The electric kettle wins the final round of #EnergyFaceoff. | Graphic by Stacy Buchanan, National Renewable Energy Laboratory
Residential microwaves vary in their wattages; the higher the wattage, the faster your food or liquid generally cooks. For this Energy War, we used two products we had available to compare the energy use: a 1,000 watt (W) microwave and a 1,500 W electric kettle.
Looking at just the wattages, you might think that the microwave would be more efficient. But what we found is that the time to heat the water makes all the difference.
For our test, we heated an eight ounce cup of water and timed how long it took each. For the microwave, we used the "Beverage" setting, and it took about four minutes to heat the cup of water. The kettle took 1:30 to heat the same amount of water. So not only are you saving precious minutes, you're also saving energy!
Assuming someone might do this three times a day, five days a week, we followed the steps for calculating annual energy use and cost on Energy Saver (note that we used weekly energy consumption instead of daily):
Time used: 4:00, 3 times per day, 5 days a week. (1 hour per week)
Wattage: 1000 W
(1,000 W x 1 hour) / 1000 = 1 kWh/week (weekly energy consumption)
1 kWh/week x 52 weeks = 52 kWh (annual energy consumption)
52 kWh x $0.11 = $5.72 per year
Time used: 1:30, 3 times per day, 5 days a week (.375 hours per week)
Wattage: 1500 W
(1,500 W x .375) / 1000 = .56 kWh/week (weekly energy consumption)
.56 kWh/week x 52 weeks = 29.12 kWh (annual energy consumption)
29.12 kWh x $0.11 = $3.20 per year
Those aren't enormous savings, but if you find yourself boiling water a lot (or if you're in an office with a lot of tea drinkers), they can add up. One thing to also consider is that you are more likely to heat the exact amount of water you need in the microwave, whereas you might overfill the electric kettle and negate your savings with a longer time to boil (so just heat what you need!).
Do you use an electric kettle? Try this test with your own kettle and microwave and let us know your results (be sure to share the wattages and the time it took each to heat the water).