How to Calculate Your Home Energy Usage

Being able to calculate the amount of energy that appliances and devices use in your home can go a long way towards the ability to save on utility costs. Monitoring devices are available for purchase but these can be quite costly. Gathering some general information and some simple math should get you pointed in the right direction.

The math:

One kilowatt (or one Kw) equals 1000 watts.

Kilowatt per hour consumption is determined by: (wattage X hours of use) divided by 1000.

The next figure needed is your cost per kWh electric rate. As an example one current rate in Ohio is 9.7 cents per kilowatt hour.

The cost of running a 60 watt bulb for 24 hours would be: 60 watts X 24 hours = 1440. 1440 divided by 1000 = 1.44. 1.44 times 9.7 cents = 13.96 or 14 cents per day. This may not seem like much but consider that the cost is $4.20 for a month of constant use. Change that bulb to a 15 watt energy saving bulb and the monthly cost is $1.05.

If the wattage can not be determined the amount can be figured out if you know the amperage of the device and multiply that by the voltage, 120 or 240 volts. A 10 amp appliance on 120 volts uses 1200 watts per hour.

How much does it use?

Most appliances will have the wattage for the device listed near the serial number and model information plate. The wattage listed is the maximum amount of energy used by the appliance. The following figures are averages:

Clock radio = 10 watts

Coffee maker = 900 to 1200 watts

Dehumidifier = 785 watts

Hair dryer = 1200 to 1800 watts

Microwave oven = 750 to 1100 watts

Personal computer = 120 watts, 30 watts in sleep mode

Laptop computer = 50 watts

Computer monitor = 150 watts, 30 in sleep mode.

Portable heater = 750 to 1500 watts

16 cubic foot refrigerator = 725 watts for running time.

27″ TV = 113 watts

53″ projection TV = 170 watts

Electric water heater = 4500 watts for running time.

Window fan = 55 to 250 watts

Furnace fan = 750 watts

Washing machine = 350 to 500 watts

Dryer = 1800 to 5000 watts.

The personal computer that runs 24/7 with no sleep mode will cost $8.40 per month. When you add up each individual amount you can see where all the money is going.

Exceptions:

With certain items, like refrigerators that run on cycles, you will need to know the run time hours over a 24 hour period. For refrigerators the run time is considered to be 8 hours in 24. Another exception to be considered is that anything with a motor will draw more power in the first few seconds when the motor first starts.

“Phantom loads”:

Phantom loads are the power that is consumed by a device when it is not in use. Most devices are using a small amount of energy even when they are turned off. They best way to eliminate this energy use is to unplug the device or have it connected to a power strip with a shut off.

These results that you obtain from these calculations will not be exact but should be helpful in determining where you can save on utility costs. Some fairly low cost monitoring devices are also available to get exact energy consumption figures.

References:

http://www.energycircle.com/shop/kill-a-watt-ez-electricity-monitor.html

http://www1.eere.energy.gov/calculators/homes.html

http://www.energysavers.gov/your_home/appliances/index.cfm/mytopic=10040