British Thermal Unit (BTU)

A unit of heat energy. In HVAC, a British thermal unit (BTU) measures heating or cooling capacity: one BTU is the amount of heat needed to raise one pound of water by one degree Fahrenheit. Cooling/heating capacities are often given in BTU/hour. For example, a 1-ton AC unit can remove 12,000 BTUs per hour, since one ton equals 12,000 BTU/h.