Air Conditioner Cooling Load Calculation

Why Cooling Load Matters

• Choosing a model to handle the room's cooling load is vital when purchasing a new air conditioner. The cooling load determines how powerful the air conditioner needs be to keep the room at a comfortable temperature. If the air conditioner is too weak, the unit may not cool the room down sufficiently; however, buying an AC unit that is too powerful can be equally undesirable, by wasting energy and leaving the air damp and clammy.

Measuring the Cooling Load

• Cooling loads are measured in British Thermal Units (BTUs). One BTU is roughly the equivalent of the warmth from a kitchen match. In more exact terms, one BTU is the amount of heat it takes to raise the temperature of a pint of water by one degree Fahrenheit. A room's air conditioner cooling load is the amount of heat that must be extracted from it hourly to keep it at the desired temperature.

Standard Guidelines

• The U.S. Department Of Energy recommends a cooling load of 20 BTUs per square foot, though other factors also affect the required cooling capacity. Bright sunlight adds 10 percent, and heavy shade takes away 10 percent from the cooling load; additionally, more than two occupants adds 600 BTUs to the room's needs per person, and kitchen appliances add an additional 4,000 BTUs.

Online Calculators

• If you need more precise calculations, you can use one of the numerous online BTU calculators available. The worksheet provided by Consumer Reports uses a wide range of factors to provide you with precise results while Good Housekeeping's AC-sizing tool is a simpler calculator designed for quick results.