I have a large sliding window that is 53 inches top to bottom and I want to install a portable air conditioning unit. The kind that don't sit in the windows but vent to the window. The window exhausting expander thing that come with these units seem to never be large enough.

Can I just use some plexi-glass or something to extend the extender or is there a better way?

Update: I found one large sliding window vent kit, but I think its just for edgestar ac units and I'd rather not have to buy such a kit if I can get a good seal some other way.

enter image description here

  • 1
    there's always duct tape :-)
    – BMitch
    Commented May 18, 2011 at 19:53

2 Answers 2


You could build a wood frame that fits in the window with an interior hole large enough to accommodate the AC unit. This also has the advantage that you won't have to hold the window open, while juggling the unit into place. You can install the light weight frame, then slide the unit into place.

I built one when I lived on the second floor of an apartment building, because I was always afraid I would drop the unit out the window while installing it. I used foam tape around the exterior and interior of the frame, to make sure I got a good seal around the window and AC unit.enter image description here

For a unit that only vents through the window (not sits in it), you could build a smaller frame with a port to allow the vent to pass through. Filling the interior of the frame with Lexan will reduce the amount of wasted window space.enter image description here

(You could always use smaller lumber for your frame, if you want it to have a lower profile. The frame size in the image is just an example, to illustrate the idea).

  • By Portable AC unit, I mean the kind that don't sit in the window, but vent to the window. consumersearch.com/portable-air-conditioners Commented May 19, 2011 at 12:01
  • Nice pictures, my windows slides sideways, but the same concept should apply, I will just put the vent opening all the way on one side. Commented May 20, 2011 at 17:23

The simplest and most cost effective solution will be to simply use a piece of thin wood like particle board or plywood to fill the remaining space that isn't sealed by the window kit that came with your unit. this probably wont give you a great seal though.

A better option might be to just use a long piece of wood and cut a hole similar to the one in your original window kit slider and attache the vent hose to that. This will be most easily done with a router or Dremel tool.

That's just my two cents based on what I've seen in the past. I'd be curious to know how you ended up solving the problem (if you have). I've seen some really creative solutions before and everyone seems to go about it differently.

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