The Case for Turning Subway Waste Heat Into a Climate Resource

By Noor Malik

“Transportation and buildings are among the two largest sources of greenhouse gas emissions in New York City. If we’re going to be serious about fighting climate change, we need solutions that address more than one sector at a time.” — Julie Tighe, President, New York League of Conservation Voters Education Fund

If you’ve ever stood on a subway platform in July and wondered why it feels like the inside of a convection oven, you’re not alone. But what if that heat, the same heat that makes New Yorkers fan themselves on the B platform, could actually warm a building across the street?

That’s the premise behind thermal energy networks, or TENS. And on the morning of May 27th how New York could get there. The event was the latest in our ongoing Con Edison–sponsored dialogue series, bringing together policymakers, advocates, utilities, and practitioners to advance the city’s clean energy transition.

NYLCVEF President Julie Tighe opened the conversation by framing what’s at stake: buildings and transportation together account for the bulk of New York’s greenhouse gas footprint, and meaningful decarbonization requires thinking about those systems as interconnected rather than siloed. Thermal energy networks offer exactly that, a fundamentally fundamentally about those systems as connected rather than siloed. Thermal energy networks offer exactly that, a fundamentally different way of thinking about how we heat and cool our city. Rather than every building and every subway station handling its own energy in isolation, these systems allow neighborhoods and major facilities to share thermal energy through connected pipe networks.

Moderating the discussion was Sydney Mainster, NYLCV Board Member and Vice President of Sustainability and Design Management at the Durst Organization. Here’s what the panelists shared.

Greg Koumoullos, Department Manager, Thermal Energy Networks, Con Edison
The Rockefeller Center Pilot: Running Pipes Through the Subway

Greg Koumoullos has spent the last four years at Con Edison working almost exclusively on thermal energy networks, and he was quick to explain what the term actually means in practice. A utility thermal energy network is, at its core, a water-based, closed-loop pipe system that transfers heat between buildings, allowing them to electrify their heating and cooling while using far less energy than a conventional air-source heat pump would require.

And the thermal resources that feed these systems don’t have to come from deep underground. Buildings themselves generate enormous amounts of waste heat, office towers, data centers, and large commercial facilities are constantly cooling their interiors even in the middle of winter, sending that heat out through rooftop cooling towers and up into the atmosphere. Con Edison’s Rock Center UTEN project is designed to capture exactly that.

The project connects three buildings, 1221 Avenue of the Americas (where the event was held), 605 Fifth Avenue, and a building directly across 49th Street, to a network that will source waste heat from the Rockefeller Center campus. The numbers alone are striking: 3.5 million square feet of office space, 12,000 linear feet of piping, over 10,000 gallons of circulating water, and an energy center being built in a repurposed loading dock not far from where Saturday Night Live sets are assembled.

But the most remarkable engineering challenge turned out to be getting the pipes from one side of the street to the other. Rather than trenching through the street — which turned out to be hopelessly congested with existing utilities — Con Edison worked closely with the MTA to route the pipes through the roof of the 47th–50th Street Rockefeller Plaza subway station, running 10-inch pipes across the concourse level ceiling.

“I can’t tell you how many people said, ‘you’re going through the MTA station? No way.’ So, it’s getting that relationship right. And that’s what Con Ed can bring to these projects — not just the engineering, but the trust.”

Where things stand:

Con Edison filed the Rock Center pilot with the Public Service Commission in July of last year. As of this discussion, PSC approval was expected within weeks, after which the project would move into customer enrollment and construction, with full operation anticipated within 18 months to two years.

Ricky Li, Senior Manager, Climate Sustainability Planning, MTA Construction and Development From Climate Hazard to Decarbonizing Resource: The MTA’s Thermal Vision

Ricky Li leads climate sustainability planning at the MTA, and his team is working toward an ambitious goal: cutting MTA greenhouse gas emissions by 85% by 2040. But before getting to that, he wanted to address something most New Yorkers have wondered about, and few have explained to them: why is the subway so hot?

It turns out that the heat comes from several sources. Air conditioning units on subway cars discharge heat directly into the station. Braking energy, though about half of train cars now have regenerative braking, still produces significant heat through onboard resistors when the regenerated electricity can’t be fully absorbed by the system. And passengers themselves are heat sources in a system that was never designed with mechanical cooling in mind.

The subway’s primary cooling mechanism is what engineers call the piston effect; he displacement of air by incoming trains that creates a brief breeze on the platform. When the subway was built, that was enough. But with an average of 18 days a year above 90 degrees already, a figure projected to triple by mid-century; passive ventilation is no longer a sufficient answer.

Rather than framing extreme subway heat as simply a problem, Li’s team is asking a different question: what if it’s a resource?

The MTA is currently piloting a radiant cooling system at East Broadway station — the first of its kind in any mass transit system in the world. The system uses panels with low-temperature chilled water running through them to cool passengers without any forced air, similar in concept to how a radiator heats a room, but in reverse. One key advantage: no air filters, which means no buildup of the steel dust that makes conventional fan coil units so difficult to maintain in subway stations. “When the system is running, what it would feel like is similar to how you feel walking down the frozen food aisle. Those doors are closed, no cold air is blowing on you but you still feel that cooling effect, because the cases are colder than your body.”

Beyond the cooling pilot, the MTA is also exploring a largely invisible asset: its dewatering systems. Across Harlem, Bed-Stuy, East New York, and Flatbush, the MTA operates deep wells that continuously pump out groundwater to keep subterranean infrastructure dry. That water flowing at roughly 2,700 gallons per minute at a steady 62 degrees Fahrenheit at the Flatbush site alone per minute at a steady 62 degrees Fahrenheit at the Flatbush site alone lone is currently discharged into storm sewers with no beneficial use. It’s essentially half of a geothermal system, just not connected to anything yet.

At the Flatbush Avenue Brooklyn College terminal station, the 26th hottest in the MTA system, those wells could provide up to 1,600 tons of cooling capacity. The station itself needs only about 300 tons. The excess could serve the surrounding community, including Brooklyn College and the large residential areas to the east.

A note on policy:

Li highlighted two areas where New York could help accelerate this work. First, establishing a market for geothermal renewable energy credits (GRECs), currently only Maryland and Virginia have done so, would spur investment in geothermal and TENS statewide. Second, allowing LL97 non-compliant buildings to offset emissions through GRECs would create a direct financial incentive for building owners to connect to these systems.

Open Discussion: What Does It Take to Get These Projects Built?
Moderated Q&A with Sydney Mainster

Sydney Mainster, moderating from her vantage point as a sustainability leader at one of New York City’s major real estate developers, pushed both panelists on what they need to move these projects forward.

For Koumoullos, the answer was threefold: time to let new technologies mature without losing momentum; an unlocked first pilot project to generate real learning; and continued permission, regulatory, and financial support to keep making small, iterative investments. “I’d love to grab Ricky right now and go look at those pumping stations,” he said. “My eyes light up when I see those, because that’s a thermal resource, that’s a huge opportunity.”

For Li, the most immediate need is to demonstrate success. “It is really hard to convince people that we could recover waste heat from a subway station,” he said frankly. “Three years ago, when we first started socializing this idea at the MTA, people were like, “What do you want to do? We need to run trains.” The East Broadway radiant cooling pilot, he said, will be the proof point that changes that conversation.

Audience questions ranged from workforce implications, panelists noted that while none of the individual technologies in a thermal energy network are new, operating these networks as integrated systems is genuinely novel, to the role of municipal and campus anchor tenants in catalyzing projects. Tighe highlighted the opportunity at Brooklyn College in Flatbush, noting that CUNY institutions have been less represented than SUNY campuses in state-funded TENS work so far.

One exchange stood out: an attendee asked about the 168th Street station, one of the deepest and hottest in the system. Li noted that because of its depth, the station stays very warm even in winter, which makes it an ideal thermal resource for the enormous hospital complex sitting directly above it. He declined to say more about whether conversations with the hospital had already begun, but the knowing smile on his face suggested the answer.

The overarching message of the morning was one of cautious but genuine optimism. New York already has the policy framework, the pilot projects, and — crucially — the thermal resources. What remains is the work of building trust, demonstrating success, and creating the regulatory pathways that allow utilities, transit agencies, and the private sector to act together rather than in parallel. As Tighe put it in her closing remarks: “We can’t just have goals and ideas. We have to turn them into reality.” NYLCVEF will continue to push for that progress, at the PSC, in Albany, and in conversations like this one.

Thank you to our partners

This event was part of our ongoing partnership with Con Edison, fostering dialogue and collaboration among business leaders, policymakers, advocates, and practitioners building a cleaner, more resilient in New York. Thank you also to our panelists Greg Koumoullos and Ricky Li, moderator Sydney Mainster, and our hosts at White & Case LLP.

Noor Malik is a Building Decarbonization Fellow at the New York League of Conservation Voters. She holds a Master of Regional Planning from Cornell University, with a focus on climate adaptation, coastal resilience, and community open space planning. Her project work includes a community resilience plan for Brownsville, Brooklyn addressing urban heat vulnerability, a Soil Reuse Hub proposal for North Brooklyn Neighbors, and a managed retreat and coastal adaptation study for Coney Island. To learn more about Noor and her work, visit her LinkedIn page here.