Use of Electricity in Appliances
Calculating the electricity usage of your household appliances can be a useful means of identifying the least energy efficient appliances in your home, comparing the efficiency of current appliances you need to replace with that of new ones in the store, or even tracking a possible problem with your electrical meter. There are several different ways to describe and determine the energy usage of household appliances, but using a simple formula, you can understand usage in a way that can be useful in the long-term maintenance of all of your household appliances. Does this Spark an idea?
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Preparation
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The United States Department of Energy (DOE) uses a simple formula to calculate the amount of electricity an appliance uses in kilowatts over a one year period. To use this formula, you will need to know the price per kilowatt hour your utility company charges you (usually listed on your utility bill). For each appliance you measure, you will need to estimate both the number of days that you use the appliance in one year as well as the number of hours that appliance stays on while being used. Finally, inspect the appliance you are measuring to find its maximum wattage, which is nearly always printed on or etched into the surface of the appliance.
Calculation
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To put the formula together, first take the wattage listed on the appliance and multiply it by the number of hours that the appliance runs at a time (since the wattage listed on the appliance is the amount used over a one hour period). For example, say you only watch TV two hours per day and you need to measure its electricity usage. If the TV lists 113 watts as its one hour usage, multiply that by two to find that the TV uses 226 watts per day and (x 365) 82,490 watts or 82.49 kilowatts per year. If your utility provider charges 7 cents per kilowatt, you could therefore estimate that the TV costs around $5.77 per year to operate.
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Energy Usage in Perspective
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You have other important factors to consider when trying to calculate the electricity usage of your appliances. Wattage listings relate to the one-hour wattage usage on the appliance's highest possible setting, so if the appliance you are observing has more than one speed or power setting, it will likely use less wattage when set on one of these lower settings. This is a simple formula for calculating the usage of appliances that you own, but if you are more interested in the average usage of certain appliances in general, several credible sources list this information (see Resources).
Other Considerations
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Though rare, you will encounter some appliances that do not have a wattage listing on them. In this case, you can purchase an inexpensive ammeter at an electronics or hardware store and follow the manufacturer's instructions to take a reading of the current draw of an appliance while it is running and multiplying the reading by the appliance's voltage. Most household appliances use 120 volts with the only exception being clothes dryers, cook tops and other large appliances that use 240-volt electrical outlets. Since the ammeter measures an appliance's draw in real time, often using this formula can yield a more accurate wattage estimation than the one printed on the appliance itself.
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