Recommended Sizes for Central Air Conditioners for a House

BTUs and Tons

• When you hear the word "size" in reference to a central air conditioning unit, it doesn't only mean the physical size. What the term is referring to is the BTUs or tons of cooling capacity of a particular system. BTU stands for British Thermal Unit, and it is a standard that equals the amount of energy to raise the temperature of one pound of water by one degree Fahrenheit. A ton is equal to 12,000 BTU, or the amount of energy needed to melt one ton of ice in one day. It sounds odd, but these are the standards the industry uses. Average central air conditioners are between three and six tons or 36,000 to 72,000 BTUs.

Factors to Consider

• There is no universal answer to what size air conditioner you need for a house. Each house has its own specific needs, and there are several factors that determine the ideal size of a central air conditioner for a particular location. According to the U.S. Department of Energy, the factors include the size and shape of the house, which direction it faces, how well it is insulated, the number and location of windows, number of occupants, comfort preferences and the amount of heat the interior lights produce.

Too Small

• You may be wondering about the consequences of installing the wrong-sized air conditioner for your home. It depends on if it is too small or too big. If the unit is too small, you will see an increase in energy bills because the power of the central air conditioner will struggle to keep up with the demands of the home. The more the unit has to run to maintain temperatures, the more energy that will be used. When the air conditioner is too small it may need to run for several extra hours per day.

Too Big

• If the air conditioner is too big for your house, the central unit will turn on and off much more often, causing more wear and tear on your system and shortening its lifespan. The air will also feel less comfortable, because the system will achieve the temperatures too quickly without taking the time to remove the humidity from the air. This is a major factor in air comfort. The temperatures across the entire home will also likely be less consistent.