How to jury-rig a window AC to work well with a window that's too small?

June 12, 2017 11:33 AM

I've discovered my new window is just a bit too narrow for my air conditioner. Please help me make an insulated tent (or something?) to keep hot air venting outward safely and (relatively) efficiently.

Literally > 1/8" wider and the window would be perfect! Argh.

Buying a new unit isn't in the budget, and altering the window isn't an option. So I'm left with putting the thing up on bricks right in front of the window and figuring out how to vent hot air outward and keep moisture from draining on to the floor. The latter seems pretty easy.

The pane opens vertically and goes a couple of feet higher than the top of the AC, so I want to create an insulated "tent" that would effectively keep the the heat-venting parts "outside." But:

a) I'm not sure what my best options for insulating materials are at a reasonable price
b) I want to be sure I'm not doing anything that's going to damage the unit, make it overheat, or turn it into an electrical or air quality hazard.

Like, how much clearance should the vents on the side have? Are there kinds of materials that probably shouldn't be close to them when it's going to be running for a few hours at a time? Are there insulated sheets or other flexible materials that are going to do the job or do I need to fashion some polystyrene monstrosity? Are there better adhesives than duct tape for creating the seals where the "tent" (or whatever) meets the window and window frame, or at seams in the insulation? Any other obvious concerns or hazards I'm not thinking of?

Thank you!

posted by poweredbybeard to Home & Garden (8 answers total)

One thing before you go this tent route: are there any fins or anything that could be unscrewed from the sides? Or any chance you could you put the unit on its side?

Also, is there any chance you could put the whole unit OUTSIDE the window and blow the cold air in? That seems marginally more possible than keeping the whole thing inside, although if there's any chance it could fall and hurt someone/itself, that's not an option, obviously.
posted by mskyle at 12:00 PM on June 12, 2017 [1 favorite]

Response by poster: I like your thinking with putting the whole thing outside! but I'm not on the ground floor and there's no safe place to put a ladder in front of my window to build a frame. And I don't trust myself to build a perfectly safe one anyway! As for putting it on its side, I doubt it'd drain properly if I did that...
posted by poweredbybeard at 12:09 PM on June 12, 2017

If you just need an eighth of an inch, you could remove trim from the bottom part of the window. Since you'd only be removing it from the part of the window the AC will be occupying, it won't make the sash loose or anything, and if you cut it out carefully you can always replace it later when you remove the unit.
posted by wierdo at 12:28 PM on June 12, 2017

It reminds me of things I've seen on boats, like this. Not exactly elegant. But you could use a roll of Reflectix and duct tape to make a non-permanent sleeve. I'm worried that any good solution would cost more than a new proper-fitting window unit. And hopefully you aren't too worried about burglars.

I assume you can't rotate it 90 degrees either...
posted by RobotVoodooPower at 12:35 PM on June 12, 2017 [1 favorite]

Yes, do keep the unit level. There is typically a drain pan on the inside side under the coil that catches water that condenses out of the air, and routes it to drip outside. Without that, water will be dripping on your floor if you're lucky, or onto electrical components inside the unit, if you're not.

Could you add a couple of pictures? Like wierdo pointed out, if you have a wooden frame, there may be a trim piece of the window you could just pry off, then replace later with a couple of finishing nails. Is it the main width of the unit that won't fit, or just the framing of the unit that holds it to the window frame?

If it's the main mass of the unit that's too wide, it'll be more difficult to remedy. The exterior portion of a window unit needs airflow over it to reject heat to, and gets very warm. If the whole unit is on the inside, you may have to resort to something like what RobotVoodooPower linked to, just in reverse. Plus, you'd want a fan on the outside side, to ensure air moves over the coil, or the interior portion won't cool effectively.
posted by BevosAngryGhost at 1:10 PM on June 12, 2017 [2 favorites]

You can't afford a new unit, but have you considered a trade? Perhaps you could post a craigslist or newspaper ad if you don't know anyone with a slightly smaller window unit who might be interested in an upgrade.
posted by MoTLD at 2:34 PM on June 12, 2017 [4 favorites]

Response by poster: The exterior portion of a window unit needs airflow over it to reject heat

I know they heat up, but I hadn't thought of the coil needing more active cooling... this is disappointing, but also helpful :)

It's actually part of the plastic window frame that's in the way: the part that keeps the upper, outer window pane in place and lets you open it downward if for some reason you wanted to do that. Not easily removed, and the landlord wouldn't appreciate me cutting it out.

I am curious what that boat thing is made of. Definitely the sort of setup I had in mind. And I guess if I'm already making my tent, it's not that much more effort to add a hole for a small fan to blow outward across the rear part too...
posted by poweredbybeard at 5:40 PM on June 12, 2017

Then would it fit in the upper part of the window if you open that instead?
posted by fings at 6:58 PM on June 12, 2017