Why is one door always locked?

Factual Questions
1

I’ve noticed that many, many business offices have two glass doors right next to each other that, if they were both open, would make one big entrance. And yet, in many cases one of the doors is locked shut and has a sign on it that says “please use other door.” Usually I don’t notice the sign until I’ve unsuccessfully tried to open the locked door.

My question: why have two doors in the first place? Is there some cosmic force that commands “thou shalt have two doors to celebrate the grace of man, but thou shalt only open one of them as penance for man’s fall from grace,” thereby leading thousands of people to needlessly waist time pushing or pulling on a locked door before reading the sign?

2

For climate control, maybe? Opening both doors at once would let drafts in, heated or conditioned air out, and so forth.

3

This question seems to come up frequently. Here’s a link to the same question asked just yesterday, where someone posted a link to the same question posted two months ago:

http://boards.straightdope.com/sdmb/showthread.php?threadid=45158

You know the boards are getting busy when the same question comes up within 24 hours …

Arjuna34

4

BTW, welcome to the SDMB :slight_smile:

I found the old thread by searching for “locked” in the General Questions forum. The search engine is quirky (although it seems to be working better lately), but worth using. I usually search for a question first, then end up finding the answer to a more interesting question than the one I was going to post!

Arjuna34

5

My WAG is that if they’re both unlocked, the one door will rattle and bang around when the other door swings shut. In other words I have no clue.

6

My bad.
I gather that in the old thread the “save on heat and air conditioning response” was the most popular. I really think these savings would be minimal. The doors are still closed most of the time. The double doors to apartments are usually on;ly one of the first set of doors, the inner door is still closed. The “heat” lost should be proportional to the length of time the door is open as well as the area of the door and the difference in temperature between the foyer and outside. If maneuvering heavy things or fuddling with a door, the single door is open longer. Not that landlords are not saying this is why they do it, just that I have trouble believing it is worth their while.