How to Size Central Air Conditioning for a Home

Properly sizing your central air conditioner is very important to minimize your energy bills and to maximize the lifespan of your central air conditioner. An AC unit that is too small will break down sooner. An AC unit that is too large will run up your energy costs. When sizing your central air conditioner, consider your home's size, how sunlight or shade affects the rooms and how the rooms will be used.

Central AC replaces the need for room AC units.
  1. Look up the number of square feet you expect your central AC unit to cool by checking your home's blueprints. If you cannot find the blueprints and do not know the square footage, you can calculate it by measuring the dimensions of each room and hallway, calculating the areas and then adding up the total.

  2. Use a sizing chart (see resources) to find the base number of Btu you need for your home. For example, if your house is 2,200 square feet, you would need about 28,500 Btu.

  3. Count the number of well-shaded rooms and multiply the result by 1,000 Btu. Then subtract the result from the base Btu in step 2.

  4. Count the number of rooms that are on the sunny side of the home and get significant sunlight and multiply that number by 1,500 Btu. Add this result to the base Btu from step 2.

  5. Modify the estimate in step 2 if your home is not fully insulated. Each room that is not insulated adds 4,000 Btu to the base Btu amount from step 2.

  6. Add 4,000 Btu to the base Btu total for each kitchen you have in your home. The additional heat created in kitchens results in a higher cooling demand.

  7. Determine if any of the rooms in the home will have more than two people occupying it on a regular basis. If so, add 600 Btu for each person beyond the second that will be in the room. For example, if three people will share a bedroom, you would add 600 Btu.


  • Consult an HVAC professional before installing a new central air conditioning unit. Your home's needs may be different from the numbers calculated in this article because of superior or inferior duct work and insulation in your home or because of the climate that you live in.