How to install a window air conditioner

Installing a window air conditioner somewhere in your home can change your life dramatically in hot climates. If you have no central A/C or the one you have just isn’t strong enough, then you have good reason to get some extra cooling power. These appliances work well in rooms or sections of your house that tend to heat up, as they can isolate an area and make it livable again.




But how do you complete a window air conditioner installation easily? Many people’s feel they are heavy and need professional mounting, otherwise they’ll tip right out the window. And what about blocking spaces within the window that the unit doesn’t cover? These and other questions require real answers. Below you’ll find such answers to help your installation not just go smoothly, but give you the confidence to do it yourself.

Things to consider before installation

Before you get started and even before you make your purchase, it’s a good idea to cover the basics of adding a window A/C unit.

  1. Measure the size you need
    calculate how many air conditioning BTUs required for your space
    – get the size of your window to ensure the unit will fit (measure to fit full casing of unit, they are usually fully assembled when installed)
  2. Consider electrical needs of A/C
    – install your window air conditioner near an outlet or have one put in (most require a 220V outlet)
    – check your breaker box and see how many amps the circuit you plan to use can handle (breakers should list amp capacities)
    – do not use an extension cord  as can heat up and lead to underpowered AC unit (compressor draws a lot of power)
  3. Check the window
    – it goes without saying that you’ll need a double-hung window to install a room air conditioner like this
    – choose a window most central to your room
    – choose a window that is in a shaded spot if possible (this helps performance significantly)
    – make any repairs to the window first, such as repairing any rot on sills/trim or siding
  4. Mounting considerations
    – newer are lighter and don’t need a bracket like older ones that required it
    – as a general rule, outside bracing needs to be used on units with casing that extends more than 12″ beyond outside sill (adjust angle with leveling screw if available)

5 Steps for a window air conditioner installation

Now the fun begins. In most cases you should have a good instruction manual with your unit. But some brands don’t actually provide good instructions and/or you may be re-installing a used window A/C, and are going about this blindly. Follow these steps to properly install your window A/C:

  1. Install mounting bracket if needed
    – do this for older, heavy units you may be relocating
    – use screws to secure to windowsill on top and siding on bottom (bracket should have pre-drilled holes for self-tapping screws)
    – if you don’t have screws provided, use sheetmetal screws on a metal frames or wood screws on wood and vinyl frames
    – use a level to ensure unit is level from left to right, and slightly pitched toward outside to allow condensate to drain or kick out
  2. Place in window
    – move accordion panels out of the way and open window more than necessary for ample room, then close to help hold in place as you position unit in final place
    – if older unit has casing, slide casing into window opening and screw to sill and sash first if possible
    – casing and/or unit should be placed tilting slightly down to the outside as mentioned above
    – always lift unit from base or bottom pan, never pull or lift from plastic pieces
    – be careful not to damage fins or electrical wiring while handling
  3. Position accordion panels
    – pull side panels tightly against unit and frame (your window air conditioner installation is almost done!)
    – if using mounting frame, secure unit to it (if necessary, drill pilot holes first before driving down final screws)
  4. Screw in angle brackets
    – use brackets on upper sash to keep window in place (unit can push up against window forcing it up)
    – your install kit should come with these angled “L” brackets, but they are easy to find at hardware store
  5. Fill open gaps around A/C unit
    – use foam weather stripping on large gap on top of upper sash (it’s now open, so there may be gap)
    – check around accordion sides (expandable curtain/panels) and use weather stripping (foam rubber tape) to make things airtight
Installing a room air conditioner on the wall?
Sometimes you just don’t have the right kind of opening for a proper window air conditioner installation. The alternative is a bit more work, but it has some advantages when it comes to placement. You should pick a central spot for the room as well as use an eastern or northern wall of the house if you can to avoid directly sunlight on the A/C. Here are some tips and steps to follow when mounting your A/C on the wall:
  • mark an outline on outside wall first and start cutting your opening there
  • cut 1/4″ beyond your mark to allow ample spacing (you can fill excess space later with caulk)
  • use a straightedge (straight wood tacked to outside of house and follow with skill saw as you cut)
  • cut through siding and sheathing (stop when you hit studs)
  • from inside, cut through drywall or plaster/slats and then actual framing members (2×4 studs)
  • install a header (top) and sill (bottom) and jambs on side to support unit (you’re essentially creating a hole as you would a window)

When your opening is complete, you can follow the steps above for installing a window air conditioner in a double-hung window (you just won’t have a window sash).

The basic steps above should help guide you to a successful window air conditioner installation. If you have extreme winters and want to remove your A/C for the cold season, you’ll already be a pro come summertime when you need to get it up and running again. If you plan to leave it in the window year-round, you can buy a cover for the cold months to help keep your A/C clean and have it last longer.

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