Dear Umbra,

So the weather is turning hot again. I got my electric fans out of the closet. On the back of these, there are no indications of what amount of electricity they use. Could you illuminate which ones are most efficient?

Howard Nelson
Portland, Ore.

Dearest Howard,

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Not really. Efficiency is very important for commercial ventilation, and even home ceiling fans and oven fans are given an Energy Star label, but I fear our lowly personal fans don’t get similar levels of evaluation.

Better oscillate than never.

Photo: iStockphoto.

It does seem generally accepted that oscillating fans are more efficient than box fans, but I don’t entirely know why. One factor, of course, is power usage: according to a publication from New York State Electric and Gas, at 120 hours of run time per month, a 20-inch box fan uses 12 kilowatt-hours, while a 12-inch oscillating fan uses a mere 4 kWh.

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As for your specific fans, I suggest that you try to determine the amount of electricity each one uses, and then decide yourself how efficient they are using the convoluted technique I’ll describe in a moment. Fun!

Here’s how to research the watts used by each fan (or any other mystery object). First, of course, double-check all the appliance housing for a printed indication. In a regular home outlet, watts are amps multiplied by 120 volts, so even an amp listing would be helpful.

If you still have no luck, you have three choices for measuring watts and watt-hours. One is to buy a nice, simple watt-hour meter, which you connect to the fan, plug in, and read. Another is to buy a less-simple whole-house watt-hour meter, which an electrician needs to install. The third involves unplugging your appliances, racing outside and reading your electric meter, hollering at your assistant to plug in and turn on each fan one at a time, clocking the meter, and doing some serious math. Take a look at this random helpful website for more details on that type of scheme.

Now, my wacky instructions for evaluating efficiency: once you know the power usage of your fans, you’ll need to subjectively assess their airflow properties, since official cubic-feet per minute is a mystery. It may be helpful to have a panel of judges for this segment. Set up all the fans next to one another facing a chair. Taking turns, each adjudicator sits in the chair while another participant turns each fan on, then off. Judges should note the performance of the fans at each speed. You may wish to wear floppy hats or hold pinwheels to get a visual of the air movement, since human bodies (and overheated brains) vary quite a bit. Compare your answers and assign each fan a rating; then compare your performance rating with each fan’s watt usage. The one that cools best using the least power wins!

Maybe you’ll dump your box fans after the experiment, or maybe you’ll see that the fans are pretty much equal, and stop worrying about it. Before you do anything, please go read my ancienne columni, including information on fan placement and other options for keeping cool.