Nestled into a hillside not far from the Schenley Bridge, the Bellefield Boiler Plant provides steam heat to most of Oakland’s major institutions.

Built in 1907 to heat the library and museum Andrew Carnegie had recently donated to the city, the plant now services the Carnegie Museums of Pittsburgh, Carnegie Library's main branch, Carnegie Mellon University, Phipps Conservatory and Botanical Gardens, the University of Pittsburgh, Pittsburgh Public Schools’ administrative building and UPMC’s Childrens and Presbyterian hospitals.

A literal powerhouse, the plant goes largely unnoticed, said Kevin Hiles, chief financial officer of Carnegie Museums and chair of the consortium that owns and operates the plant.

“It’s one of those things like accounting," he said. "It just happens behind the scenes and people are glad it does, but they don’t really think about how it happens.”

However, there is one well-beloved clue to the plant’s existence, said the plant’s superintendent Bob Miller.

“When it’s very cold out, you see this white cloud," he said, "and that’s the hot gases mixing with the cold air — the 'Cloud Factory,' as we’re known.”

Writer Michael Chabon popularized the steam plant's whimsical "Cloud Factory" moniker in his novel "The Mysteries of Pittsburgh."

The plant can produce up to 480,000 pounds of steam per hour. In the plant’s operating room, engineers from Local 95 can monitor the entire system. Miller talked about meeting demand — putting on another boiler, taking one off — the way some people talk about putting on the teakettle.

“We know around eight o’clock everyone comes into the office, they turn up the thermostat, so we’re ready for it ... they’ll have another boiler on so we have the steam demand ready for them,” he said.

Before the plant switched entirely to natural gas in 2009, Bellefield ran on coal. Lots of coal.

“We would get 70,000-ton cars and each bunker would hold about five or six cars," Miller said. "We had to unload coal. We had to clean the boilers more often. We had to get rid of ash. That was a lot more work. That activity is gone. I’m an old-fashioned guy, I love burning coal. There’s an art to it.”

It’s an art Miller was introduced to by his father.

“My dad was a boilermaker," he said. "I wanted to be a boilermaker and my dad said, ‘No, you’re going to college.’ So I went to college. I worked at a bank and I said, ‘I didn’t like that,’ and then got down here. Simple. It’s in my blood.”

While Miller misses the bustle of coal, he’s not naive.

“With gas it’s a lot cleaner and easier," he said. "We did this voluntarily. I’m proud of what we have. I couldn’t do it without the guys I have here. It’s not me. It’s my guys.”

Standing on the spotless floor of the plant, half lit by sunlight streaming through windows that reach almost to the ceiling, Miller said he would prefer never to retire.

“It’s just ... knowing that I am taking care of hospitals, schools and it’s benefiting somebody," he said. "I don’t know, it’s just in my blood. I just love doing this. I don’t know how else to explain it, I just love doing it.”

If it weren’t for the telltale cloud rising from the plant’s remaining stack, it could be just another ornate building in a neighborhood of ornate buildings. But it's not. So drop by the museum, it’ll be warm there. The team just put another boiler on.

90.5 WESA Celebrates Inventing Pittsburgh is supported by UPMC.​