To stay cool and keep your home maintenance costs to a minimum, you need to accurately size your central air conditioning system. If it's too large, it will frequently cycle on and off, increasing your electric bill and adding wear and tear on your central AC system. If it is too small, the system will be overworked and may break down. The size of a central air conditioning system is measured in British thermal units (BTU) or tons. Each ton equals 12,000 BTU.
Determine the square footage of your home. Most home blueprints list the total amount, but you can also measure each room and add the total.
Determine the approximate number of BTU you need for your central air conditioning system by using a sizing chart, which can be found online. For example, a 1,700 square foot home would need about 25,500 BTU, or just over 2 tons.
Consider the sunlight each room in your house receives. For each room that gets significant sunlight, calculate the BTU required for that room and add 10 percent. For example, a 200 square foot room requires about 6,000 BTU, so if it received significant sunlight, you would add 600 to the estimate. For each room that is shaded, subtract 1,000 BTU from the estimate.
Consider the layout of your home to adjust the estimate. Each room used as a kitchen requires an additional 4,000 BTU. Each room that is above a kitchen needs another 1,500 BTU.
Consider the construction of your home. For each room that is not insulated, add 4,000 BTU.