Why Steam Rises From San Francisco Streets

Photo by Grant MacHamer

If you’ve ever strolled downtown SF, especially along Market Street, you might have noticed plumes of steam rising from various vents and manholes. It turns out that this mysterious steam comes from a network of pipes that has been heating downtown SF for nearly a century.

Over 180 customers, including SF City Hall, the Moscone Convention Center, and the Golden Gate Theater, utilize steam for space heating, domestic hot water, air conditioning, and other uses.

Two massive boilers, located in SoMA and Lower Nob Hill, send the steam through over 13 miles of underground pipes that form the downtown steam loop. This system is responsible for heating over 37 million square feet of commercial, residential, and government buildings.

The company that runs this steam network, Cordia, services a 2-square-mile area in SF central business district.

Courtesy of Cordia

Both of the steam-generating plants use boilers heated by natural gas. The system’s combined heat and power (CHP) equipment generates 500 kW of electricity, essentially making the plant energy self-sufficient, according to Cordia.

Critics of the system point out that the system produces heat, but also wastes nearly 250,000 gallons of water per day, according to a 2015 story by CBS Bay Area.

Cordia addressed this issue by partnering on a water reclamation project to pump 30 million gallons of groundwater per year from beneath Powell Street Station. The groundwater is purified and used in the boilers, which reduces the amount of City drinking water needed.

Not every drop of water in the steam loop is wasted. Some of Cordia’s 180 customers do use a portion of the wastewater from their steam pipes for landscaping and flushing toilets, which includes SF City Hall.

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