What size window A/C unit would be most efficient for a 280 sq ft room?

Question

What is the formula for Btu vs room size?
I don't want this to be oversized either as I don't have a lot of power options & I'm trying to squeeze everything I can from (1) 15Amp circuit.This room will also have (2) c. fans, a mini-frig, (2) small flat screen tvs, a stereo & some lights.
Because of all this & my reluctance to put in another circuit, it needs to be (as close to) exactly the right size unit as possible so it'll work, but not pull too much amperage.

Answer 1

Assuming you don't really want to see the engineering formula for calculating BTU vs room size, rate of cooling, total temperature drop, etc, see this table http://www.lowes.com/lowes/lkn?action=howTo&p=BuyGuide/AirConditioner.html which includes a chart halfway through the article that suggests your room would best be suited with a 7000 BTU A/C. These typically run at about 850 watts. Assuming you are on a 15A circuit, this leaves you with about 500 watts to spread over your other fans/frig/TV, etc. If you have a big stereo, you may need to change your music choice from "hot hiphop" to "cool rock" to avoid blowing your circuit breaker. LOL.

If you add up your power consumption and find an AC makes you give up too many of your toys, consider using a smaller AC or an evaporative cooler like this http://www.amazon.com/Sunpentown-Portable-Evaporative-Cooler-purifier/dp/B0007W03IK/ref=pd_bbs_9/102-2621557-3174512?ie=UTF8&s=home-garden&qid=1189064097&sr=8-9 . This evaporative cooler is only 60 watts, leaving plenty of power for your other devices. Another advantage is that it is a lot CHEAPER to run than an A/C because there is no compressor (in this comparison, it is about 8x cheaper). Main disadvantages are that it will not cool the room as cold as an AC, you need to periodically fill the cooler with water (after several days), and it does not work well in a high humidity environment.

Answer 2

Some fact and figures by Fedders Air Conditioners I think 5000 btu's is a little on the light side. I would run a seperate circuit regardless, as you see they recommend 7000 btu's.

240 sq. ft. 7,000 Btu. X Chassis models– fits between 19" to 36" width by 12 3/4" minimum height window opening 125 volts 15 amps
From another source sizing requirements:
FOOTAGE BTU'S REQUIRED

250-300 7,000

300-350 8,000

350-450 10,000

450-650 12,000

650-850 13,000

850-1,100 18,000

1,100-1,400 24,000

1,400-1,800 25,000

1,800-2,500 29,000



Please note-
- Add BTU by 10% for sunny areas
- Add BTU by 10% for second story (or higher) rooms
- Add 4,000 BTU if area to be cooled is in the kitchen
- Add 600 BTU for each additional person (using room) over 2 persons

Answer 3

I agree to a degree with answer one. a room that size IE: 20 x 14 can be made comfortable with a 5000 BTU window unit, and they are less than $100, and if it's a dedicated breaker at 110 you'll have no problem.

The issue is a bit larger however, in that the room you wish to cool should likely be closed off for maximum effect. Obviously if there are doors open, or an open passage way/arch, to another room; you'll not only overwork the unit, but the power drain will be more.

Without knowing at all the current electrical setup regarding what receptacles are on what breakers, it's a bit nebulous to say.

Most obvious initially is for you to know what appliances/etc. are on what breaker/ breakers. I suspect for the AC; you need another. Your drain/load is probably close to max now, if you happened to have everything you mention, functioning on one circuit.

Steven Wolf

Answer 4

Considering your 15 amp power circuit, I would use the smallest size. 4000 or 5000 btu will cool 280 sq ft no problem. Smaller ones are also quieter.

Answer 5

The general rule of thumb is 600 square feet per ton of cooling. I would suggest a 1.5 ton unit. You also need to check the opening size to be sure whatever you buy will fit.