In my bedroom I have a one hose portable AC unit, because my only bedroom window is a sliding window. Currently, I set up the window kit in the day and take it out before bed. The reason for this is because of the road noise at night from the street the window faces. Picture of window

To seal the window kit I am using foam pipe insulation around the edges, which works quite well. The main source of noise, however, is coming from the opening between the two sections of window in the middle. When the window is closed, the middle frame of the sliding section seals against the other frame, blocking out any noise. When the window is open, there is a gap created (approx 49 1/2" tall, 3/8" wide).

My first attempt at sealing the gap was to use half a section of foam pipe insulation jammed into the gap, which does block out some noise (and outside air) from getting in, but still not to a level where I can sleep comfortably with it installed in the window.

So, my question is what would be a good way to seal the gap?

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    – FreeMan
    Aug 19, 2020 at 12:22

2 Answers 2


I had this same problem and ended up using some foam piping I found in the window seal section at the home improvement store. The next best thing I could think of was cutting some foam to the exact fit of the window, compressing it before you open the window, then opening the window onto it, moving the foam into place as needed. If you use sound proofing foam, you might get a noticeable drop in noise. Other than that, I'd buy some good ear plugs.


If sight(decor/curb appeal) is not a requirement, maybe duck tape or newspaper (folded until it is the right thickness) and duck tape? Maybe even duck tape over your foam! Other options would be a rubber membrane like a door sweep. The challenge is in getting it to seal around the bottom and top of the window inside tracks. I am assuming this building is not owned by you? If you own the home, you could look into a through-the-wall kit for the portable A/C unit.

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