Replacing a wall AC? will a window AC do?
July 4, 2012 10:43 AM   Subscribe

Do I really need a wall air conditioner? Can put a window one in the same place?

The ancient wall AC unit in our house has now gone full defunct. We've hesitated to replace it because of the expense, but now we've got some extra money and are thinking about replacing it.

I always thought that "wall" air conditioners were just window units installed in a wall, but now that I've started looking around online to price things out, I've discovered they are a whole different category.

What makes a wall AC different? Do I really need to replace the old wall unit with a new wall unit? Any chance I could just put a window unit in there? Because I'm noticing that the wall units I'm seeing are significantly more expensive than window units of similar strength. (And of course on top of the price of the unit, we'll have to add the cost of having someone install it.)

We live in a rowhouse with very limited windows, and I don't want to lose any to an AC unit, which is why I'm trying to stick with a new unit in the same place. Plus, there is a dedicated outlet for the AC currently. It's on the front wall of our first floor, and it cools the combined living/dining room area, so we need a sizable one, BTU-wise. The extra cost of a wall unit is no joke.

Can anyone provide any explanation/give any suggestions?
posted by leticia to Home & Garden (9 answers total) 2 users marked this as a favorite
Do you have a metal sleeve in the wall already? Also, how thick is the wall?
posted by unknowncommand at 10:50 AM on July 4, 2012

Your instincts are right: a hole in a wall is roughly equal to an open window. So, in that sense, you're good to go. You merely have to consider a few extra things, since it will be permanently installed: is the aperture significantly larger than the unit you're going to buy? If so, you'll need to build some kind of skirt around it (with some insulative batting for the winter months, maybe?). Either way, you'll need to caulk/seal the edges. And, since it's on the first floor, you'll want to find a good way to affix it so that nobody can kick it in and enter your home undesirably.
posted by thejoshu at 10:53 AM on July 4, 2012

I believe that the sleeve used by many wall units will obstruct airflow from the sides/top/bottom. A window unit may be taking air in from the sides and blowing it out the rear. If you block its ability to bring in air, it isn't going to be able to put the heat from the coil anywhere, and will probably burn itself out.

You can probably throw a small window unit into a wall sleeve, place a cutout around it, and not lose too much efficiency. As long as there's room for air to be drawn in and circulate, and by that I mean more than a teeny tiny gap, that may be doable. Your situation, however, sounds like you require the full amount of BTU's possible.

You may be able to find a window unit that is more compatible with this sort of thing than a typical unit. When we had a wall unit, I believe the unit came in both sleeve and window models, and they were very similar in design.
posted by jgreco at 10:54 AM on July 4, 2012

This guide was fairly helpful to me when I was considering this exact question over the last few weeks.

Basically, there are two kinds of wall unit, one that is more similar to a window unit except it's supported/bolted externally (sometimes called "slide-out" units), and one that fits into a sleeve (each brand has its own size of sleeve, though there is some leeway there). Sleeve units are vented in the rear, and the slide-out ones are vented on the sides, but towards the rear of the unit, so that the vents won't be blocked by the wall (they are usually for walls that are less than 8" thick). In contrast, window units are vented on the top and sides. They're also physically smaller.

Strictly speaking, if you put a window unit in the wall, it won't be vented correctly, and it can overheat and die, or have a shorter lifespan. Also, putting a new window unit in the wall voids its warranty, and it will be less efficient (i.e., more costly) because you'll have to fill more gaps between the smaller machine and the wall.

So it comes down to how risk averse/tolerant you are? Like the other commenters said, you could probably put a window unit in there, given sufficient space around the top/sides of the unit for ventilation, and the world won't end. However, if you own your place, I would recommend getting the correct unit, because it will likely last longer, and the warranty will be there, in case it's a dud. Prices on Amazon are better than everywhere else I looked (even neighborhood appliance stores, sadly), and if you sign up for a free month-long trial to Amazon Prime, you get free shipping (just remember to cancel!).

Another option is a portable unit. They are cheaper than through-the-wall units, and wouldn't obstruct your window as much as a window unit (though most have tubes that need to be vented through a window, it just doesn't take up the whole thing). I can't speak to their efficiency or durability though, because they don't work with my windows, so I didn't research them as much.
posted by unknowncommand at 11:34 AM on July 4, 2012 [1 favorite]

some window units can indeed be installed in a wall unit opening. if you find a nice window unit, find the install manual - Sears and Home Depot at least tend to link to them, or you can usually find them by googling the model number - and see if the unit allows for in-wall installation and all that. (I ended up reading a bunch of air conditioner installation manuals when I replaced my dead window unit last month and found that, at least for the kind I was looking at [230v 15A units, which aren't cheap either] they do seem to support this.)
posted by mrg at 11:40 AM on July 4, 2012

Also, if you're friendly with any of your rowhouse neighbors (or would like an opportunity to introduce yourself), you could knock on their doors and ask what they've tried.
posted by unknowncommand at 11:42 AM on July 4, 2012

Don't forget drainage. If you put a window unit in there it may not drain standing water correctly, which could damage your wall. Usually the sleeve is installed with a slight downward tilt toward the outside, but the build of your window unit will matter. (Personally I would get a wall unit.)
posted by zvs at 1:39 PM on July 4, 2012 [1 favorite]

It might be out of your price range, but have you considered a ductless heat pump for this application? Despite the name it also functions as an air conditioner and as a bonus during cold months can be used as a very efficient heater. Installation only requires a hole in the wall big enough to accommodate the coolant pipe between the internal and external unit so you can pretty much place them anywhere. One place I worked had one installed in the server room and it worked a treat for cooling, and was also a lot quieter than any wall/window AC unit I've ever come across. And despite the extra upfront costs, it may indeed pay for itself in the winter as a heat assist, lowering your heating bills.
posted by barc0001 at 1:50 PM on July 4, 2012

I've put standard A/C in a wall-hole before. Yes, the A/C might overheat. However, the price was so cheap, I'd have to go through a dozen before it'd be a bad choice vs. central air. I suppose I could have put them in the window, but there weren't any convenient windows in this case.

In my case, it was for the mother-in-law. Her unit had one GIANT A/C unit (plugged into 220 no less!) which I replaced with the largest A/C window A/C unit I could buy. That unit was actually a very nice fit and I doubt it will ever overheat.

For her bedroom, the hole was much smaller, although just as deep. We put in the cheapest unit we could buy and it's still working. I think it might overheat someday, but it was $88, so whatever. :^)

As for making it fit nicely, I just stuffed them in there, then filled all the gaps with foam. If you don't think you'll be removing it anytime soon, that expanding foam might be a good choice! I have the units pulled as far into the room as possible to ensure the cold air gets out of the vents and into the room right away.

The efficiency wasn't hurt much doing this, although I assumed it would be been terrible. They still blow plenty of cold air.

One last note: Put some wood or other material underneath so they are tipped back a little. Otherwise, during humid weather, the water will run forward, which, if the sleeve was poorly fitted, means water in your house instead of out of it. Or better, some units let you fit a drip hose to them
posted by shepd at 4:44 PM on July 4, 2012

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