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Estimating appliance and home electronic energy use.


Determining how much electricity your appliances and home electronics use can help you understand how much money you are spending to use them. 

Follow these steps for finding the annual energy consumption of a product, as well as the cost to operate it.

Estimate the number of hours per day an appliance runs. There are two ways to do this:

Rough estimate
If you know about how much you use an appliance every day, you can roughly estimate the number of hours it runs. For example, if you know you normally watch about 4 hours of television every day, you can use that number. If you know you run your whole house fan 4 hours every night before shutting it off, you can use that number. To estimate the number of hours that a refrigerator actually operates at its maximum wattage, divide the total time the refrigerator is plugged in by three. Refrigerators, although turned “on” all the time, actually cycle on and off as needed to maintain interior temperatures.

Keep a log
It may be practical for you to keep a usage log for some appliances. For example, you could record the cooking time each time you use your microwave, work on your computer, watch your television, or leave a light on in a room or outdoors.

Find the wattage of the product. There are three ways to find the wattage an appliance uses:

Stamped on the appliance
The wattage of most appliances is usually stamped on the bottom or back of the appliance, or on its nameplate. The wattage listed is the maximum power drawn by the appliance. Many appliances have a range of settings, so the actual amount of power an appliance may consume depends on the setting being used. For example, a radio set at high volume uses more power than one set at low volume. A fan set at a higher speed uses more power than one set at a lower speed.

Multiply the appliance ampere usage by the appliance voltage usage
If the wattage is not listed on the appliance, you can still estimate it by finding the electrical current draw (in amperes) and multiplying that by the voltage used by the appliance. Most appliances in the United States use 120 volts. Larger appliances, such as clothes dryers and electric cooktops, use 240 volts. The amperes might be stamped on the unit in place of the wattage, or listed in the owner’s manual or specification sheet.

Use online sources to find typical wattages or the wattage of specific products you are considering purchasing. The following links are good options:

The Home Energy Saver provides a list of appliances with their estimated wattage and their annual energy use, along with other characteristics (including annual energy use, based on “typical” usage patterns. Continue using the equations here if you want to find energy use based on your own usage patterns).

ENERGY STAR offers energy-use information on specific products that have earned the ENERGY STAR. The information varies across products, but if you are considering purchasing a new, efficient product, ENERGY STAR allows you to select and compare specific models. In some cases, you can use the provided information to do your own estimates using the equations here. The information may also help you compare your current appliances with more efficient models, so you understand potential savings from upgrading to a more efficient appliance.

Find the daily energy consumption using the following formula:

(Wattage × Hours Used Per Day) ÷ 1000 = Daily Kilowatt-hour (kWh) consumption

Find the annual energy consumption using the following formula:

Daily kWh consumption × number of days used per year = annual energy consumption

Find the annual cost to run the appliance using the following formula:

Annual energy consumption × utility rate per kWh = annual cost to run appliance