What’s on your ceiling can affect how you feel—and how much you pay for electricity every month. If you have a ceiling fan, you can harness the power of the wind chill effect to feel cool even when your thermostat is set higher than usual.

In other words, what’s bad news on a 20-degree day can be great news for your comfort at home. The perception that the temperature is lower because of air flow against your skin (that’s the basic idea behind wind chill) means you don’t have to tax your air conditioner to feel perfectly cool.

“Even if the air is warm, when you feel it moving past you, you feel cooler,” said Energy Efficiency Programs Manager Laura Matney. “Think back to the days before air conditioning: People had little fans to wave in front of themselves. It’s exactly the same principle.”

It’s the same principle—more effectively executed now that ceiling fans are widely available, inexpensive, and easy to install. If you have them, use them—in a counterclockwise direction so you’re sure to benefit from the breeze. (In winter, the theory goes, you can push the warm air down from the ceiling by changing your fan’s direction.)

But know this: A ceiling fan doesn’t cool the air; it cools people. So there’s no point in leaving one on when you aren’t in the room. Doing so defeats the purpose, in fact, because you’re using electricity to power the fan even when it isn’t doing its job.

It will do that job quite well, however, and so installing one in a room that gets frequent use is well worth the expense. Be sure to match the size of the fan to the room. Most products include that information on the box, but here’s a rough guideline:

• Fans up to 48 inches are right for a 100-square-foot room
• You need a 50-54-inch fan for rooms over 100 sf up to 400 sf.
• Rooms larger than 400 sf require a fan of 56 inches or more.

You can install a fan on a screened porch or other outdoor area, but make sure that you use a fan rated for the water exposure it’s likely to get. An indoor fan simply isn’t right for outdoors—even in an area where it’s unlikely to be rained on directly. The humidity can wreak havoc on a motor that isn’t rated for moisture.

You won’t necessarily need or want a light fixture in your ceiling fan, but we’d be silly not to point out that we recommend LED bulbs for any you do have. And as if energy savings aren’t tempting enough, we’ll add a sweet little rebate on ENERGY STAR® LED bulbs to help with the cost.