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What size air conditioner do I need for my home?

If you’re in the market for a new air conditioner, make sure you purchase the correct size for your home’s needs. An undersized air conditioner will have to work harder, waste energy and cost you more money. Conversely, an oversized unit will cycle too quickly and may not run long enough to remove humidity in the air.

A little homework will go a long way in ensuring you find the right size air conditioner to maximum efficiency and save money.

Here’s an easy way to determine what size air conditioner is best for your space and needs:

  1. Measure your window size.
  2. Check the power available near the window. Most larger air conditioners require a dedicated circuit and some require a 220 volt circuit.
  3. Cooling capacity is measured in British thermal units (Btus) per hour. You’ll need to calculate the number of Btus required for your space. Use the handy chart below and consider the following factors:
    • If you have high ceilings or multiple windows in your space, you’ll need to increase required Btus slightly.
    • If your space is highly shaded, you can reduce the required Btus by 10 percent.
    • If there is abundant sunshine in your space, increase the required Btus by 10 percent.
    • If the space includes a kitchen, add 4,000 Btus. Due to cooking, kitchens generate more heat than other rooms.
    • Add 600 Btus per person who regularly spends time in the room or space.

Here are the recommend sizes listed by square footage of the area to be cooled. All figures are based on a room with a ceiling height of eight feet.

Square footage of area to be cooled/capacity needed (Btus /HR)

100 to 150 = 5,000
150 to 250 = 6,000
250 to 300 = 7,000
300 to 350 = 8,000
350 to 400 = 9,000
400 to 450 = 10,000
450 to 550 = 12,000
550 to 700 = 14,000
700 to 1,000 = 18,000
1,200 to 1,400 = 23,000
1,400 to 1,500 = 24,000
Source: www.EnergyStar.gov

The moisture in the air condenses on the refrigerated coils and drips into the bottom pan of the air conditioner where it is picked up by the condenser fan blade and used to help cool the condenser coils. The heat which is removed from the home through the evaporator coils is conducted into a refrigerant gas and then travels through a radiator-like set of coils on the back of the unit. The condenser fan circulates outside air across the coils to cool them.