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| By Tik Root |
| There are seemingly endless reasons to boil water. But how to most efficiently achieve the task has long been up for debate. |
| Tom Murphy, a physicist at the University of California San Diego put the various theories to the test in 2012. "I thought the microwave would be quite good," he said in a recent interview. He thought the same of electric kettles, but was more skeptical of the stovetop option, though he decided to test that, too. |
| Dr. Murphy focused on boiling water, but stovetops and appliances are used for heating up all sorts of things — and they can use significant household energy — so his experiment helps underscore how small changes might boost efficiency. |
| Taking readings from his electric meter, and rigging a laser to monitor his gas usage, he calculated how much of the energy actually went to heating the water, versus dissipating along the way. "You have all these loss channels," he said. Minimizing that loss means using fewer resources and likely emitting fewer climate-changing emissions. |
| As Dr. Murphy expected, the gas stovetop was not very efficient. With the largest burner on full-blast and no lid on the pot, he found that only about 15 percent of the natural gas being burned was converted to heat in the water. If you add a lid and use a small burner (which takes longer), you can potentially double that number but, he said, "the gas stove tops out at about 30 percent." |
| While Dr. Murphy did not test an electric stovetop, other estimates tend to rate their efficiency considerably higher than gas ones. But Dr. Murphy said that electric stoves are also conditional on a host of factors — from burner geometry to the cleanliness of any reflective plates. |
| The microwave was a bit better; it clocked in at about 43 percent efficiency. But the figure was still about half of what Dr. Murphy had hypothesized. The kettle came the closest to matching its pre-experiment hype. |
| Most kettles, Dr. Murphy said, locate the heating coil directly in the water and have at least somewhat insulated sides, which both reduce energy loss. This enabled his setup to hit 70 percent efficiency. But those findings come with a few major caveats. |
| Foremost is that efficiency largely depends on your energy source. By the time electricity from fossil-fuel-powered plants has reached your home, Dr. Murphy notes, it's already lost about 60 percent of its energy (some estimates have that number higher). That scenario, he said, could drastically hinder the performance electric stovetops and microwaves. |
| Kettles suffer from the same electricity issue — but also come with additional drawbacks that Dr. Murphy says can cause their efficiency to vary widely. The auto-stop function, for instance, often runs much longer than is necessary, which wastes energy. And people tend to overfill kettles. "Habitually, you're just heating a lot more water than you need to be," he said. "In practice, you're not likely getting any better than a microwave." |
| To get the most out of your kettle, Dr. Murphy says you should only boil as much water as you need and monitor the boiling point, so you can manually shut it off. |
| Dr. Murphy also looked into starting with hot water from your tap as a way to improve results (the myth that cold water boils faster has been thoroughly debunked). He found that it can probably help, because hot water systems are relatively efficient. But because a certain amount of the hot water will inevitably get left behind in your pipes, unused, the benefits of starting hot are greater when you're boiling large pots of water for, say, corn on the cob. |
| Dr. Murphy didn't test methods such as induction cooktops, which others have since found to be quite efficient. Technology is always changing (scientists in Oregon, for example, have developed new surfaces that could improve boiling efficiency) but he doesn't see any breakthroughs on the horizon that will make boiling water miraculously less energy intensive. The biggest thing individuals can do, he said, is be vigilant about our own habits. |
| "You just have to care about it," he said. "You have to pay attention." |
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