Estimate your home energy usage

Knowing the amount of energy consumed by each appliance or device in your home provides an idea of how to modify energy usage, and as a result, can lead to reduced monthly energy bills. With a little bit of math and a calculator, a home’s energy usage and savings can be estimated. Using an electricity usage monitor can even estimate these with little effort.

Before any math is done, you must first know the wattage of your appliances. This can be found on the nameplate, or stamped on the bottom or back of an appliance. The wattage listed is the maximum power drawn. Since many appliances have a range of settings (for example, the volume on a television or speed settings on a fan), the actual amount of power consumed varies upon the settings used at any one time. If an appliance’s wattage cannot be found, this convenient table (opens new page, linked to where table below is located) contains a list of typical wattage ranges for most appliances around the home.

To begin, take the wattage and multiply it by the hours the appliance is estimated to be used each day. Divide this number by 1,000. This is an appliance’s kilowatt hour (kWh) usage each day.

Next, multiply your utility’s rate per kWh by the daily kWh usage determined above. Alternatively, if the rate for a utility provider is unknown, the average for South Dakota is 9.35 cents per kWh. This total is the cost to run the appliance each day.

To determine the usage for a month or year, just multiply the days of estimated use during that time period. The resulting number will be the cost (in cents) to run an appliance during that month or year.

Below is a formula that illustrates how to determine the cost for an appliance for a month or year.

one kilowatt (kW) = 1,000 Watts

Note: For refrigerators, divide the total hours used by three. Refrigerators, although continuously running, actually cycle on and off, as needed, to maintain interior temperatures.

Examples:

Clothes washer, annual usage:

(450 Watts × 4 hours/day × 52 days/year x 9.35 cents/kWh) ÷ 1000 = $8.75/year

36-inch television, monthly usage:

(133 Watts × 6 hours/day × 30 days/month x 9.35 cents/kWh) ÷ 1000 = $2.24/month

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Once a list of estimated appliance energy usages has been determined, it is time to put that information to work. Some questions that should be asked when looking at the annual cost to run these appliances are:

  • Which of these are the most energy-intensive?
  • What can be done to reduce the amount of energy used?
  • Can the usage of these appliances be modified to make them more energy-efficient?
  • Can other appliances perform just as well while using less energy?
  • Would it be a good time to replace an older appliance with a newer, more efficient model?

Typical Appliance Wattage Ranges

What to expect when purchasing new appliances

Some information provided by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy and the U.S. Environmental Protection Agency.