It's that time again, getting out the ladder and installing the in-window air conditioner. The accordion thingies that come with the unit are completely useless of course, unless you don't mind hot air, flies, mosquitoes, squirrels and anything else coming into the house through the gaps. Therefore, I have the problem of how to install the thing.

My normal method is the following:

  1. Hold the thing in by screwing it to a wood lintel that is closely fitted to the window, so it is solidly held in.

  2. Cut pieces of lexan or plexiglass to exactly fit the gaps on both sides.

  3. Climb up the side of the house on a ladder and install the lexan panels using duct tape. Make sure there are no gaps at all (very important).

  4. Cut insulation that fits the gaps. Go inside house and insert insulation pads on both sides.

  5. Cut more lexan to fit gaps in window on inside.

  6. Duct tape the inner panels to the window. Phew, finally done.

What a pain in the butt, and when October rolls around I have take the Jerry rig all apart again.

Anybody got an easier way of doing this?

  • Sounds like you have a good handle on things. I am from Alaska and am in favor of duct tape generally, but beware that it doesn't stick forever.
    – SDsolar
    May 21, 2017 at 4:53
  • Buy a unit that has a heater as well, and don't worry about October?
    – Matt Mills
    May 23, 2017 at 15:06
  • I think the solution is to just wait for the perfect answer here. By then it will be November and your problem is solved!
    – Hot Licks
    Nov 4, 2017 at 20:54
  • Does your air conditioner size change every year? Have any access to block styrofoam? Nov 4, 2017 at 22:17
  • How did you end up solving this? May 30, 2018 at 13:17

1 Answer 1


Take two pieces of 1/2" plywood, that have been cut to fit the width of the window and are 1-1/2"-2" taller than the A/C unit.

Cut out the outline of the A/C unit from the center of the plywood pcs. so that you've got a "collar" that can be slid down, like a yoke, or otherwise fit around the A/C unit.

Cut out "windows", in both pieces of plywood, on either side of the area where the A/C unit will be; maintaining at least 1" between the window jamb and the area the A/C unit will be and these "window" cutouts (so the plywood won't break). At this point, both pieces of plywood should be identical where the cutouts were made.

Cut two pieces of Lexan (or similar) that is 3/4"+ larger than the "window" cutouts in the plywood (another reason to leave a 1" space between areas cut-out). Glue (with something that isn't too permanent) into place and sandwich between the two pieces of plywood using carriage bolts to secure the plywood together. Or, glue, if you're confident all is lining up perfectly and will fit properly.

Using (black) foam pipe insulation, wrap the plywood edges and staple into place (staples on the side that will be outside...to prevent water from getting inside the tubing); including the edges that will abut the A/C unit. And give it a trial fitting around the A/C unit that is already in the window, to be sure the pipe insulation compresses enough for a proper fit. Shave the plywood where it's too tight a fit.

Note: a thin (half-width) strip of duct tape along the seam of the pipe insulation and plywood cutout will create a sort of "drip edge" or seal to divert rain water better than the staples alone.

Note: if the A/C unit tapers or has indentations at the bottom; such that the plywood would leave gaps if slide down like a yoke, first try cutting the shape of the A/C unit so it will slide into the plywood frame. If this won't work fitted pieces of insulation board (or piggy-backed pipe insulation), duct taped into position, will do (these will be what gets replaced each year).

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