How to Calculate Power Use by an Electric Heater

Written by david robinson
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How to Calculate Power Use by an Electric Heater
Electric heaters vary in the amount of power they use. (George Doyle/Stockbyte/Getty Images)

Like all electrical appliances, heaters consume power. Electrical energy is converted into heat energy. Knowing how much power your heater uses helps you to estimate the running costs as well as the amount of heat it will produce. Calculating the power usage necessitates knowing both the appliance's wattage--or power rating--and the amount of time it is switched on. These values are inserted into a straightforward mathematical formula to calculate the power used.

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  1. 1

    Search the appliance casing for details of its wattage. For example, a heater may be described as a 2 kilowatt heater. This is the power consumption of the appliance, which is 2 kilowatts per hour. The power may be shown in either watts or kilowatts.

  2. 2

    Calculate the heater's power usage with this formula: Time (in hours) x kilowatts = power consumption in kilowatt hours. For example, to find the power usage of a 5-kilowatt heater left running for 2 hours, enter 5 into your calculator, and multiply by 2. The answer is the power usage. In this example it is 10 kWh.

  3. 3

    Check your calculations for errors. Divide the power usage by the length of time the appliance is switched on. The result will be the power rating of the heater in kilowatts. If your answer is different, there was an error in your calculations.

Tips and warnings

  • Many heaters are marketed in terms of their power. A 9-kilowatt heater will use 9 kilowatts per hour on full power. At half power it will use 4.5 kilowatts per hour.
  • Electricity can cause injury or death. If in doubt, consult a qualified electrician when handling heaters.

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