ENERGY SERIES: Estimating Appliance and Home Electronic Energy Use

If you're trying to decide whether to invest in a more energy-efficient appliance or if you'd like to determine your electricity loads, you may want to estimate appliance energy consumption.

Estimating Energy Consumption

Use this formula to estimate an appliance's energy consumption:

(Wattage × Hours Used per Day ÷ 1000)

= Daily Kilowatt-hour (kWh) consumption (1 kilowatt (kW) = 1,000 Watts)

Multiply this by the number of days the appliance is used during the year for the annual consumption. Calculate the annual cost to run an appliance by multiplying the kWh per year by your utility's rate per kWh consumed.

Note: To estimate the number of hours that a refrigerator actually operates at its maximum wattage, divide the total time the refrigerator is plugged in by three. Refrigerators, although turned "on" all the time, actually cycle on and off as needed to maintain interior temperatures.

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

Wattage

Locate the wattage of most appliances stamped on the bottom or back of the appliance, or on its nameplate. The wattage listed is the 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 aat 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 equipment. Take a reading while the device is running; this is the actual amount of current being used at that instant. Make sure you are familiar with how to use the ammeter safely and following manufacturer’s recommendations..

When measuring the current drawn by a motor, note that the meter will show about three times more current in starting the motor than when it is running smoothly. This extra demand during starting is a motor design but could result in increases in electric rate for peak load.

Many appliances continue to draw a small amount of power 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.

Typical Wattages of Various Appliances

Here are some examples of the range of nameplate wattages for various household appliances:

• Aquarium = 50–1210 Watts
  
• Clock radio = 10
  
• Coffee maker = 900–1200
  
• Clothes washer = 350–500
  
• Clothes dryer = 1800–5000
  
• Dishwasher = 1200–2400 (using the drying feature greatly increases energy consumption)
  
• Dehumidifier = 785
  
• Electric blanket- Single/Double = 60/100
  
• Hair dryer = 1200–1875
  
• Heater (portable) = 750–1500
  
• Clothes iron = 1000–1800
• Microwave oven = 750–1100
• Fans
  • Ceiling = 65–175
  • Window = 55–250
  • Furnace = 750
  • Whole house = 240–750

• Personal computer
  • CPU - awake / asleep = 120/30 or less
  • Monitor - awake/asleep = 150/30 or less
  • Laptop = 50

• Radio (stereo) = 70–400
• Refrigerator (frost-free, 16 cubic feet) = 725
• Televisions (color) 
  • 19" = 65–110 
  • 27" = 113
  • 36" = 133
  • 53"-61" Projection = 170
  • Flat screen = 120

• Toaster = 800–1400
  
• Toaster oven = 1225
  
• VCR/DVD = 17–21 / 20–25
  
• Vacuum cleaner = 1000–1440
  
• Water heater (40 gallon) = 4500–5500
  
• Water pump (deep well) = 250–1100
  
• Water bed (with heater, no cover) = 120–380

Developed as part of the NASULGC/DOE Building Science Community of Practice. The factsheet editors are: Robert "Bobby" Grisso, Extension Engineer, Biological Systems Engineering; Martha A. Walker, Ph.D, Community Viability Specialist, Central District; and John Ignosh, Extension Specialist, Biological Systems Engineering.

DISCLAIMER – This piece is intended to give the reader only general factual information current at the time of publication. This piece is not a substitute for professional advice and should not be used for guidance or decisions related to a specific design or construction project. This piece is not intended to reflect the opinion of any of the entities, agencies or organizations identified in the materials and, if any opinions appear, are those of the individual author and should not be relied upon in any event.