The proper size of an air conditioner needed for a house depends on the square footage of the home. For example; a 1,000-square-foot home requires an 18,000 BTU air conditioner, whereas a 34,000 BTU air conditioner is the perfect size for a 2,000-square-foot home.
To determine the square footage of an entire home, or the area to be cooled, multiply the length of the area by the width. The resulting number is the square footage that can then be used to determine the recommended air conditioner size. Energy Star provides an excellent chart to help establish the correct size of air conditioner required based on the square footage of a house.