Determining how powerful an air conditioner you need is the most important part of shopping for a new cooling system. Too weak an appliance and you'll never reach the desired temperature, while an overly strong air conditioner will short-cycle and waste energy. Finding the BTUs needed per cubic foot of your room or home will put you on the fast track to cooling success.
British Thermal Units
BTU is an abbreviation for British Thermal Unit, a measurement of heat commonly used to rate the cooling capacity of air conditioners. One BTU is roughly equal to the heat put off by a kitchen match. An air conditioner's BTU rating is the amount of heat it is capable of extracting from the air over the course of an hour; running a 1,000 BTU air conditioner for 60 minutes is the equivalent of extinguishing a thousand matches.
Default Requirements Per Cubic Foot
According to the U.S. Department of Energy, the average home has a cooling requirement of 20 BTUs per square foot. Given a default ceiling height of 8 feet, this would result in an hourly rating requirement of 2.5 BTUs per cubic foot. Note that this is very rough estimate of an average house's cooling needs. Many other factors play a significant role in determining the air conditioner strength required.
Room volume is only one of many elements that affects the cooling requirements of a living area. The quality of insulation used, window size and cardinal orientation all influence the amount of environmental heat that can enter from outside, while the average occupancy and presence of lighting and kitchen appliances all are indicative of the amount of heat generated inside.
How to Calculate Requirements
Calculating your exact BTU requirements by hand can be very complex. You can use any of the numerous online tools available to help you, all of which handle the mathematical portion of the process and leave only the data gathering up to you. Consumer Reports' calculator is one of the most comprehensive, while simpler tools such as those provided by Good Housekeeping allow you to get results quicker. All online calculators return the total BTU requirements of your living area, so divide the number by your volume to see the recommended BTUs per cubic foot for your future air conditioner.