heating for a chilly room, which means learning how to install a window air conditioner has year-round benefits.

During installation, use a power drill bit to make pilot holes for the screws you use in order to minimize splitting in wooden window frames and ease penetration of other types of window frames. After installation, clean the air conditioner filter regularly to optimize performance.

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