Sorry about posting my question in the answer column. I'm new here. Anyway, maybe somebody who knows a thing or two about A/C units can help me. I NOW know you shouldn't put a window a/c unit in through the wall because of the vents. I'm really glad some of you pointed that out as I read the answers.However, I already installed a window unit through the wall- studded it, insulated it, caulked everything necessary. After reading that this is a no no, I checked mine and I have about 3 inches of vent inside and about 4 inches outside. I don't want to yank this thing out and was hoping someone could suggest something. Can I buy something from a good hardware store to remedy this? Could I just cover up the inside 3 inches on both sides? Appreciate your help.

  • You can add photos from inside and outside by clicking "Edit" above and copy/pasting the photos in or using the editor tools. It will be easier to answer if we can see it.
    – jay613
    Jun 15, 2023 at 23:50
  • Do you mean that the side walls of the A/C have vents, and some of that venting is inside the wall? If that is what you mean, you need to remove it. There is a clear open path through those vents between the outside and the wall void. Water, and anything small enough to fit through the vents, can get into your walls. And if the condenstate is dripping into your walls instead of to the outside you won't know until the damage is substantial.
    – jay613
    Jun 15, 2023 at 23:52

1 Answer 1


Well, that's a disaster that won't wait too long to happen.

If you have a window unit, you'll have to give it something that looks a lot like a window, though it does not need to be a window. But it needs to be a larger hole than the unit, with only a thin section near the inside the size of the unit, that's equivalent to the window jamb that the unit would normally see - so perhaps 1.5-2 inches thick at most.

The rest of the hole through the wall would need to be framed out, finished/trimmed and flashed like a window frame, so that it's weathertight and sheds water, and should have 3-4 inches of clearance on each side and probably 6 or more inches from the top of the unit for ventilation space, all the way up to that thin interior part.

This was, of course, madness. Self-installable mini-split units exist. But I assume you'll be doubling down on using a window unit in a hole in the wall rather than fixing the hole in the wall and installing a mini-split that only requires a small hole for the lineset. So the majority of the hole needs to be larger for proper ventilation if you are using a window unit in a hole in the wall.

Without proper ventilation, the heat pump (cooling only version, that we call an air conditioner) can't move enough air through its "hot" coil where it rejects the heat from inside your house that it gathers from its "cold" coil inside the house. So it will overheat, run inefficiently, and quite probably fail soon.

  • Through the wall units exist too. You install the sleeve in the wall, then slide the unit in. They often aren't even that expensive, though more than a cheap window unit.
    – KMJ
    Jun 16, 2023 at 3:54
  • There are units available that were designed to work in a window and/or a wall.
    – Gil
    Jun 16, 2023 at 5:06
  • Wow, sounds very complicated. Just for the record, The window unit is through the wall with the outside end in a screen house, and open to air but not any water. I definitely am not going to yank this unit, so I will have to come up with something. The side vents are bringing air into the unit while the back blows air out. I think I'm going to take the front part of the unit out to check how much of the side exhaust actually is inside the sides of the wall. If any air is coming from the outside into the walls it, can I just cover it with some fire free insulation and aluminum?
    – Larry K
    Jun 17, 2023 at 18:42
  • Yes, I think that I shall do that. That, I will do. Thanks
    – Larry K
    Jun 19, 2023 at 0:27

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