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Get the Most Out of Cooling

Determine the best unit size for your space

If you’re installing any kind of air conditioner, be sure to get the right size. A unit that’s too small won’t cut the heat, but an oversize system will waste energy. Match room size with cooling capacity, measured in British thermal units, or Btu (the quantity of heat required to raise the temperature of 1 pound of water by 1 degree at a specified temperature). Follow these steps to determine what size AC unit will maximize your cooling.

1. Calculate the square footage of the area to be cooled.

2. Determine the best approximate cooling capacity using the table below (capacity will differ depending on ceiling height).

550–700 square feet: 14,000 Btu
700–1,000 square feet: 18,000 Btu
1,000–1,200 square feet: 21,000 Btu
1,200–1,400 square feet: 23,000 Btu
1,400–1,500 square feet: 24,000 Btu
1,500–2,000 square feet: 30,000 Btu
2,000–2,500 square feet: 34,000 Btu

3. Adjust your calculations accordingly for these situations:

  • Reduce capacity by 10% for shaded rooms.
  • Increase capacity by 10% for sunny rooms.
  • If more than two people regularly occupy a room, add 600 Btu for each additional person.
  • If an AC unit is to be used in a kitchen, increase capacity by 4,000 Btu.