Sizing Window AC for room

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Jun 23, 2020
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The bedroom we want cooled w/ a window AC unit is 215 sq ft. That should be easily cooled by an 8000 BTU unit but it doesn't. We had an LG 8000 in a window that was the farthest away from the bed bc the powering on of the motor disturbed my sleep. But it didn't cool the room well. So then I got a different AC Midea ushaped and placed it flush w/ the bed. I have to start the unit in the mid afternoon to even get in to the low 70s at night. I've since read this Midea that just came out is getting poor reviews. So now I'm trying to figure out whether we need to go up to a 10000 until. I've read that if it's too large for the room it can end up getting swampy. We live in nnj where it's humid and days have been near 90 and nights are in the 70s. I like the room to be COLD. Like as near to 60 as possible.

Should I assume that the 1st AC was old and not efficient. (probably 5 years) and the new one is just lousy so I should stay w/ 8000 or should we move up to a 10,000BTU unit. I put dampers at the bottom of all doors to keep the cooler air from escaping. Thanks!
 

ryan_975

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An 8,000 BTU unit can remove 8,000BTU of heat per hour. So you need to know what your room’s heat load is. Is it in the sun? are there a bunch of windows? how well is it insulated? How many heat producing devices are running?

As an example, we have two rooms with window units, both 5200 BTUs. One room is on the East side of the house between the garage and another room. The other is one the southwest corner of the house. The southwest room had to keep the AC turned all the way down to keep it cool while the east room will freeze you out even turned just 1/2 way down.
 
Joined
Jun 23, 2020
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An 8,000 BTU unit can remove 8,000BTU of heat per hour. So you need to know what your room’s heat load is. Is it in the sun? are there a bunch of windows? how well is it insulated? How many heat producing devices are running?

As an example, we have two rooms with window units, both 5200 BTUs. One room is on the East side of the house between the garage and another room. The other is one the southwest corner of the house. The southwest room had to keep the AC turned all the way down to keep it cool while the east room will freeze you out even turned just 1/2 way down.
Well much of what you're asking is above my pay grade. I only need it for the night so sun shouldn't be an issue. The only reason I've been running it in the afternoon is bc it takes so long to cool down. Heat producing devices as in lights? A small bedside light. There are 3 windows. So given the answers to those any thoughts on whether to move to a 10000 unit? Thanks for answering.
 

travm

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Well much of what you're asking is above my pay grade. I only need it for the night so sun shouldn't be an issue. The only reason I've been running it in the afternoon is bc it takes so long to cool down. Heat producing devices as in lights? A small bedside light. There are 3 windows. So given the answers to those any thoughts on whether to move to a 10000 unit? Thanks for answering.
Get the biggest machine you can fit/afford.
Especially if the 8000btu you had before was insufficient. AFAIK AC technology hasn't advanced in the last 30 years, it's possible your unit was junk. I bought one once that didn't cool worth a damn, turned out the fan on the high pressure side was spinning the wrong way.

Having too much cooling capacity has never been complained about.
 

VanGoghComplex

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Your insulation (or lack thereof) is a big deal when you're trying to climate control a space. An 8000btu unit that isn't effective may become effective if you insulate properly. If you buy a monster AC to compensate for bad insulation you're going to waste money buying the unit and waste money paying for the electricity to run it.

Is it a rental space?
 

travm

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Your insulation (or lack thereof) is a big deal when you're trying to climate control a space. An 8000btu unit that isn't effective may become effective if you insulate properly. If you buy a monster AC to compensate for bad insulation you're going to waste money buying the unit and waste money paying for the electricity to run it.

Is it a rental space?
Buying a larger unit vs gutting your house / apartment, getting necessary permits, and re insulating your space is almost a no brainer. You will die before the electricity savings equal the cost of rebuilding your home.
 

VanGoghComplex

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Buying a larger unit vs gutting your house / apartment, getting necessary permits, and re insulating your space is almost a no brainer. You will die before the electricity savings equal the cost of rebuilding your home.
I'll assume you've never added insulation to anything. You don't need to gut, permit, or rebuild to add insulation to a single existing room. It's an inexpensive DIY project.

Obviously not everyone will be able to do it, but if you're able, it's a very easy thing to do.
 

zetachi

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Just replaced a 15K BTU unit that was probably 12 yo or more with a 12k Friedrich that i got through Greentoe. SO far its only been in about an hour but its quieter and so far providing the same level of cooling. We have an open 480 Sq/Ft living room in our apt with multiple windows and a few open rooms off it and its cooling the entire area. and its 90 here in NYC today.
 

travm

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I'll assume you've never added insulation to anything. You don't need to gut, permit, or rebuild to add insulation to a single existing room. It's an inexpensive DIY project.

Obviously not everyone will be able to do it, but if you're able, it's a very easy thing to do.
Depends on the locale.
I'm also absolutely speaking from experience.
In my area any time you add insulation, a building permit with inspections is required.
Have you ever removed a rooms worth of drywall?
Blowing a bit of insulation into the Attic is one thing, and still less than 1/4 of what would be required to make a difference.
Unless insulating means wrapping your interior walls with 3 layers of uline bubble wrap.
 

travm

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Really what you should do is have a proper mini split AC unit installed. More expensive for sure, but sometimes you should just suck it up and buy what you need.
 

VanGoghComplex

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Depends on the locale.
I'm also absolutely speaking from experience.
In my area any time you add insulation, a building permit with inspections is required.
Have you ever removed a rooms worth of drywall?
Blowing a bit of insulation into the Attic is one thing, and still less than 1/4 of what would be required to make a difference.
Unless insulating means wrapping your interior walls with 3 layers of uline bubble wrap.
If you have uninsulated exterior walls, you can blow insulation into the cavities through small holes that then just need to be patched. You don't need to tear off all the sheetrock.

I'm sorry you need a permit to add insulation. Talk about a nanny state...

I'll concede that it could be too much work to be worth it, but the situation you're talking about is worst-case. The last house I owned had insufficient insulation and it one a one-day project to fix it. Cut my electrical bill nearly in half and made my AC actually function.
 

travm

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If you have uninsulated exterior walls, you can blow insulation into the cavities through small holes that then just need to be patched. You don't need to tear off all the sheetrock.

I'm sorry you need a permit to add insulation. Talk about a nanny state...

I'll concede that it could be too much work to be worth it, but the situation you're talking about is worst-case. The last house I owned had insufficient insulation and it one a one-day project to fix it. Cut my electrical bill nearly in half and made my AC actually function.
Fair enough.
In Canada there are no "houses" with "no insulation". Just houses with bad insulation.
And every time you re-insulate, they (big bro) wants to make sure that it is properly sealed to prevent condensation from forming in the insulation and creating mould.

Its highly possible that the OP lives in the desert, and neither of these things apply.
 

freeagentt

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Here in Canada you need to apply for a building permit, but not to insulate your house or room. And if you do.. I've never seen it done before :D
 
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Thanks for all your replies. I'll reply here to most if that's OK.
i have no idea about the insulation. As I said we're in N NJ. It's a 50s split level. Yes we own the house. It seems to retain the heat in winter. How would you know how good the insulation was? There's probably not much down side to putting in insulation except making a mess of the walls bc we're not handy people here but I'll look into that. Of course that's not happens before I get another AC. Thanks for mentioning it. Our central air quit and we decided to tough it out bc of the expense and now no work bc of well you know. We're both performers so all gigs are canceled. We are considering mini splits. I guess we're against a wall so to speak in that we don't have many options. I'm going to get a larger unit and hope it'll do the job w/o a huge spike in the electric bill.

Thanks all for thinking this through and especially bringing up the issue of insulation. Stay cool!
 

Kardonxt

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8000 should be plenty for that size of a room. In my experience Windows ACs suck at quickly bringing down temps. If you want it to work right set the temp and leave it on 24/7.

I also like a cold room but any Window unit I have ever used only lets you set the temp down to ~ 65-68. If you need temps colder than that then the trick will be looking up the lowest temp setting each unit supports.
 

Format _C:

2[H]4U
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Jun 12, 2001
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The bedroom we want cooled w/ a window AC unit is 215 sq ft. That should be easily cooled by an 8000 BTU unit but it doesn't. We had an LG 8000 in a window that was the farthest away from the bed bc the powering on of the motor disturbed my sleep. But it didn't cool the room well. So then I got a different AC Midea ushaped and placed it flush w/ the bed. I have to start the unit in the mid afternoon to even get in to the low 70s at night. I've since read this Midea that just came out is getting poor reviews. So now I'm trying to figure out whether we need to go up to a 10000 until. I've read that if it's too large for the room it can end up getting swampy. We live in nnj where it's humid and days have been near 90 and nights are in the 70s. I like the room to be COLD. Like as near to 60 as possible.

Should I assume that the 1st AC was old and not efficient. (probably 5 years) and the new one is just lousy so I should stay w/ 8000 or should we move up to a 10,000BTU unit. I put dampers at the bottom of all doors to keep the cooler air from escaping. Thanks!
I would look for an old but working AC unit (back when things were made to last) I bet a big old 8000BTU would cool that room fine. The older the better. I would look for late 1960's until the mid 1990's as that is when the quality of units started to make a downward trend.

This might be part of the problem😁
I also like cold but not 60 even that is too cold for me. I keep that Mitsubishi unit set at 64 and it manages to keep the place around 65-67 depends on the outdoor temp and if I am cooking or even the sun hitting the window raises the room temp. The apartment complex I live in had Mini-Split units (Mitsubishi Electric) the unit cool the space quickly and they are very quiet, they are a great piece, when they work properly but don't count on them working properly for long, and when they do fail that is an expensive repair cost. Luckily when the unit in the apartment I live in failed the management had to pay that bill it was around $600 for the part (control board) and $350 for the labor to install it as the whole indoor unit has to be taken apart before you can even see the board.

8000 should be plenty for that size of a room. In my experience Windows ACs suck at quickly bringing down temps. If you want it to work right set the temp and leave it on 24/7.

I also like a cold room but any Window unit I have ever used only lets you set the temp down to ~ 65-68. If you need temps colder than that then the trick will be looking up the lowest temp setting each unit supports.
I had once had a Kenmore 253.79085 8000 BTU unit actually made by Frigidaire Electrolux for Sears/Kenmore.
That unit really sucked but the thermostat did go down to 60.

I mis those old units. I remember when I was a kid there was a big old AC in the dining room area of the house I used to live in, I don't remember the brand or BTU rating (but it was a really huge unit) the one thing that I can remember about it even today (this was probably 30 something years ago) it had a setting on one of those knobs that said "Run Constantly" which ran both the fan and the compressor constantly (you had to manually turn it off if you got too cold) just as the name imply s the house could get to 50 and that big old thing would not care.
 
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Joined
Jun 23, 2020
Messages
6
8000 should be plenty for that size of a room. In my experience Windows ACs suck at quickly bringing down temps. If you want it to work right set the temp and leave it on 24/7.

I also like a cold room but any Window unit I have ever used only lets you set the temp down to ~ 65-68. If you need temps colder than that then the trick will be looking up the lowest temp setting each unit supports.
Really? The ones I've had went down to 60 degrees so I just assumed that was true of them all. i ordered one so I've got to make sure it goes that low. Thanks for the heads up.
 
Joined
Jun 23, 2020
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8000 should be plenty for that size of a room. In my experience Windows ACs suck at quickly bringing down temps. If you want it to work right set the temp and leave it on 24/7.

I also like a cold room but any Window unit I have ever used only lets you set the temp down to ~ 65-68. If you need temps colder than that then the trick will be looking up the lowest temp setting each unit supports.
I just looked and the one I ordered does go down to 60.
 

travm

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Feb 26, 2016
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522
Here in Canada you need to apply for a building permit, but not to insulate your house or room. And if you do.. I've never seen it done before :D
It varies between municipalities, but every one I've lived in (2) required it for any time you added insulation. Doesnt mean everyone always took a permit, but you were supposed to.
 

drutman

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Jan 4, 2016
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Down here in Texas we have high humidity and air temps, heat index is around 110 degress F with RH of 80%. I would buy a unit with 240 V power not 110 V more efficient.
At best a system will provide a Delta T of 25, so the thermostat going to 50 or 60 is BS. If it is 100 outside at best 75 inside. We have a 8K central air unit that will not pull below 75 in the summer too much load to remove even with insulation. At night outside air is still 85 F.
 

freeagentt

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Dec 5, 2018
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117
When its +30-40c out our AC can only maintain 74 inside, 75 if you don't want it to run constantly. When its -40c outside we try to keep it at 71 :D

My computer loves the winter, best overclocking happens I crack a window lol.
 
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