What’s the purpose of revolving doors?

Dear Cecil:

Why do so many public buildings want you to use the revolving doors rather than the regular doors?

Cecil replies:

As with many things, there are two reasons — the ostensible reason and the real reason. The ostensible reason is that the revolving doors create an air trap. Since the interior of the building is never directly exposed to the outdoors, there’s less chance of all that expensively heated or cooled air getting out and running up your utility bill. An alternative way of accomplishing the same thing is a vestibule, where you have to pass through two sets of doors to get inside. Another reason for revolving doors is to prevent wind from howling down (or up) the elevator shafts and stairwells and blasting out (or in) the doors due to indoor-outdoor pressure differentials.

So much for the rationalizations. The real reason you’re told to use the revolving doors is so the real estate operators of the world can test your willingness to play ball. Do you follow directions and use the revolving door, or are you one of those independent types who insist on doing their own thing and entering through the swinging version? If the latter, be forewarned: when Donald Trump takes over, you’re history.

Send questions to Cecil via cecil@straightdope.com.

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