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Estimating Your Appliances’ Energy Consumption

May 9, 2014

While it’s become almost common knowledge now that many home appliances and electronics are guilty of helping drive up your energy bill if they’re not energy efficient models, it’s interesting to know how much energy they’re consuming. Fortunately, there’s a formula you can use to estimate your appliances’ energy consumption.

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

1 kilowatt (kW) = 1,000 Watts

When you multiply this by the number of days that the appliance is used over the course of one year, you’ll get the figure for the annual consumption in kWh per year.

Estimating the Annual Cost of Running an Appliance

It’s also interesting to get an idea of how much it’s costing you to run an appliance. Again, you can calculate this by multiplying the annual consumption in kWh per year (as calculated above) by your local utility’s rate per kWh consumed. This will give you an estimate of how much it’s costing you to run that appliance.

Some Examples:

Window fan:
(200 Watts × 4 hours/day × 120 days/year)  ÷ 1000
= 96 kWh × 11 cents/kWh = $10.56/year

Personal Computer and Monitor:
[(120 Watts + 150 Watts) × 4 hours/day × 365 days/year] ÷ 1000
= 394 kWh × 11 cents/kWh = $43.34/year

Because refrigerators are turned “on” all the time, in order to calculate the hours at which it operates at its maximum wattage, you need to divide the total time the refrigerator is plugged in by three. This is because although refrigerators are always on, they actually cycle on and off as needed to maintain the interior cooling temperatures.

Calculating Wattage

For most appliances, you can normally find the wattage either on the bottom or back, or in the nameplate. Keep in mind, though, it’s usually the maximum power that’s listed. Many appliances, however, have a range of settings that use different amounts of power (think volume on your radio: lower the volume, the less power used), so that actual amount of power being used will vary according to the setting.

If for whatever reason the wattage isn’t listed on the appliance, you can estimate it by using the following formula:

Current draw (in amperes) multiplied by the voltage used by the appliance.

Most U.S. appliances use 120 volts. Larger appliances though, such as clothes dryers and stoves, will use 240 volts unless otherwise specified. You can generally find the amperes stamped on the unit in place of the wattage. If the amperes aren’t listed, use a clamp-on ammeter (a tool used by electricians that clamps on one of the two wires on the appliance) to measure the current. You should take the reading immediately, while the appliance is running in order to get the actual amount of current that’s being used at that point. If you’re measuring the current being drawn by a motor, keep in mind that you’ll get a reading showing three times more current being drawn in the first second of the motor starting than when it’s running smoothly.

Some Typical Wattages of Appliances

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

While having a general idea about your appliances’ energy consumption is a good beginning, you should contact a certified RESNET Home Energy Auditor for an energy audit if you’re serious about lowering your utility bills and saving energy.

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