Estimating Appliance & Home Electronic Energy Use

If you're trying to decide whether to invest in a more energy-efficient appliance or you'd like to determine your electricity loads, you may want to estimate appliance energy consumption.

Formula for Estimating Energy Consumption

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

  • (Wattage × Hours Used Per Day) ÷ 1,000 = Daily Kilowatt-hour (kWh) consumption

Multiply this by the number of days you use the appliance during the year for the annual consumption in kWh per year. Note that 1 kilowatt (kW) = 1,000 Watts.

Estimating Annual Cost to Run an Appliance

Multiply the annual consumption in kWh per year (that you calculated above) by your local utility's rate per kWh consumed to calculate the annual cost to run an appliance. Note: 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.

Examples

  • Personal Computer and Monitor
    1. [(120 Watts + 150 Watts) × 4 hours/day × 365 days/year] ÷ 1,000
    2. = 394 kWh × 11 cents/kWh
    3. = $43.34/year
  • Window fan
    1. (200 Watts × 4 hours/day × 120 days/year)  ÷  1000
    2. = 96 kWh × 11 cents/kWh
    3. = $10.56/year

Wattage

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

Estimating Wattage

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. If not, find a clamp-on ammeter - an electrician's tool that clamps around one of the two wires on the appliance - to measure the current flowing through it. You can obtain this type of ammeter in stores that sell electrical and electronic equipment. Take a reading while the device is running; this is the actual amount of current being used at that instant.

When measuring the current drawn by a motor, note that the meter will show about three times more current in the first second that the motor starts than when it is running smoothly.

Phantom Loads

Many appliances continue to draw a small amount of stand-by power when they are switched "off." These "phantom loads" occur in most appliances that use electricity, such as 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 Wattage of Various Appliances

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

  • Aquarium - 50 to 1210 Watts
  • Clock radio - 10 Watts
  • Coffee maker - 900 to 1200 Watts
  • Clothes washer - 350 to 500 Watts
  • Clothes dryer - 1800 to 5000 Watts
  • Dishwasher - 1200 to 2400 Watts (using the drying feature greatly increases energy consumption)
  • Dehumidifier - 785 Watts
  • DVD Player - 20 to 25 Watts
  • Electric blanket:
    • Single - 60 Watts
    • Double - 100 Watts
  • Fans:
    • Ceiling Fan - 65 to 175 Watts
    • Furnace - 750 Watts
    • Whole House - 240 to 750 Watts
    • Window Fans - 55 to 250 Watts
  • Hair dryer - 1200 to 1875 Watts
  • Heater (portable) - 750 to 1500 Watts
  • Clothes iron - 1000 to 1800 Watts
  • Microwave oven - 750 to 1100 Watts
  • Personal computer:
    • Computer Tower - 120  Watts when awake, 30 or less  Watts when asleep
    • Monitor - 150  Watts when awake, 30 or less  Watts when asleep
  • Laptop - 50 Watts
  • Radio (stereo) - 70 to 400 Watts
  • Refrigerator (frost-free, 16 cubic feet) - 725 Watts
  • Televisions:
    • 19 inch - 65 to 110 Watts
    • 27 inch - 113 Watts
    • 36 inch - 133 Watts
    • 53 to 61 inch Projection -  170 Watts
    • Flat screen - 120 Watts
  • Toaster - 800 to 1400 Watts
  • Toaster oven - 1225 Watts
  • VCR Player - 17 to 21 Watts
  • Vacuum cleaner - 1000 to 1440 Watts
  • Water heater (40 gallon) - 4500 to 5500 Watts
  • Water pump (deep well) - 250 to 1100 Watts
  • Water bed (with heater, no cover) - 120 to 380 Watts