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I just moved into a new apartment and they have a 25"x 15" pre-built wall sleeve for a wall AC unit. Not knowing the difference, I purchased the extravagantly less expensive window AC unit that has exhausts on the side and on the back. Realizing this, I figured that (with some internet searching) the unit may heat up because it isn't exhausting properly. If I have 1" on each side of the AC in the wall sleeve, is it good enough for exhaustive purposes?

Also, what would you do for affordable cooling on a first floor apartment with a 750 ft^2, 2 BR, apartment?

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A window mounted unit might be good for a small room, but not sufficient for a larger apartment living space. –  Matt Jul 23 '13 at 2:46
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3 Answers

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Window AC Clearances

You should check the manual that came with the AC, it might tell you minimum clearances. My window AC unit only says:

Side louvers and the rear of the air conditioner must have clear air space to allow enough airflow through the condenser, for heat removal.

I would say that 1" does not meet that requirement, particularly if the sides of the sleeve extend out past the end of the AC.

Sizing the AC

You didn't directly ask about the difference between the window units and the thru-wall models, but I agree with @Vitality that the price jump probably has a lot to do with the size of the unit. If you're trying to cool 750 ft^2 you're going to want to get a bigger unit than the $99 budget models they sell at Walmart. According to this Energy Star chart, you'll need a unit with around 18,000 BTUs/hr of cooling. If you get a unit that's too small it will just run and run but not cool or dehumidify the apartment, wasting you money. Plus it will probably burn out the compressor faster since it's not getting a break.

How To Cool An Apartment

Besides the AC, here are things that can help you keep the apartment cool:

  • Get curtains and close them during the day, especially if you're not home. Preferably blackout curtains. Lots of heat enters the house as solar radiation and you can prevent it if you keep the light out. If you're on a budget, Home Depot et al sell blackout roller blinds that are pretty reasonable.

  • Switch your light bulbs to LEDs (or CFL, if your budget requires... but spring for the LEDs if you can, they're better and will save you money). A 100 watt incandescent light bulb puts out almost 350 BTUs/hr in heat. If you have a bunch of those on, that's going to really going to add up.

  • If the temperature is cool at night, fans in the window can help exhaust hot air and bring in cool air from outside. I'm not a big fan of fans just circulating air inside, like ceiling fans and tower fans, since they don't actually cool the air. But some people like to feel the breeze. Definitely shut those fans off when you leave otherwise you're just wasting electricity and heating up the room.

  • Use the stovetop exhaust fan when you're cooking. It will remove the hot, humid air. Same thing for exhaust vents in the bathroom during/after a shower.

  • Basically anything else that reduces your electrical usage will also reduce heat in the apartment. E.g. I like to put my rice cooker on the porch even if I'm not eating outside.

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These are all great ideas. We do currently close our windows and draw our blinds (non black out currently), when we leave for work and it does help. I am inclined to believe that the "recommended" amount of BTUs is somewhat of an up-sell on lowe's, energystar's websites. I feel as though a 10K to 12K would work for my situation. What do you think about that? –  Scott James Walter Jul 23 '13 at 13:17
    
I too would be skeptical of a Lowes marketing poster, but EnergyStar is a government program designed to reduce energy consumption, so I don't know what their incentive would be to upsell you an AC. I personally would not undersize an AC by that much, although of course I don't know the details of your situation (heat, sun exposure, temperature preference, budget). Keep in mind that if you're cooling an entire apartment, energy star actually recommends 22k BTUs/hr (+4k for the kitchen). The cost of the AC is small compared to the cost of the electricity it uses. –  Henry Jackson Jul 23 '13 at 13:47
    
Thank you for the information! –  Scott James Walter Jul 23 '13 at 14:28
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I'd say that if the wall is projecting in front of any more than 1 inch width of the side exhausts, you do not have enough clearance for proper operation.

You could actually mount your window A/C in a window is about the only affordable option. Honestly, unless you have lots of windows or A/C is not that important, you are going to need to spring for a proper wall unit.

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I might be wrong but every single window AC i have ever seen has fins on the back and that's where the heat is exhausted. Moreover, I suspect there's really no difference between the wall and window mount acs. The wall ones might be pricier because they are usually more powerful as they are intended to cool bigger space. But inside those units are identical.

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The main condensor fins are usually on the back but most window units have additional vents on the sides and top... maybe air intake? But I agree, the size of the unit is probably the biggest predictor of cost. –  Henry Jackson Jul 23 '13 at 1:11
    
Yeah, I believe that the fins are for intake to take air off of the massive heatsink fins. Similar to a heatsink for a PC, I presume? –  Scott James Walter Jul 23 '13 at 13:15
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