Why Does Steam Sometimes Come Out of Manhole Covers in Detroit?

From providing hot water to steam for coney dogs, Detroit Thermal carries vapor to scores of buildings and businesses downtown.

While driving around downtown Detroit, have you ever noticed a plume of steam coming out of a manhole and wondered where it came from? If so, you’re not alone.  

It’s something WDET’s Laura Herberg has wondered for the past decade. This year, she finally looked into the origin of all that steam. 

Climbing Down a Manhole

Dorothy Hernandez/WDET
Dorothy Hernandez/WDET

On a recent Thursday afternoon, I’m looking into a manhole in front of the Gem Theater in downtown Detroit. There’s no steam coming out of it, but officials from the company Detroit Thermal say this is one of a handful of places where they can access their network of steam tunnels.  

The company invited me to go down with them to take a look. But there’s no elevator or stairs here. To get to the bottom, I’ll have to climb down a 60-foot ladder. Luckily, the company has brought out a cable system that I can hook on to.  

Doug Jablonski, distribution manager with Detroit Thermal, explains this retrieval device will keep me safe in case I fall. 

“It’ll grab you and then we’ll lock you tight,” he says.  

Before I go down, Jablonski says, “Take your time. There’s no hurry. Some people may get claustrophobic. So if you feel awkward, odd, scared, there’s nothing wrong with saying I don’t want to do this. We’ll get you out.” 

A couple of crew members sink into the opening. And then — it’s my turn.  

Even though I’m hooked into the safety cable, I cautiously tiptoe around the hole. As I peer down, I can’t see the bottom, just the ladder and the first grated landing I’ll be climbing to. I slowly lower myself down and as I do, I’m hit with a blast of wind. Fans are used for airflow and cooling in the tunnel system. As I descend, the wind lets up.   

I lower myself rung by rung. I stare at calcium formations in front of me that give the man-made hole a natural cave-like feel. After a few minutes I finally make it to the bottom.  

Detroit Thermal
Detroit Thermal

Inside the Steam Tunnel

Standing 60 feet below the manhole cover and looking up, it feels like we’re at the bottom of an oversized well. In front of us is a brick-lined tunnel, about 10 feet wide and 10 feet tall at its peak. Grzech says it’s bigger down here than one might expect.  

“My understanding is they had miners coming in from all over back in the early 1900s to dig these tunnels out,” he explains. 

There are miles of this underground tunnel network, which was built to carry steam to various buildings in the downtown area. Detroit Thermal generates the steam using natural gas. In this tunnel, the steam is transported through a metal pipe, about a foot in diameter. Elsewhere in the network, there aren’t tunnels, but steam pipes are buried underground, carrying vapor to Detroit Thermal’s customers.  

Grzech says most of the companies they service use the steam for heating and hot water. A hospital uses steam to sterilize equipment. The steam is also used for things like brewing beer at the Detroit Beer Company and steaming hot dogs at Lafayette Coney Island. 

The buildings could make their own heat or use their own boiler, but Grzech says it’s more efficient and easier for them to have Detroit Thermal’s steam piped in. 

“From a safety perspective, they don’t have to worry about maintaining a boiler in their building, they just have a steam line,” he says. 

Dorothy Hernandez/WDET
Dorothy Hernandez/WDET

Why We Sometimes See Steam Plumes

As Grzech and I walk down the tunnel it’s dark.  There’s no lighting down here, so flashlights are used to illuminate the way. He shines his on an opening up ahead, pointing out where the pipe bends. It’s a turning point that branches off to feed the Fox Theatre and the Montcalm Fire Department. 

On the other side of the pipe, the tunnel opens up like it did at our entry point. About 4 stories above us, there’s another manhole cover. This one is in the middle of the street and every now and again a car tire runs over it. Grzech and I crane our necks up to look at the manhole cover.. 

Something’s missing. There’s no steam!

Dorothy Hernandez/WDET
Dorothy Hernandez/WDET

Grzech says that’s because it’s not common to see steam coming out of manholes in this part of their distribution network.   

“Usually when people see steam discharges from manholes that’s typically the part of our system where we have a buried pipe,” he explains.   

Grzech says sometimes you’ll see steam when it’s raining or snow is melting. Or sometimes there will be steam because it’s an indication that there’s a leak they need to fix. But Grzech says even if there’s no water on the ground and all the leaks are taken care of there will still be some steam plumes.  

“As long as you’re moving steam throughout the city you’re always gonna have some discharge of steam,” he says. 

So the next time you see a white plume rising out of a manhole, I hope you’ll picture Detroit Thermal’s network of tunnels and buried pipes carrying water vapor around underground Detroit — heating buildings, cooking hot dogs and at times, simply letting off a little steam.  

Listen: WDET’s Laura Herberg finds out the source of all that steam coming from manholes in downtown Detroit.

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  • Laura Herberg
    Laura Herberg is a Reporter for 101.9 WDET, telling the stories about people inhabiting the Detroit region and the issues that affect us here.