I'm living in an apartment where my bedroom has no windows opening to the outside of the building, only one window which opens into the living space.

As such, the room is tough to ventilate and gets noticeably warmer than the rest of the apartment.

I've bought a portable air conditioning unit (10,000BTU, standard 6" diameter exhaust hose) and extension hose, and I want to vent the exhaust air out the window into the living space. I realise this isn't ideal but it's much easier to ventilate the living space.

I need to seal the window to stop the hot exhaust air coming straight back in, and the cold air escaping out the open window. The problem is, due to the style of the window, regular sealing kits for air conditioners won't fit.

Here's the window:

enter image description here


I've been looking at dust covers for doors but they're all too large. Has anyone got any ideas how I might seal the window while still allowing a relatively airtight gap for the exhaust hose to be put through?

  • What "living space" are you planning on venting this hot air into? Is it another part of your apartment or is it the common, shared hallway to the other apartment doors? If it's part of your apartment, you're going to make the rest of the place hotter which will make it harder to cool the bedroom. If it's a common hallway, you'll make your neighbors mad.
    – FreeMan
    Commented Apr 25, 2022 at 17:13

3 Answers 3


Ignore the window. Seal a flat sheet of something to the window frame on the room side, with a 6" hole in it for your duct.

Something - Plexiglass or other clear plastic sheet if you want the light and are trying to do a "nice job." Cardboard and duct tape if not. Or something else, it really doesn't matter what, functionally.


A sheet of plywood. Most better lumber yards will sell you a cut piece to your specified dimensions that will sit inside the notch on the inside. You can then cut the openings exactly as you need for your "in" and "out" pipes. Tape that down with quality TV production quality gaffer tape so it removes without leaving residue.

I need to seal the window to stop the hot exhaust air coming straight back in, and the cold air escaping out the open window.

You can't avoid that, since you bought a 1-hose portable unit.


You know the air that goes out the hose? Where does that come from? It comes from the dry cool air that is inside the room - air you just paid to air condition. And then, that draws a negative pressure on the room, which means it is sucking in hot wet air from outside, through every leak in your house.

  • The incoming outside air is hot, and needs to be re-conditioned.
  • The incoming outside air is humid! To condense 1 pound (1 pint) of water, 970 BTUs of air conditioning must be wasted, last time I did the math I found this was using most of the A/C unit's capacity.
  • Since it's sucking in humid air, it fills the condensation tray much faster so the unit stops much more often.
  • It is sucking in allergens and pollution too.
  • If you are drawing air from the rest of the house or building, you are making that space hotter and wetter. That will cause condensation later, and mold.

But there's a simple solution for this: send it back and get a 2-hose unit. Plenty of room on the sheet of plywood for a second hose port. Now, it is getting its "process air" from outside and putting it back outside. The cool dry air in the room stays in the room and does not need to be dehumidified over and over. And your condensate tray gets emptied a lot less often.

  • 1
    At least in the US, I have found 1/4" or 3/8" thick HDPE plastic (cutting board material) to work well for these sorts of situations. It can be cut easily like wood, but does not rot or absorb water.
    – Armand
    Commented Apr 25, 2022 at 19:13

Based on other answers here, I managed to find a company manufacturing the required covers:


"quentin_bc" is the seller name on eBay if the listing goes dead in future.

Hopefully this is helpful to anyone else who comes across this post in future.

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