Sizing Your Air Conditioner

Your BTU requirement- This is probably the first and most important consideration. You want to get a unit with a capacity as closely matched to your needs as possible. A unit that is not powerful enough will run constantly and will never properly cool the room. A unit that is too powerful will "short cycle"- it will cycle on and off over and over again, only remaining on for short periods of time. Short cycling is bad for the compressor- it could substantially shorten the life of the air conditioner, and the air conditioner will not dehumidify appropriately- so while the air in your room might be a comfortable temperature, there could be an uncomfortable level of humidity. The ideally sized unit will run at its maximum capacity on the few hottest days of the year and run somewhat under capacity at other times.

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

Commercial applications (shops, offices, etc.)*: 400 sq. ft. per 12,000 Btuh

Computer rooms and telephone servers*: 250 sq. ft. per 12,000 Btuh

* This guide should be used as a rule of thumb and not subtituted for proper load calculation

* The content above excerpted from www.ehomeair.com