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Do the math to learn about energy consumption

Whether you’re trying to decide if a new appliance is more energy-efficient than the one humming away in your home now, or just trying to determine where to save energy, you may want to estimate the energy consumption of your appliances.


There’s a simple formula to estimate an appliance’s energy consumption – and how much it’s costing you to operate each year. Here’s how.

Use this formula to estimate an appliance’s energy use:

  1. (wattage × hours used per day) ÷ 1,000 = daily kilowatt-hour (KWH) consumption
  2. Multiply this by the number of days you use the appliance during the year for the annual consumption in KWH per year.

To estimate the annual cost to operate an appliance:

  1. Multiply the annual consumption in KWH per year (that you calculated above) by Burke-Divide Electric’s rate per KWH to calculate the annual cost to operate an appliance.
  2. 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.

Personal computer and monitor:
[(120 watts + 150 watts) × 4 hours/day × 365 days/year] ÷ 1,000= 394 kWh × 6.5 cents/kWh= $25.61/year


You can usually find the wattage of most appliances stamped on the bottom or back of the appliance, or on the nameplate. The wattage listed is the maximum power drawn by the appliance. Since many appliances have a range of settings, the actual amount of power consumed depends on the setting used at any one time.


If the wattage is not listed on the appliance, you can still estimate it by finding the 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.


Many appliances continue to draw a small amount of power when they are switched “off.” These “phantom loads” occur in most appliances that use electricity, such as DVD players, televisions, stereos, computers and kitchen appliances.


Most phantom loads will increase the appliance’s energy consumption a few watt-hours. These loads can be avoided by unplugging the appliance or using a power strip and using the switch on the power strip to cut all power to the appliance.


Typical wattages
Here are some examples of the range of nameplate wattages for various household appliances:

Clock radio = 10
Clothes washer = 350–500
Clothes dryer = 1,800–5,000
Dishwasher = 1,200–2,400 (using the drying feature greatly increases energy consumption)
Dehumidifer = 785
Ceiling fan = 65–175
Hair dryer = 1,200–1,875
Heater (portable) = 750–1,500
Clothes iron = 1,000–1,800
Microwave oven = 750–1,100
Laptop computer = 50
Radio = 70–400
Refrigerator (frost-free, 16 cubic feet)= 725
Televisions (36-inch) = 133
Flat-screen TV = 120
Toaster = 800–1,400
Toaster oven = 1,225
Vacuum cleaner = 1,000–1,440
Water heater (40-gallon)= 4,500–5,500
Water pump (deep well) = 250–1,100


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