Ping, ping, ping, hissssss. 

If you live in a vintage building in Chicago, those sounds are the harbingers of autumn, as the radiators return to life on the first chilly night of the season. As a cold-weather city constructed mostly in the first half of the 20th Century, Chicago is one of the nation’s steam heat capitals, perhaps second only to New York (as we’re second to New York in everything). If your first apartment wasn’t heated with a radiator, you missed out on an essential Chicago experience, as well as some cozy winter nights.

Dave Bunnell, who graduated from the Illinois Institute of Technology with a degree in architecture, is the owner of The Steam Whisperer, a company specializing in the maintenance of boilers and radiators. As such, he’s probably the city’s number one expert on steam heat. We talked to him about the history of steam in Chicago, and why heat from a radiator feels so much toastier than forced air through the floorboards.

How widespread is steam radiator heat in Chicago? What proportion of dwellings would you say are heated this way in the city?

My guesstimate is probably in the range of 30 to 40% of the housing units are heated with steam. Some people may say, well, that’s just ridiculous. There’s no way there’s that many buildings out there. The thing is that steam heat is in large buildings. So you’ll have one building with 30 or 40 or 100 units.

Is there a particular era when installing steam and radiators was most common?

Pretty much everything before World War II, and actually some after World War II. From 1905 through about 1940 was probably the peak of the years we were seeing some of the best systems ever available. And that was a huge growth period for Chicago. So that corresponds with when the majority of the city proper itself was built, right during the steam era.

So as far as cities around the country, is Chicago pretty high in proportion of steam heated units?

Yes, I would say so. New York is probably the highest because New York was at least into the 1980s still putting in steam-heating systems.

A person sleeps on the bench next to a radiator in the North Western Station in 1970. Michael Budrys/Chicago Tribune

I’ve heard a story, and I don’t know if it’s an urban legend, that steam heat became popular after the 1918 flu pandemic because it was going to force overheating of units and make people open their windows and let the bad air out.

I’ve never heard it put that way, but the flu pandemic had a huge impact on heating systems, because they actually changed the code requirements for heating systems when the pandemic was around, because they didn’t know what was causing this. They thought there was something in the air that was causing this. And so what they did is they started requiring buildings to be ventilated. Essentially, they changed the requirements for heating buildings so you had to maintain 70 degrees in the building with all the windows open in the sleeping rooms. So people see these great big huge radiators and think that that’s what they have to have in the house. Usually, the reason those radiators are so big is because they had to heat the house with windows open.

So why did steam fall out of fashion after World War II?

It’s a mixture of different things. Forced air came in big time, at least in the United States, and basically, forced air can be installed cheap and fast. They were building so fast because all the GIs were coming home, and they wanted to start families and they had all these houses to build. And so they could install forced air systems cheap and fast, where putting in the piping for a hot water system or a steam system was a more labor-intensive and expensive way of doing things.

What are some of the biggest apartment complexes in Chicago heated by steam?

Probably the biggest ones are the ones along North Lake Shore Drive, the big ones right along the lakefront that are 12-13 stories. And the reason for that is the steam heating system — there are no issues with pressure at the bottom of the building. If you take water, for instance, the higher you stack it, it’s like a water tower, the pressure builds on the boiler. So you have a limit of how far you can go, how tall you can go on the hot water heating system. A steam heating system, you can go as tall as you want. The Empire State Building in New York City is heated with steam.

Why did they keep using steam in New York, but stop in Chicago?

Well, that probably has a lot to do with my old alma mater, IIT. There has been for a long time this attitude that steam is old and inefficient, you should be using hot water. The architecture program at IIT had a major worldwide influence on architecture; it certainly had a big influence on what was built in Chicago. So, you look at most of the really big buildings built in Chicago, through the ’50s, ’60s, ’70s, probably into the early ’80s were designed by architects who were related to IIT. It may go back to Mies van der Rohe, because he was a big name at IIT. Crown Hall, which is a major architecturally significant building worldwide, is heated with hot water running through the floor.

I lived in a steam heated building apartment for 10 years. Why does steam heat feel cozier than forced air?

When you look at heat, there’s three main ways to transfer heat. One is just like sunshine, it’s radiant heat. You have all this heat energy passing through the empty space between the sun and us. So you feel this radiant heat. Your skin gets warmer, because of that radiant heat. So that is actually probably the biggest way heat transfers. Another way is convection, so basically, if you touch your desk, heat from your hand goes into the desk, and your hand feels colder. The last way is through heating air. 

In terms of efficiency, that’s probably the order in which they are (efficient). Radiant heat is very efficient at transferring lots of heat. Convection also is. Air movement is very inefficient, because air has almost no mass, so there’s very little mass to heat in order to transfer heat. So now, let’s say you’re sitting in your apartment, you’ve got those nice warm radiators. The reason they’re called radiators is because they radiate heat. So what happens is radiant heat moves like a form of light. So anything that radiators can see, anything that light would be falling upon, actually gets radiant heat in the surfaces, which the radiant heat warms up. 

What radiant heat tends to do is it tends to increase the temperatures of all the surfaces in the room above the air temperature. Therefore, you’re much more comfortable, because everything you touch is warmer.

Now, I was talking to you about how the sound of fall is hearing that ping, ping, ping, hiss. And you said I shouldn’t be hearing that.

Yeah, if a system is working well. Now, some of the pinging, sometimes that’s just expansion noises, because sometimes when you heat up pipes from 70 degrees to 250 degrees, there’s going to be some movement. So sometimes the pipes are a little tight against the floorboards, or against a joist, so you’ll hear sort of a little bit of a thumping noise. Oftentimes, that may be more pronounced in the fall, because that’s when the system is going from dead cold to hot. Systems have been coming on in a lot of buildings, particularly this week, and we had a couple cold snaps a few weeks ago, they would have come on. You get a little bit of noise initially, but then oftentimes, it’ll settle down, because it’ll settle back to its winter position.