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Estimating Your Appliance Costs  

 
 
 



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. To calculate energy usage use the appliance cost formula below or visit our
cent a meter page for more information. The amount of electricity you use is measured in kilowatt hours (kWh). One kWh (also termed 'a unit' of electricity) is simply the equivalent of 1000 watts used for a period of one hour.

The running cost of an appliance depends on the wattage the appliance operates at and the length of time it is used. For example: a 1000 watt iron takes one hour to use one kWh, while a 500 watt vacuum cleaner takes two hours to use one kWh.

Formula for Estimating Energy Consumption

You can use this formula to estimate an appliance's energy use:

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

(1 kilowatt (kW) = 1,000 Watts)

Multiply this by the number of days you use the appliance during the year for the annual consumption. You can then calculate the annual cost to run an appliance by multiplying the kWh per year by your local utility's rate per kWh consumed.

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:

Incandescent Light Bulb:

( 100 Watts x 8 hours /day x 365 days/year)   ÷ 1000
= 292 kWh x .18 cents/kWh
=$52.56/year

Energy Saving Light Bulb:
(20 Watts x 8 hours/day x 365 days/year)  
÷ 1000
=58.4 kWh x .18 cents/kWh
=$10.51year

Window fan:

(200 Watts x 4 hours/day x 120 days/year)  ÷  1000
= 96 kWh x .18 cents/kWh
= $17.28/year

Personal Computer and Monitor:

(120 + 150 Watts x 4 hours/day x 365 days/year)  ÷  1000
= 394 kWh x .18 cents/kWh
= $70.92/year

Note: cents per/kWh will depend on what your electricity provider will be charging - 18 cents is used as an example. You can find this information on the back of  your electrical account or contact your electrical provider. Some electrical providers can charge up to 20 cents per kWh.

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.

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, appliances in  Australia 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.

Convert Amps to Watts Formula

The following formula will calculate the watts from amps, find the total amps on the name plate of your appliance.

Convert amps to watts

Watts = voltage x amps:
p = E x I
E = Voltage / I = Amps /W = Watts /P = Power

Example:

10 amps multiplied by 240 volts = 2400 watts.
( for 3 phase appliances multiply 1.73)

For 208 volts x 1.732, use 360
For 230 volts x 1.732, use 398
For 240 volts x 1.732, use 416
For 440 volts x 1.732, use 762
For 460 volts x 1.732, use 797
For 480 Volts x 1.732, use 831

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.

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 VCRs, 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.

Convert Watts to To Amps Formula

Amps = Watts / Voltage
I = P ÷ V

Example:

Convert 2800 watts to amps  = 2800 w divided By 240 volts = 11.66 Amps.
If you have a KW unit  - 2.8KW  simply multiply 2.8 by 1000 = 2800 and use the above formula.

(for 3 Phase divide by 1.73)

Typical Wattages of Various Appliances

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

   Aquarium = 50 - 1210 watts
   Clock radio = 10
   Coffee maker = 900 - 1200
   Clothes washer = 350 - 500
   Clothes dryer = 1800 - 5000
   Dishwasher = 1200 - 2400 (using the drying feature greatly increases energy consumption)
   Dehumidifier = 785
   Electric blanket- Single/Double = 60 / 100
   Fans Ceiling = 65 - 175watts , Window = 55 - 250 watts
   Furnace = 750
   Whole house = 240 - 750
   Hair dryer = 1200 - 1875
   Heater (portable) = 750 - 1500
   Clothes iron = 1000 - 1800
   Microwave oven = 750 - 1100 watts
   Personal computer CPU - awake / asleep = 120 / 30 or less Monitor - awake / asleep = 150 / 30 or less Laptop = 50img
   Radio (stereo) = 70 - 400
   Refrigerator (frost-free, 16 cubic feet) = 725
   Televisions (color) 19" = 65 - 110 watts , 27" = 113 watts , 36"= 133watts,  53"-61" Projection = 170watts,  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 watts

 

If your account costs has increased it is likely to be the result of:

  • A longer than normal billing period.
  • Increased usage of energy.
  • An increase in energy costs may have occurred that you are not aware of.
  • An estimate of your account has been made due to an inability to read your meter (i.e.: due to locked meter box, etc.)
  • Meter has been incorrectly read. How to read your Meter - How To Read Your Electricity Meter
    In a few cases, your energy consumption cost may have changed, due to the meter being faulty. If this is the case, your Power  retailer will test the meters for a fee. If the meter is faulty, your Power retailer will replace it with a new meter and reimburse the fee.