The Science of Sustainability

2 Top Kitchen Appliance Energy Myths De-bunked

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Who's more energy efficient with the dishes– you or your dishwasher? Image: Ronan_tlvA microwave oven is the most efficient way to heat water for a cup of tea, hot chocolate, or coffee. True or False?

Now as a regular morning coffee drinker who uses a kettle and a gas stove to heat water for coffee (not instant– yuk! I use a coffee filter cone and PEET's coffee, of course) instead of the microwave, since our microwave is an old piece of inefficient junk that takes forever to heat water, I thought that buying a new microwave would make me a more energy efficient coffee drinker. But I was wrong!

Jennifer Mitchell-Jackson, while a graduate student at Lawrence Berkeley National Laboratory, measured the energy use of an average microwave oven, an electric stovetop, and a gas stovetop to heat up a mug of water. Turns out that an electric stove uses 25% less electricity than an average microwave oven to heat a mug of water. A gas stove is less efficient and uses more energy than a microwave oven, but depending on the cost of gas, it might cost less to heat a mug of coffee with gas compared to the microwave.

It is more efficient to wash dishes by hand than it is to use a dishwasher. True or false?

How many arguments has that one caused! The research to dispel this myth came from Germany. Rainer Stamminger, a professor of household and appliance technology and his colleagues at the University of Bonn, gathered more than 100 volunteer dishwashers with varying skill levels and dishwashing styles in a laboratory, and measured the amount of water and energy each used to wash big stacks of dirty dishes. He then washed similar dirty dishes in dishwashers and measured the dishwashers’ water and energy use.

His conclusion: The machine is more efficient than the hand. In general, the dishwashers used much more water and somewhat more energy than the dishwashing machines. Some test subjects used 53 gallons of water to clean 12 place settings! But there is a wide variation in the styles and economics of hand dishwashing.

Clearly, a new, efficient dishwasher is best. But if you can’t afford one, or like to spend a lot of time with your hands in soapy water, Stamminger and company have some suggestions:

  • Remove large dish scraps with a fork or spoon.
  • Do the dishes soon after a meal before the food has dried on the plates (get your dinner guests involved).
  • Do not pre-rinse your dishes under running tap water (same goes for dishwasher use).
  • Use a hot-water sink for washing and a cold-water sink for rinsing.
  • Use just the amount of detergent recommended by the manufacturer.

And put that coffee mug in the dishwasher when you're done.

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Category: Energy, Environment, Partners

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Jim Gunshinan

About the Author ()

Jim Gunshinan is the editor of Home Energy, the magazine of sustainable home building and renovation.
  • Jan Grygier

    You didn't discuss electric kettles. I suspect they are most efficient of all, since they are somewhat insulated and heat the water with an immersion element. But the semi-insulated plastic ones worry me about leaching toxins, and the manufacturers refuse to tell me which plastics they are made of – do you have any ideas on this? Of course one can always go for a stainless steel electric kettle, but those are a) uninsulated, and b) expensive.

  • http://www.homeenergy.org Jim Gunshinan

    Hi Jan,

    Thanks for your comments and adding to the discussion.

    I don't know about the plastics used in electric kettles. Given that they have to withstand a lot of heat, I'm sure many have some nasty additives.

    Jim

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