The Size for a Central Air Conditioner by Square Footage

AC Size Facts

• The size of an air conditioner actually has nothing to do with its physical dimensions. Not really. When someone speaks about an air conditioner’s size, they typically mean the amount of BTUs the unit is capable of putting out. BTUs are the common term for British Thermal Units. One BTU is equivalent to the amount of energy needed to raise the temperature of 1 pound of water by 1 degree Fahrenheit. This term may sound more appropriate for heating, but the energy standard also applies to cooling. The term will tell the buyer how much the air conditioner can cool in a given amount of time -- an important factor in determining the proper size.

Square Foot Rule

• A rule of thumb can point you in the right direction when you get ready to choose your unit. For every 500 square feet of floor space you need to cool, you will need 1 ton of cooling power per hour. One ton is the equivalent of 12,000 BTUs per hour. If you have a 2,500-square-foot house, you can assume that with no other factors considered, it will take a 5-ton unit to cool your home.

Additional Heat Factors

• You may have to add some air conditioning power for additional heat factors. Assume that you need an extra 380 BTUs to cool an area inhabited by one person and an additional 380 for each person living in the home because of the heat the human body adds to the room. You should also factor in 1,200 BTUs for every area in the home where cooking takes place. The kitchen adds a significant amount of heat to a home.

Manual J

• The Manual J method is the accepted professional method for calculating air conditioner size. The method takes square footage into account but also involves the climate where the house is located, the number of windows, which direction they face and the quality of insulation.

Problems With Improper Size

• Selecting the right air conditioner is important for comfort and energy costs. If your air conditioner is too small, it will have to work constantly in warm weather to maintain a comfortable environment for you and your family. This also raises your electric bill. On the other hand, if the air conditioner is too large, it may cool the air too quickly and fail to remove the needed moisture from the home, which affects comfort levels.