Sometimes it escapes:
Mark Vanhoenacker explains the steam system under NYC:
Con Edison, New York City’s venerable power company, pipes steam to customers in Manhattan just like any other utility product (such as gas, water, or electricity). The steam—some purposely created, some a ‘waste’ byproduct of electricity generation—comes from power plants. Commercial, urban steam systems of this size are rare, and New York’s is the world’s largest.
(Lockport, N.Y., had the world’s first urban steam system, in 1877, and Denver’s is the world’s oldest in continuous operation.) NYC’s system has 105 miles of main pipes, 3,000 manholes, and reaches around 1,800 buildings—everything from the Empire State Building to United Nations Headquarters. Steam connections run from the southern tip of Manhattan to 96th Street on the West Side and 89th Street on the East Side.
What’s the steam used for? A little bit of it is used as, well, steam—to operate laundries and even to sterilize hospital equipment. But a lot of it is used to heat buildings and their water supplies.
The Dish 