BTU/hour is aunit of power, measuring energy per unit time, equal to 1 BTU being output in an hour. Although the watt is the largely accepted unit for power in places that use the SI system, the BTU/hour measure is still commonly used to describe the power output of many industrial applications including steam generators, home heating (like furnaces), and air conditioning.

The BTU[1] is defined as 251.9958 calories, and due to the calorie having many different accepted values,[2] the International Table (IT) value for the calorie (where 1 calorie = 4.1868 joules) is the most commonly accepted, and is the value which this encyclopedia uses.


For Further Reading


  1. Because the imperial system of units isn't as standardized as the SI, there are several different BTU units that are very closely related. See the BTU page for further explanation.
  2. American Physical Society. Energy Units [Online]. Available: