What Size Air Conditioner Do I Need

What size air conditioner do I need? When selecting an air conditioner for your home, remember that not all air conditioners are created equally. The best way to determine the size of air conditioner for your home is to conduct a load calculation. This calculation estimates heat gain and heat loss in your home and helps you select the proper air conditioner.

Consider This
When determining what size air conditioner will best cool your home, these factors need to be taken into account:

  • Climate
  • Direction home faces
  • Heat-producing appliances
  • Humidity levels
  • Insulation value in the home
  • Maximum number of square feet to be cooled and/or heated
  • Number of people living in the space
  • Number of windows

This Air Conditioner is Too Big
Purchasing an oversized air conditioner isn't a smart decision. A system that's too big will not remove enough moisture from the inside because the air cycle is too short. While the system does cool quickly, the air cycle does not run long enough to remove humidity from the inside of the home, and that leaves residents uncomfortable. The bottom line is that an oversized system consumes more energy.

This Air Conditioner is Too Small
Too small of air conditioner isn't a smart buy, either. The system won't cool sufficiently. Since the unit will always be trying to catch up cooling the house, the unit's energy costs will be high.

This Air Conditioner is Just Right
To find the proper size air conditioner, calculate the square footage of the area you need to cool. It's a simple calculation. Break the area into shapes to calculate square footage. For a square or rectangular room, multiply the length by the width. For a triangle section, multiply the length of the triangle by the width and divide by two.
Cooling ability is measured in British thermal units, or BTUs. Use this guide to determine BTU capacity.

  • 100 - 150 = 5,000 BTUs
  • 150 - 250 = 6,000 BTUs
  • 250 - 350 = 7,000 BTUs
  • 300 - 350 = 8,000 BTUs
  • 350 - 400 = 9,000 BTUs
  • 400 - 450 = 10,000 BTUs
  • 450 - 500 = 12,000 BTUs
  • 550 - 700 = 14,000 BTUs
  • 700 - 1,000 = 18,000 BTUs
  • 1,000 - 1,200 = 21,000 BTUs
  • 1,200 - 1,400 = 23,000 BTUs
  • 1,400 - 1,500 = 24,000 BTUs
  • 1,500 - 2,000 = 30,000 BTUs
  • 2,000 - 2,500 = 34,000 BTUs

Adjust For Accuracy
Once the square footage is calculated and you've determined the number of BTUs will most efficiently cool your home, you should make adjustments based on these factors:

  • Heavily shaded room reduces capacity by 10 percent
  • Very sunny room increases capacity by 10 percent
  • More than two people usually inhabit the area, add 600 BTUs for each additional person
  • Kitchen units should be boosted by 4,000 BTUs

While you can calculate the square footage on your own, a trained air conditioning professional may be the better choice to perform a load calculation on your home.

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