Big Fan

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Here’s some math on the costs of staying cool this summer: A decent window A/C unit costs roughly 14¢ an hour on your utility bill. A larger central-air system will cost you about 36¢ an hour to run. The energy needed to keep a typical ceiling fan humming, meanwhile, adds up to 1¢ for every three hours it’s on.

Figures come courtesy of the New York Times in a humongous story about the pros, cons, brilliance, and limitations of fans. While fans are obviously far less expensive to buy and operate, any argument for using them exclusively, with no A/C whatsoever, literally goes out the window on those nights when it’s 90 degrees and humid and even a hurricane-strength wind wouldn’t cool your home off.

One especially interesting point in the story is that today’s homes are tougher than ever to cool off, and why that is has nothing to do with global warming. Instead, architects who designed condos, offices, and houses in the last half-century tended to view ventilation and air flow as afterthoughts. The owners and workers in these buildings love views, so the architects provided lots of windows—and those windows created a stuffy greenhouse effect inside, which no fan could counter. And who needed fans anyway, what with air-conditioning?

Perhaps if your home was built in the pre-A/C days (and it hasn’t been dramatically altered since), it can still be cooled off efficiently with strategically positioned fans. The Times story explains:

DON’T ask most architects how to cool a house with fans. Nathan Kipnis, the principal of an energy-conscious architecture firm in Evanston, Ill., pinpoints the 1920s as “the state of the art for ventilation.” Houses and apartments had awnings and porches to keep out the baking sun; transoms and operable skylights promoted air flow.

But “air-conditioning allowed people to forget everything they knew about common-sense ventilation design,” Mr. Kipnis said.

The easiest thing to do is just keep the A/C pumping. That’s also the more costly and environmentally un-friendly thing to do. While more complicated, a hybrid approach, in which fans are used most days, and the A/C is switched on as a last resort on the sweatiest nights, is probably doable, though. The payoff is cheaper utility bills, less environmental impact, and more fresh air.