- Measure the area in square feet of the room the air conditioner will cool. Multiply the length of the room by the width to get the area. As an example, a 12-foot by 10-foot room is 120 square feet.
- Determine the BTUs needed for the measured area. A 100- to 200-square-foot room will require an air conditioner in the 7,000 to 10,000 BTU range. A 250- to 350-square-foot room will require an air conditioner in the 9,000 to 12,000 BTU range. A 350- to 450-square-foot room will require an air conditioner in the 12,000 to 16,000 BTU range.
- Reduce your BTU calculation by 10 percent if the room is shaded by trees or buildings. Increase the BTU calculation by 10 percent if the room is always sunny or is on the second floor.
- Increase your BTU calculation by 600 BTU if more than two people usually will be in the room at the same time.
- Add 4000 BTU to any air conditioner that is going to placed in the kitchen.
- Running an air conditioner for any length of time means using more power. Select a high Energy Efficiency Rating (EER) to reduce power consumption.
Things You Will Need
- Tape measure
- Central air conditioners are rated by the ton of cooling capacity. One ton is the equivalent of 12,000 BTU.