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.
Incandescent Light Bulb:
( 100 Watts x 8 hours /day x 365 days/year) ÷ 1000
= 292 kWh x .18 cents/kWh
Energy Saving Light Bulb:
(20 Watts x 8 hours/day x 365 days/year) ÷ 1000
=58.4 kWh x .18 cents/kWh
(200 Watts x 4 hours/day x 120 days/year) ÷ 1000
= 96 kWh x .18 cents/kWh
Personal Computer and Monitor:
(120 + 150 Watts x 4 hours/day x 365 days/year) ÷ 1000
= 394 kWh x .18 cents/kWh
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.
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
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.
Amps = Watts / Voltage
I = P ÷ V
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.