Calculating your Electricity Use

There are several reasons why you might want to calculate your home electricity use. Reducing consumption starts with knowing how much you’re using, which appliances are the biggest draw and how you can operate your appliances more efficiently. Also, if you’re trying to decide whether to invest in a more energy-efficient appliance, you may want to estimate appliance energy consumption.
The formula for estimating an appliance’s energy use is as follows:

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

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

If you 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.

Here are 2 examples:

Window fan:

(200 Watts × 4 hours/day × 120 days/year) ÷ 1000
= 96 kWh × 8.5 cents/kWh
= $8.16/year

Personal Computer and Monitor:

(120 + 150 Watts × 4 hours/day × 365 days/year) ÷ 1000
= 394 kWh × 8.5 cents/kWh
= $33.51/year

You’ll find the wattage of your appliance or device either on the packaging or stamped on the appliance itself. 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. Most appliances in the United States use 120 volts. Larger appliances, such as clothes dryers and electric cook tops, 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.

When measuring electricity use, remember that many appliances continue to draw a small amount of power even 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 or using a power strip and using the switch on the power strip to cut all power to the appliance.

The U.S. Department of Energy offers a lot of information about appliance energy use, including comparisons of different appliances. Click here to learn more.

If you want to reduce your energy bills, consider ways that you can reduce your electricity use in the home. Calculating the energy consumption of your appliances is a good first step. Contact us for options with high efficiency air conditioning systems, too.

Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems).For more information about Indoor Air Quality and other HVAC topics,click here to visit our website.