Ask Mr. Green: Simmer or Nuke?
I have about a quart of soup left over. Is it more efficient to reheat it on my gas range or in my microwave?
--Paul in Kalamazoo, Michigan
A microwave is a lot more efficient for reheating than a stovetop, since it takes 80% less energy to warm up relatively small amounts, according to the EPA. Although the microwave needs a lot of electricity, it's a relatively short burst of power. As the immortal Yogi Berra might have put it, "A watched pot never boils, but it boils quicker in a microwave."
While stovetops are less efficient, you can make regular gas or electric cooking more efficient by matching the size of the burner to the size of the pot—a 6-inch pot on an 8-inch burner can waste a goodly portion of a burner's heat—and by keeping a lid on unless the recipe forbids.
Though cooking accounts for only 3% of total U.S. greenhouse-gas emissions from residences, every bit we can cut is significant because we use so much more than we really need. Per capita, we now consume six times as much electricity and twice as much natural gas as we did in 1950. Whether our overall standard of living has improved correspondingly is open to debate.
Saving energy isn't just green but also massively cheaper than wasting power the way most households do. At your present utility rates, to heat that soup on the stove would cost you about three times as much as warming it in the microwave. As I always say, even if global warming didn't exist, there would be plenty of other reasons to save energy.
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