Revolving Doors

RM: This is 99% Invisible. I’m Roman Mars.

RM: The story goes like this, and keep in mind with all these origin stories when they sound a little too much like stories, they’re probably not completely true. But anyway, the story goes like this: Theophilus Van Kannel hated chivalry. There was nothing he despised more than trying to walk in or out of a building and locking horns with some other man in a game of “After you. No, you first. Oh no. No, of course. You first. No, I insist, you first. Thank you.”

SG: And more than that socially mandated deference to other men, Theophilus Van Kannel hated opening doors for women. And so Theophilus Van Kannel, or Theo for short, took a German innovation from 1881 the Tür ohne Luftzug or, “Door without draft of air” he made some improvements to the design and in 1888, was awarded an American patent for the improved revolving door. The first one was installed in Times Square in 1899.

RM: That’s our producer Sam Greenspan.

SG: Van Kannel’s improved revolving door had three compartments and weather stripping to ensure an energy efficient fit inside the door frame. His 1888 patent states that “It is perfectly noiseless in its operation and effectually prevents the entrance of wind, snow, rain, or dust. Either when disclosed or when persons are passing through it.”

RM: And as a bonus, annihilates any chance of social interaction that one might have while entering or exiting a building. The motto of Theo Van Kannel’s revolving door company was “Always open, always closed”. And so for the past 100 plus years, we have had the solution to keep dust and noise and rain and sleet and snow from entering our buildings. And yet, the likelihood that you’ll actually use it is very, very low.

Male Speaker: The problem is that people don’t use revolving doors because they’re heavy or they feel like they might get stuck in them. Compartments terrify people.

Roman Mars: And this shouldn’t be a big surprise. When you’re approaching a revolving door, it’s always hard to tell, how hard are you going to have to push it to get it going, and if it’s already moving, you have to time it just right. And there’s also the anxiety of getting a limb caught, or maybe your bag, and if oh man, you’re walking with someone and talking to them, it’s a little bit bigger of a revolving door and you actually get there with them, and you’re with them like really close even for that few seconds and it’s just…..whew, yeah, deep breaths, deep breaths. Whew.

SG: And if you’ve read Alan Moore’s Watchmen, you may remember that detail about how some of the superheroes are weary of capes because one time their caped crusader colleague Dollar Bill got his cape caught in a revolving door and was thus immobilized as a bank robber approached him and shot him in the head point blank. [gun shot]

RM: As long as you can tell if you need to push or pull to open the door, and that subject could be a whole episode end of itself, swinging doors are just easy. And most of us, unlike Van Kannel, are well adjusted human beings who actually do try to open the door for each other.

AS: Anytime you have a stream of people walking together and the first person in that line opens the swinging door, the rest tend to follow.

SG: So this is Andrew Shea.

Andrew Shea: My name is Andrew Shea. I’m a graphic designer, writer and educator in New York City.

SG:: Andrew’s obsession with revolving doors started when he was in graduate school.

Andrew: I was doing my thesis on designing for social change and a good friend of mine was visiting. He found out what I was doing and he pointed to the revolving doors and he’s like, “If you want to design for social change, I wish you would get people to use revolving doors more often.” That was his challenge to me.

SG: Andrew dove into the literature on revolving doors which was shockingly quite slim. But he did come across a study.

Andrew: A study done by some MIT students. I think they were in the urban planning department. But it was focused on sustainability and it was the only resource I could find out there that seem to have authoritative information about revolving doors and their impact. And it had a lot of math in it, I kind of avoided the math because I didn’t know how to interpret it.

RM: But you don’t really need to see the math to understand the logic. The basic idea of how a revolving door saves energy is that revolving doors never open.

Dan Wesolowski: They can prevent the free exchange of air from the outside to the inside. As the people move through the revolving door, they don’t open it. The only air that leaks through is either the actual air that’s being transported with the people in the chambers of the revolving door, or whatever leaks around the weather stripping.

RM: That’s Dan Wesolowski.

DW: Howdy.

SG: Dan was one of the authors on the revolving door study.

RM: Back when he was a grad student at MIT, he works on a project studying people’s behavior with respect to revolving doors and the energy savings associated with using revolving doors in large buildings.

SG: And in some ways, it’s a study that will not leave him alone. We were not the first people to contact him for an interview about this.

Dan: I don’t understand it. You know, I’ve got like 20 peer-reviewed publications on material science and engineering and what do I have like constant contact about? A term paper I did 8 years ago.

RM: Anyway, Dan did a bunch of science that sounds like this.

DW: Latent heat associated with all the water vapor that is in that material.

RM: We didn’t really give you enough context to understand that a little bit, but here’s the result.

DW: There’s 8 times more air exchanged when you use the swing door than when you use the revolving door.

SG: Or put another way.

AS: Revolving doors exchange 8 times less air than swinging doors.

SG:: That’s Andrew Shea again, the designer in New York. And this factoid really resonated with him.

AS: Which makes total sense, because opening a swinging door is like tearing a hole in a building. All that heat or air conditioning leaks out and the building has to kick in the high gear to make up for that temperature and humidity fluctuation. Dan Wesolowski and his team observed a building on the MIT campus that had both revolving doors and swinging doors and found that the revolving door usage sat at about 25%.

SG: The team realized that in addition to conserving energy and helping the environment, they could also save MIT more than $7500 annually if everyone just used the revolving door in this one building. And they found they could raise revolving door usage at that building to 60 or 70% with just some simple signage. And even though the MIT study was done in Boston and Andrew was in New York,

RM: It seemed like a pretty transposable data set. So all these inspired Andrew Shea in New York City. He decided to take up his friend’s challenge back from when he was in grad school and see what some simple observation and signage could do for one building in New York.

Andrew: My building was at Columbia University. It was the Applied Sciences building, it’s a brand new building. There’s three sets of swinging doors and three sets of revolving doors at the one entry point of this building.

SG: Andrew started by just by watching the building.

Andrew: I spent probably all together about 2 months, once a week, I think it was Tuesday mornings. Some of those weeks I was there for twice a week, Tuesdays and Thursdays. I watched people exiting and entering the building and counted the number of people.

RM: And he counted for about 20 hours in that 2 month period.

Andrew: I discovered that only 28% of people were using the revolving doors. So, my first intervention was just to create a very basic sign. I took an 8 1/2 by 11 piece of paper. I wrote really simply, “Please use revolving doors.”

SG: He added that factoid about revolving doors exchanging 8 times less air than swinging doors.

AS: It was very crudely taped onto the swinging door. It caused 58% of people to then go ahead and use revolving doors.

RM: So that’s a 30 point increase.

AS: It was a 30% increase. Yup. And of course, I wanted to know how I could get that number even higher.

SG: Andrew made a second sign in the shape of an arrow.

RM: And this arrow was smaller than the first sign.

SG: But then revolving door usage actually fell 5 points from his previous attempt to 53%. So Andrew tweaked it, made it larger and he also made it match Columbia University’s visual identity.

AS: Columbia has like a light blue and a dark blue color palette in their branding system. So my hope was that the branding would help people connect with it more and take it more seriously. And IN fact that 71% people end up using the revolving doors as a result of that.

SG: 71%! That’s up 43 points from where he started at 28%.

RM: Here is 99PI HQ, we were curious to find out if that could happen here in the Bay Area.

SG: So I went with our intern, Avery Trufelman, to go stake out a building in downtown Oakland.

AT: 4, 5. 6. 7 with the swinging doors.

RM: This is Avery and Sam in the observation stage. The vestigial scientist part of me has to remind you here that all the data sets we’re talking about today are very small. So, understand that. But everyone’s observations are aligned, given the choice, revolving doors just aren’t that popular.

SG: So it’s been 2 minutes into our experiment so far, how we doing?

AT: We’ve got 12 for swinging. 0 for revolving. Suffice to say, nobody is using the revolving doors.

RM: And when someone did use a revolving door, it was notable.


SG: Okay. Mark it one. Revolving door.

AT: Wow, what a champ.

Roman: Aren’t they adorable?

[gasps] [laughs]

SG: That’s 2.

AT: 2 for revolving door.

RM: After a half hour, they tallied up the results.

SG: Right. Tallied up. How’d we do?

AT: 259 people used swinging doors. 4 people used revolving doors. In a 30 minute period.

SG: Okay. So, should we —

AT: So, yeah. Let’s tape up these signs.

RM: These are the signs designed by Andrew Shea. It’s an arrow that says, “Please use revolving door. They exchange 8 times less air.”

SG: Notice the people are using the revolving door as we’re walking.

AT: Exactly. Alright. All the signs are up.

SG: All right. Let’s see what happens.

AT: That man saw the sign and uses the revolving door.

SG: Followed by another guy.

AT: Followed by another guy using the revolving door.

SG: This lady’s even waiting for the revolving door to finish —

AT: Oh right.

SG: — so she can get in and go the other direction.

AT: They’re already increasing the revolving door traffic flow.

SG: It doubled in less than five minutes.

RM: And after another 30 minutes, team 99PI tallied the results.

AT: One for revolving.

SG: Four. Three. Two. One.


AT: Alright.

SG: Alright. How’d we do?

AT: Okay. So these are people who used the swinging doors even though the sign was on them. 5, 10, 15, 20, 25, 30, 35, 40, 45 — 145, 150, 157. And then people who used the revolving door this time are 5, 10, 15, 20 — 65, 69.

SG: So with no sign, this building between the hours of 12:30 and 1:00 on a Monday, originally it was 1.5%. After the sign —

AT: 30 and a half percent of people went through the revolving doors when there was a sign pointing to them, as opposed to 1.5% without the signs. So, not too shabby. Yeah.

RM: Now, we did not try testing all the variations, so people could’ve interpreted the signs as intended, taking in the message that revolving doors were more energy efficient and adjusted their behavior accordingly. Or they could’ve just thought the swinging door was out of order, or they could’ve just noticed something was out of the ordinary and it nudged them into using the revolving door. Whatever happened, this much is clear. Putting up an arrow on a door makes people do things. Now if you wanna get people to use a revolving door, that’s a good place to start. And with that, Sam and Avery left the lobby of that building and took down the signs. Just like Andrew Shea took down his signs at Columbian and shared his results with the powers that be, but nothing ever came of it. Dan Wesolowski says that MIT did eventually incorporate some of the basic concepts of his study when they created sustainability stickers to place on their outer doors, although he thought his signs were better. But another really powerful way to increase the use of revolving doors is with to address the issue in the architecture itself. It turns up there are actually much more effective revolving doors out there. Like at the Marriott hotel in Oakland. It’s much larger, it’s the visual focus of the entrance and it has three dividers which are actually big enough for you to be inside one of them with a stranger and not feel too weird about it. And they revolve automatically. And perhaps, most importantly, the doormen won’t open the swinging doors for you, unless they already see you’re going for them. So if you can’t get institutional buy in, or get a brand new gigantic revolving door, Andrew Shea has a revolving door action kit that you can download for free and take to your local office building. Scotch tape not included. It’s BYOST. FYI. YMMV. ICYMI. BRB. OMG.

[background music about revolving door]

Roman: 99% Invisible was produced this week by Sam Greenspan, Avery Trufelman and me, Roman Mars. We are a project of 91.7, local public radio KALW in San Francisco in the American Institute of Architects in San Francisco.

    1. We refer to those doors as Sally Ports – You cannot open the second door when the first door is open. It’s a common practice in building security.

  1. Yeah, similar to the link above, I’ve been wondering about the comparison to compartmentalized entries where you walk through two sets of doors. Almost think Best Buy entrance where you walk thru two pairs of automatic doors. In a small enough design, it would seem to be similar in size to a revolver.

  2. There should be a study about how much kids use revolving doors! Also, does anybody know if the doors’ energy saving potential is ruined by those automatic/powered revolving doors you often see in big hotels and office buildings?

    1. Cj

      Since I listened to this episode I’ve noticed nearly every revolving door around my work place in Sydney. They are all automatic too.
      As for using them, always. I still get a kick out of them.

  3. G

    If I see one, I usually use it. Not only because it obviously saves energy, but also because it’s mechanically interesting and retro-cool.

    Why some people may avoid them: fear of getting trapped if it jams, and the fact that the visual appearance of it somewhat confuses the sense of 3-D depth vision.

    When you walk through a door that’s mostly glass, such as at a grocery store or office, what you see is a clear view of the building interior, broken only by the horizontal line of the door opening rail. What you see when you approach a revolving door is a set of vertical lines with an unclear depth relationship between them, that pull and tug at your depth vision as you try to see past them into the building. This can create the impression that if you don’t pay close attention, you may walk right into the edge of one of the door panels and get hurt. That type of aversion is an avoidance reflex similar to what birds use when flying in the vicinity of moving objects such as large wind turbine blades that they can see moving.

    The way to solve this is to offset the entrance to the door, sufficiently to one side (the right in the USA, the left in the UK, per local “driving on the road” customs), so that what you see as you approach is the same as for a swinging door: a clear view into the building broken only by the horizontal push-rail on the door panel. The vertical axle would be to one side or the other, rather than dead-ahead, so it doesn’t confuse the view.

    Lastly, the door mechanism should have a detent and a flywheel drive mechanism such as to stop rotating when the visible door panel is 90-degrees to the axis of travel, so it always presents a uniform appearance and there is no risk of walking into the edge of a partially-rotated door panel.

  4. TED

    This episode seemed heavily focused on signs, with only a minor focus on revolving doors. Is a sign episode in the works?

    The power of signs reminded me of when I was in my undergraduate about 8 years ago and some of my classmates and I were discussing this topic. Someone came up with a simple test of the power of signs, uniforms, etc. We printed out a simple sheet of paper on the Engineering main computer labs printer that simply read “Do not remove this sheet of paper.” The sheet paper remained in place on that printer’s output tray for several months before vanishing.

  5. Thomas B

    I avoid them, I suppose I’m part of the problem. I don’t feel like any new designs actually take into account people who find the experience deeply unsettling.

    I’ve had the door bang into my heels. I’ve been trapped in compartments where I’m waiting on someone who moves incredibly slowly, or been shoved forward by someone moving incredibly fast. And while, yes, people can shove past on sidewalks, something about creating an artificial bottleneck, or maybe putting a heavy plate of shovable glass between you seems to empower the impatient.

    I’d much prefer we just starting using more vestibules coupled with air curtains, which would have the same benefits without creating an artificial traffic jam in an entryway.

  6. Here in Seattle, pretty much all the buildings with revolving doors include giant-ass signs telling people to use the revolving door, lest they waste energy and destroy the environment (or something to that effect). In the passive-aggressive NW, it seems to work.

  7. Bryan A

    The phrase “eight times less air than” doesn’t make sense mathematically, and it was used multiple times in this episode. It should be “one-eighth as much air as”….

  8. Alex C

    I listened to this on the way to a conference then used the revolving door to get in. The guy in front of me did not. It gave me a smile.

  9. headcase

    I’m one of those freako germaphobes who chooses ingress/egress based on whether or not i have to push or pull the door. If I have to pull a swinging door next to a revolving door into which I push, I choose the revolving.

  10. JFS_II

    You didn’t even mention Stack effect? It’s the real reason the revolving door was invented. Difference in air temperature between indoors and outdoors means that air inside a building will move and attempt to equalize the pressure – warm air moves upwards in winter (sucking in cold air at the bottom) and gets pulled down/in by the air conditioned space in the summer. In both cases, it’s a vast amount of air attempting to move through the path of least resistance – the doors to the building.

    The first skyscrapers were naturally ventilated, and during their construction the realization was made that the doors would be nearly impossible to open (you can still notice this nowadays in buildings with poor mechanical design). The revolving door creates a constant seal between the indoors and outdoors, which means the air pressure can be different and the door isn’t difficult to move. Airlocks are another way of doing this as people in northern climates can attest to (where doors can be hard to open if one side of the airlock/vestibule is open), but they aren’t as good as a revolving door because the possibility of breaking the seal is there. Modern HVAC design has taken care of a lot of issues arising from stack effect in large buildings, but air pressure making doors very difficult to open is still a real phenomenon :)

  11. Giorgio Venturi

    There is a simple explanation for the jump from 47% to 75% and it does not imply branding: it’s social conformity. Once a certain threshold is passed, people simply conform to the observed behaviour of the majority.
    Strange this factor was not mentioned in the MIT study

  12. Keith

    I work in Albany New York at a seemingly inefficient building, The “Empire State Plaza”, home of New York State government. There are revolving doors at several entrances. A perfect place to see how often the doors were used.

    My 7 year old daughter and I replicated Sam and Avery’s door use study. In 15 minutes of use at 12 noon the numbers totaled 37 swinging and 24 revolving. A total of 61 users.

    There were a few interesting observations, If someone was carrying or rolling luggage they were less likely to use the revolving door. Once,a mother was pushing a small sun stroller with her toddler, The mother tried to use the revolving door, but she could not fit in the doorway. Thankfully, they did not get stuck. I was relieved this occurred before any signs were put up. The unintended consequence of signage was not a factor. This is how this space worked, or didn’t quite work.

    A simple sign is more than just the words on a page. A sign could have implied meanings. Unwritten, and maybe more powerful than words. Could the sign imply, “out of order”, “broken” or “locked”. There are many possibilities. We opted to not put up any signs for this experiment.

    After watching the various uses of the doors, if a door was in motion, another user was more likely to use that door than if the door was not moving. This was nearly equal for swinging and revolving doors. We later noticed there was a sign that said on one swinging door, “Please conserve energy, use revolving door” It was unclear if this had any affect on any of the user’s decisions.

    After we finished our observations, we went down into the concourse. A huge hallway connecting various parts of the building. We were surprised to find that we had to walk through another bank of revolving and swinging doors. Here was an air lock from the first set of street side doors that we were observing. It brought me great relief to find out that there was a design in place to avoid all the warm air to go roaring out the exterior doors. We learned so much from your story and this experience.

    Thank you 99%!nvisible.

  13. Revolving doors can be somewhat of a nuisance, but they really are great to prevent that change in air flow. You still end up with the chivalrous issue at the entrance to the revolving door. “You first, Sir. No, I insist, you first Sir!”. A company in South Africa called Turnstar Systems manufactures a manual revolving door which is really easy to turn and in fact requires a speed controller to slow it down! Take a look at this website,

  14. Why do buildings always have both revolving and swinging whenever there are revolving doors? I believe because of the Cocoanut Grove fire in 1942 Boston in which people panic-stampeded and got caught in the revolving door resulting in many trapped victims.

  15. Claire Meyler

    I love revolving doors!

    I especially love the revolving doors at the Wichita Airport. They are HUGE. They are about double the width of other revolving doors, so there isn’t the same claustrophobic feel. Also, they start turning automatically as you step into them, so there is literally no effort needed, no wondering how hard to push, etc. The doors turn at a nice measured pace, so you and your luggage can easily go through. I think this is an example of well-designed revolving doors, and I’m a bit surprised that 99pi didn’t opt to explore alternate designs of revolving doors. This would have been a good example of doors that are designed to address some known problems.

  16. The “Revolving door action Kit” link is broken!
    I wanna post them on two Revolving doors in my home city,
    “please Help me Andrew Shea, your my only hope”
    [I thought a Star War reference might get more attention]

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