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Thread: what BTU size in this case

  1. #1
    DIY Senior Member DIY's Avatar
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    Default what BTU size in this case

    Total sq. ftg. in this 2 bedroom apt. is 585 (L x W) of unit. From the 12' x 15' living room area you can see the open kitchen and in the kitchen is a zig zag shaped 2 x 4 partion wall then a bathroom on the other side of that partion wall. Those 3 rooms seem to be the easiest for a single window a/c unit that would be located in the front of the living room facing all of those 3 rooms to cool fairly easily and pretty quickly. However, the 2 bedrooms are located where the cooled air will not be so easy to get to them not to mention the walls around those rooms and the only air access would be via the bedroom doors. The living room and the 2 bedrooms each have a ceiling fan and they move air big time. Could one big a/c unit cool everthing if installed in living room? I have read sizing BTU's to sq. ftg. charts they seem pretty accurate as all i have read are the same,but there are also considerations some suggest while figuring a/c size like:

    *add 4,000 btu's if there is a kitchen to the initial applicable size.
    * another says add 4,000 btu's to every room attached to the kitchen.
    *another says add 1,500 btu's for every window that gets considerable sunlight.
    * and some charts have even said it Is possible to cool multiple rooms with one a/c located carefully and taking into account all needed to be cooled....Of course no details on that!....(laughing slightly)

    Many thanks to all !

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    The only way to accurately figure this is to know the location of the house, orientation, insulation levels, windows, sizing and orientation, and the size. You've only provided a very small amount of the info if you want to size the thing accruately. Ballpark sizing charts are often oversized, and the worst thing is an oversized a/c unit. Ideally, it runs constantly and just maintains the desired temp. This dehumidifies the air and there is little swing in temp. Obviously, no year has all days the same, so you size for the worst average (or a little less), and live with it being a slight bit warmer on that hottest day of the century.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Plumber jimbo's Avatar
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    The "add" figures you are quoting refer to CENTRAL air conditioning. The biggest problem using a single wall/window unit is that no matter how big the BTU, you don't get good circulation of the cooled air into the other rooms. In theory, 10 to 12 K btu will certainly cool 575 sqft, but you won't feel very cool in the kitchen or bedroom.

  4. #4
    DIY Senior Member DIY's Avatar
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    Hi Jimbo and thanks for the reply. The charts and the "add" figures came directly from several window unit a/c brochures,how to size them with this chart and considerations to figure in etc.
    Here is the chart the 3 or 4 I looked at had:

    Sq.Ft. Cooling Area BTU'S
    150 10'X15' 5,000
    250 10'X25' 6,500
    350 14'X25' 8,000
    500 20'X25' 10,000
    640 20'X32' 12,000
    900 25'X36' 15,100
    1,170 30'X39' 18,000
    1,672 38'X44' 25,000

  5. #5
    Plumber jimbo's Avatar
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    I will reiterate that all the BTU in the world don't help when the air doesn't circulate. Of course, you have to put in the A/C, and it is what it is. What you can expect is icy cold directly in front of the unit, and much warmer in the outer rooms.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    You are trying to "blow" air into a room, but there has to be some way for air to get out of the room so the cool air can get in. It is unlikely that the unit's blower would create the air movement needed to get it into those rooms, so unless you added local fans, not ceiling fans, to move the air from the big area into the side rooms, they will remain warm, regardless of how cool the main area is.

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