Many appliances still list their specifications in terms of British thermal units (BTUs) per hour, a traditional unit of power. A BTU per hour is the energy required to raise the temperature of a pound of water one degree Fahrenheit over the course of one hour. The metric system, however, computes energy in terms of watts. A watt is the rate of power for a circuit where one volt of electromotive force drives one ampere of current.

Multiply the number of BTUs the appliance moves per hour by 1,055, which is the number of joules in one BTU. For instance, if a unit moves 24,000 BTUs each hour, calculate 24,000 x 1,055 = 25,320,000 joules per hour.

Divide this answer by 3,600, which is the number of seconds in an hour. So you would calculate 25,320,000 / 3,600 = 7,033.33 joules per second = 7,033.33 watts.

Divide the amount in Step 2 by 1,000 to convert it to kilowatts if the result is greater than a thousand. In the example, you would have 7,033.33 / 1,000 = approximately 7 kilowatts.
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