NEW YORK, NY— On TikTok, sweaty New Yorkers have opened their cameras to give Mayor Zohran Mamdani a suggestion: air conditioning in subway stations.
The City's answer is not quite an air conditioner.
Mamdani, Gov. Kathy Hochul and the MTA announced a plan on Monday to study a thermal energy network beneath Lower Manhattan that could cool some of the City's hottest subway platforms and send the heat to nearby municipal buildings.
"There are few feelings worse than escaping the extreme summer heat only to find yourself on a subway platform that is even hotter," Mamdani said. "We can make our subway platforms cooler and more comfortable while putting wasted heat to work during the winter."
The proposed system would use heat already trapped underground as an energy source rather than simply trying to get rid of it.
The study will focus on the Brooklyn Bridge-City Hall 4/5/6 station and the Chambers Street J/Z station complex, where the MTA plans a major renovation.
Brooklyn Bridge-City Hall is among the hottest stations in the subway system, with average summer temperatures reaching 96 degrees Fahrenheit in 2025, according to the City.
Brooklyn Bridge-City Hall also serves as the terminal for the 6 train, where heat from trains dwelling at the station contributes to the station's high temperatures, according to the MTA.
If the technology proves feasible, the project could become the first thermal energy network installed in a U.S. transit system.
The problem is not that the MTA has never cooled a subway platform.
It has, but only where the infrastructure makes it possible.
In a rare example, Grand Central Terminal has a large chiller plant that produces chilled water, which the MTA can circulate through cooling units on the 4, 5 and 6 platforms below.
Newer subway stations have taken a different approach.
Stations on the 7 line's extension to Hudson Yards and the Second Avenue subway, for example, use cooling towers and what the MTA calls "air-tempered climate control."
Rather than fully air-conditioning the stations, the system can keep them roughly seven to 10 degrees cooler than the surrounding temperature while reducing humidity.
But replicating those cooling systems across other stations would require major new infrastructure.
For one, subway stations are not sealed spaces.
Stairways, entrances and sidewalk grates leave much of the system open to the outside air.
"Bringing down the temperature is a real challenge in a century-old system with open entrances and vents everywhere," Lieber said.
And, the systems come with a hot price tag.
Grand Central's 43 chillers cost about $10 million when they were installed in 2000.
Using the inflation-adjusted estimate cited by The New York Times, that would be roughly $17 million today.
Extending a similar approach across the city's 281 underground stations would put the rough cost in the billions.
The new thermal-energy-network proposal at Brooklyn Bridge-City Hall and Chambers Street takes a different approach, using the station's existing infrastructure to explore how excess heat could be put to work elsewhere in the City.
That could make the Lower Manhattan project less about turning the subway into one giant air-conditioned building and more about finding a way to manage the heat the system already produces.
The proposed system would use radiant cooling to pull heat from subway platforms.
Instead of relying solely on conventional air conditioning, radiant cooling uses chilled water circulating through panels or tubing. The cooler surfaces absorb heat directly.
The City reports radiant cooling can be 25 to 35 percent more energy efficient than traditional air conditioning.
At Brooklyn Bridge-City Hall, the system could absorb heat from the platforms and move it through pipes to geothermal boreholes beneath Chambers Street.
The Chambers Street station offers an unusual advantage: an abandoned center platform that could allow the MTA to test the technology without disrupting passenger areas.
The network could reduce reliance on fossil fuels by allowing excess subway heat to become a usable energy source, Mamdani said.
He said the study will also examine how much the system could reduce the City's energy costs.
The excess heat could be stored underground in geothermal boreholes during warmer months.
During the winter, that stored energy could be redirected to heat nearby municipal buildings.
The feasibility study will determine how much cooling the system could provide and how much energy and money it could potentially save.
The City and MTA will also examine whether geothermal infrastructure can absorb, store and transport heat between the subway stations and nearby municipal buildings.
That means the current announcement is a study, not a promise that riders will soon find air-conditioned platforms.
The MTA recently announced plans to rebuild the Chambers Street J/Z station, one of the oldest stations in the system.
The project will rebuild structures, replace tiles, upgrade stairways and restore the station.
The renovation is being funded through congestion pricing.
That construction gives the City and MTA an opportunity to investigate geothermal infrastructure while the station is already undergoing major work.
The City and MTA plan to award the feasibility-study contract this fall. If geothermal technology proves feasible, design work could begin in early 2027.
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