How to Measure BTU Output

Written by robert vaux
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BTU stands for British Thermal Units, a means of measuring heat and energy. One BTU equals the amount of energy required to heat one pound of water by 1 degree Fahrenheit. The BTU output measures how much heat or other energy a given appliance is generating --- very useful when determining if a unit can heat a given space.

Skill level:


  1. 1

    Locate the voltage (in volts), current (in amps) and/or wattage (in watts) of the device you wish to measure. The instruction manual of the unit or a label on the device itself should list these measurements.

  2. 2

    Calculate the wattage of the device by multiplying the volts by the amps. For example, if the device has a voltage of 160 volts and a current of 2 amps, its wattage would be 320 watts (160 times 2).

  3. 3

    Divide the result by 3.413 --- a constant figure --- to determine the BTUs per hour. To cite the example in Step 2, divide the 320 watts by 3.413 to get 93.76 BTUs per hour.

  4. 4

    Multiply the BTUs per hour by the number of hours the device runs to determine its total BTU output. To continue the example, if the device runs for 4 hours, it will generate 375.04 BTUs in that period of time (93.76 BTU/hour times 4 hours).

Tips and warnings

  • Inefficient heaters may generate less wattage than the paperwork suggests. If you know the device is not generating the amount of BTUs you calculate that it should, take it to a repair shop or purchase a new one.

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