BTUs per hour is a standard measurement that indications how many British Thermal Units an air conditioner removes from a room in one hour. A BTU is the unit of heat necessary to raise 1 pound of water by 1 degree Fahrenheit.
The BTUs per hour measurement is used in calculating efficiency ratings. Room air conditioner efficiency is measured with an EER, or Energy Efficiency Ratio. Divide BTUs per hour by the wattage used by the air conditioner unit to get the EER. The Seasonal Energy Efficiency Ratio, SEER, is calculated with the same formula. Due to improved national appliance standards, room conditioners must carry an 8.0 or greater EER and central air conditioners must carry an SEER of 9.7 or higher.