Sizing Guideline for Air Conditioning Units

Square Footage

• To pick the proper room air conditioner, you must know the square footage of the room. Figuring out the square footage depends on the shape of a room. Finding the square footage for a square or rectangular room requires multiplying the length of the room by its width. However, determining the square footage of a triangular room requires an extra step. You must multiply the length of a room by the width, then divide by two.

Make Adjustments

• Some circumstances may affect the size of a window air conditioner. Therefore, before selecting a window air conditioner, you must make adjustments. For instance, where the air conditioner is installed makes a difference. If it's installed in a kitchen, then approximately 4,000 BTUs must be added to the capacity. Sun and shade in a room also affects the capacity. A heavily shaded room requires 10 percent decrease in capacity. However, a sunny room requires an increase of 10 percent.

Cooling Capacity

• The British Thermal Unit, commonly called BTU, describes the amount of heat required to increase 1 pound of water a degree. For example, a 10,000 BTU window air conditioner is capable of removing 10,000 BTU of heat per hour, explains the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. After determining the square footage, you must use it---in conjunction with BTUs---to find the right size air conditioner. For instance, a 400-square-foot room needs window air conditioner with the capacity of 9,000 BTUs.

Considerations

• The energy efficiency ratio measures a window air conditioner's efficiency. The ratio compares the BTUs to the wattage or power input. Thus, the higher the EER, the better the room air conditioner works. National appliance standards require a room air conditioner to have an EER ranging from 8.0 to 9.8 or higher, according to the U.S. Department of Energy.