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How to Install an Air Conditioner

When installing a window air conditioner, following the instructions that came with the unit is important, because different units have different requirements.

When you're choosing an air conditioner, it's important to size it correctly and locate a suitable window for it.  Most air conditioners fit well in double-hung windows, but not all will fit in other types, such as horizontal sliders.

Moreover, if you install you air conditioner in a window that gets full sun, the machine's performance will suffer and you'll end up paying more to run it.  An essential part of the installation process is **sealing the area around the air conditioner** to prevent air flow.


Choosing the Right Air Conditioner

When it comes to air conditioners, "[size](http://wwwpopularmechanicscom/home/how-to/a6030/how-to-install-a-window-air-conditioner/)" refers to physical dimensions as well as cooling power.  Both are crucial -- your air conditioner has to fit in the available space and it must be powerful enough to cool the room.

  1. Choose a window that's close enough to a power outlet to plug in the air conditioner, and is preferably **in the shade**.
  2. Open the window as far as it will go and measure the dimensions of the opening, using a tape measure.
  3. Determine the area of the room in which the window is located by measuring the room length and width in feet, and multiplying these numbers together. If the room opens into another, and there's no door, include the area of that room too.
  4. Use the total area to calculate the number of BTUs of cooling capacity you need. **Add** 10 percent if the window is in the sun, 4,000 BTUs if the room you're cooling is a kitchen and 600 BTUs for every person except yourself who shares the room.
  5. Consult your dealer or a manufacturer's website to find a unit that has a sufficient cooling capacity and will fit in your window.

Installation Procedure

  • You can drop some window air conditioner units into your window and secure them to the window frame, but some are too heavy for that and require a support bracket. The bracket typically comes with the unit. Consult the instructions for the proper way to install it.
  • Tip

    Be sure to note whether the unit should be installed with a slight tilt to the outside or level.

    Things You Will Need

    • Epoxy wood filler
    • Window cleaning supplies
    • Screwdriver
    • Ladder
    1. Make any needed repairs to the window frame, including filling rotted wood and securing loose trim. Clean the windows -- they will remain open, and if they are dirty, you won't be able to do anything about it until you remove the air conditioner.
    2. Secure the support bracket -- if there is one -- to the window frame, using wood screws to secure it to wood or vinyl framing, or sheet metal screws to hold it to metal. The brackets may have braces that must be secured to the exterior siding, so be sure you have a ladder tall enough to allow you to do this.
    3. Lift the air conditioner out the box with the help of a coworker and set it inside the window. Be careful when doing this -- air conditioners often have **sharp corners** that can catch on your clothing.
    4. Secure the unit using the method described in the package instructions. If the unit has a bracket, the air conditioner should fit securely inside the bracket and be secured with the screws that are provided.
    5. If the unit doesn't have a bracket, close the window and secure the air conditioner to the window frame by driving screws through the holes provided in the flange that extends around the center of the unit. Some units are provided with [L-brackets](http://www.homedepot.com/c/how_to_install_window_air_conditioner_HT_PG_AP) for this purpose.

    Sealing the Window

  • The accordion panels that come with most air conditioners provide a poor seal that allows hot air to enter. This makes the air conditioner work harder and costs you money. Replacing these with **foil-coated foam panels** is one of the recommendations the [U.S. Department of Energy](http://www.nrel.gov/docs/fy13osti/58187.pdf) makes for sealing the window and keeping the room cooler when the air conditioner is running and warmer when it isn't.
  • Things You Will Need

    • Screws
    • Foil-backed foam insulation
    • Weatherproof tape
    • Closed-cell foam backer rods
    1. Extend the retractable panels on either side of the air conditioner and secure the edges to the window frame with screws. Pull out the vinyl accordion material and fill the gap with rigid foam insulation. The panels must be **foil coated** to provide protection from rain and snow. Tape the panels in place from inside and outside, using weather-resistant PVC tape.
    2. Purchase closed-cell cylindrical **foam backer rods** to install between the window and the top of the air conditioner in lieu of the foam strips that came with the unit. Stuff these backer rods between the air conditioner and window and in any other visible gaps.
    3. Create a **barrier** to fill in any window space that remains open after the air conditioner is installed, using plywood and foam insulation. You'll probably need such a barrier if you install the air conditioner in a window that slides horizontally. Secure it in place with weatherproof tape.

    Things You Will Need

    • Caulking gun and waterproof caulk
    • Measuring tape and pencil
    • Air conditioner, mounting hardware, foam insulation (usually provided by manufacturer)
    • Screwdriver and screws

    About the Author

    Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since 1975. As a landscape builder, he helped establish two gardening companies.