How to Estimate the Electrical Usage for a New Building
- 1). Find the wattage of each appliance. You can often find the wattage stamped on the appliance somewhere: the back, bottom, or on the nameplate.
- 2). You can also estimate it by finding the current draw in amperes (amps). This is sometimes stamped on the appliance in place of wattage. Multiply the amps by the voltage used by the appliance to get the watts. Larger appliances, such as dryers or electric cook tops, use 240 volts. In the U.S. and Japan, most everything else uses 120 volts, but elsewhere the voltage will probably be 240.
- 3). If the appliance's current draw (amps) isn't listed on the machine, you'll need a clamp-on ammeter. Take a reading while the appliance is running and this is the actual amount of current being used at that instant. This is still measured in amps, so it needs to be multiplied by the voltage to convert it to watts.
- 4). When estimating a refrigerator's energy usage, the US Department of Energy recommends that after totaling the amount of time your refrigerator is running, divide that total by three. Although "on" all the time, refrigerators cycle on and off to maintain interior temperatures while saving energy.
- 5). When calculating for appliances which continue to draw a small amount of power when they are switched "off" (such as VCRs, stereos, televisions, computers, and microwaves) you'll need to multiply the wattage by the hours used per day, and then add about 5 watts.
- 6). Multiply each appliance's wattage by the estimated run hours, and then the estimated days per year that you use the appliance. Divide by 1,000 (so that the answer is displayed in kilowatts (kW). 1 kilowatt = 1,000 watts. This will give your annual kilowatt usage for that appliance. Add them together to get a household total.
- 7). Calculate the annual cost to run a household by multiplying the annual kilowatt usage by the local utility's rate per kilowatt-hour (kWh) consumed.
