Appliance Energy Cost
What your appliances cost to run, and whether a more efficient one pays for itself.
Cost per year
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Cost per year by appliance
How this is calculated
Energy (kWh/yr) = watts × hours per day × days per year ÷ 1000
Standby (kWh/yr) = standby watts × (8,760 − hours on per year) ÷ 1000
Cost per year = (energy + standby) × price per kWh × how many
Per month = per year ÷ 12 Per day = per year ÷ 365
Watts = amps × volts
Payback (years) = cost of replacement ÷ yearly saving
This is the method the US Department of Energy gives for estimating appliance use. A kilowatt-hour (kWh) is 1,000 watts for one hour, the unit your bill uses. Standby power is what a device draws while plugged in and switched off or idle; it is counted for every hour of the year the device is not in use.
Getting good numbers
- The wattage is usually on a label on the back or bottom, or in the manual. A plug-in energy meter gives the real figure.
- Labels often show the maximum power. Many devices use less most of the time, so a label-based estimate can be on the high side.
- Refrigerators, freezers, heaters and air conditioners switch on and off by themselves. Enter the hours they actually run, not 24. For a fridge, the yearly kWh on its energy label is the best guide.
- Amps × volts is exact for heaters and kettles. For motors and electronics it is an upper limit.
What this leaves out
A single flat price per kWh is used. If your tariff changes by time of day, by season or by how much you use, use the rate that applies when the appliance runs. Fixed daily charges on your bill do not change with use and are not included. Payback is simple payback: no interest, no price changes.