When you walk up to a building that has both a revolving door and a traditional swing door, which do you choose? Chances are, you’re in the majority and choose the traditional swing door. But did you know that by walking through a traditional door, you're letting heat or air conditioning escape, which in turn can drive up a building's energy bills?

"When you open a door, a lot of air goes in and out, and a revolving door helps with keeping that more stable,” Rini Paiva, vice president for selection and recognition at the National Inventors Hall of Fame, told The New York Times. "It’s a very convenient way to move people in and out of the building without having to keep a door open continuously."

A MIT research study showed that more than 75 percent of the patrons entering a building on campus avoided the revolving door.

I’m sure you’ve heard this before, but an MIT research team put this to the test. Yes, using that revolving door lets less of the outside air in and thus, the building doesn’t have to work as hard to maintain its optimal climate control setting. If everyone used the revolving door at the building used in the study, then 1.5 percent would be saved in total energy to cool and heat the building.

For each individual time you choose a revolving door, you save the building about 36 watt hours of energy — about enough to light a 60-watt lightbulb for 30 minutes.

So, next time you approach a building with a revolving door and a traditional swing door, please use the revolving door. The building owners will be thankful.

Editor's note: This article has been updated since it was originally published in October 2009.

Why using a revolving door makes sense
For starters, it's more energy efficient than a standard door that swings.