Could London Underground waste heat warm homes? New York study tests subway geothermal network

New York City’s Metropolitan Transportation Authority has launched an $800,000 feasibility study to determine whether excess heat from subway platforms can be captured, stored and reused to warm nearby municipal buildings. The concept, known as a Thermal Energy Network, could offer lessons for other cities with ageing underground rail systems — including London, where deep-level Tube platforms regularly reach uncomfortable temperatures even in winter.

The MTA study will test the technology at the Brooklyn Bridge-City Hall and Chambers Street station complex on the 4/5/6 and J/Z lines. The project will use radiant cooling panels and geothermal boreholes to absorb heat from platforms during summer, store it underground, and release it into adjacent buildings during colder months. The MTA estimates the process could be up to 35 per cent more energy efficient than conventional air conditioning.

Key facts
| Element | Detail |
|—|—|
| Study cost | $800,000 (approximately £625,000) |
| Test location | Brooklyn Bridge-City Hall / Chambers Street station complex, Manhattan |
| Technology | Thermal Energy Network with geothermal boreholes and radiant cooling panels |
| Primary benefit | Reduced platform heat in summer; recycled heat for nearby buildings in winter |
| Efficiency claim | Up to 35% more energy efficient than air conditioning |

How the Thermal Energy Network works

Thermal Energy Networks, or TENs, are district-scale heating and cooling systems that move heat between buildings rather than generating it from scratch. In the New York proposal, heat absorbed from subway platforms during summer is transferred via chilled water circulating through panels and embedded tubing. The heat is then stored in geothermal boreholes — deep vertical wells drilled into the earth — and drawn back up during winter to heat nearby municipal buildings.

The approach differs from conventional heat pumps or electric resistance heating because it reuses existing waste heat rather than burning fuel or consuming grid electricity for heat generation. Several hospitals and universities in the United States already operate TENs on a smaller scale, the MTA noted.

For the MTA, the immediate motivation is passenger comfort. New York City subway platforms can become dangerously hot during summer heatwaves, with temperatures on some lines exceeding 40°C. The problem has drawn increasing attention as climate change drives more frequent and intense heat events. The study will measure how much cooling the panels can deliver at platform level and calculate the potential energy cost savings for the city.

Why London Underground faces a similar problem

The London Underground faces a comparable — and in some respects more severe — challenge. Deep-level Tube lines such as the Central, Bakerloo, Piccadilly, Northern and Victoria lines were built more than a century ago with little ventilation provision. The tunnels act as heat traps: trains, braking systems and passenger body heat all contribute to rising temperatures, and the surrounding clay soil retains heat rather than dissipating it.

Summer platform temperatures on the Central line have been recorded above 35°C, and the problem is not limited to hot weather. The deep tunnels remain warm year-round, with winter temperatures on the Central line frequently exceeding 25°C. Transport for London has installed air cooling on the Victoria line and is trialling passive ventilation shafts on the Bank branch of the Northern line, but full air conditioning on deep-level trains remains technically difficult because the tunnel space is too narrow to accommodate the necessary equipment.

TfL has explored waste heat recovery in limited contexts. The Bunhill Heat and Power network in Islington, which uses heat from the London Underground’s Northern line tunnels to warm local homes, is one of the few operational examples. That scheme, delivered in partnership with Islington Council, captures heat from ventilation shafts above the tunnel and distributes it through a district heating network to approximately 1,350 homes and community buildings.

The New York study is more ambitious in scope: it aims to capture heat directly at platform level, store it seasonally in geothermal boreholes, and serve multiple municipal buildings from a single network. If the MTA study proves technically and economically viable, the model could be adapted for London stations where deep-level tunnels run beneath large public-sector building clusters — for example around King’s Cross, Paddington or Bank.

What the study will measure

The MTA study, led by the authority’s sustainability and resilience division, will assess three main variables: the amount of heat that can be extracted from platforms without causing condensation or structural issues; the efficiency of seasonal heat storage in geothermal boreholes under urban conditions; and the capital and operating costs of retrofitting TENs into existing stations.

The study is expected to run for 12 to 18 months and will produce a feasibility report rather than a construction commitment. The MTA has not disclosed whether it intends to build a full-scale system if the study succeeds, but the agency has included TENs in its broader climate resilience planning.

The New York City Department of Citywide Administrative Services, which manages the city’s municipal building portfolio, will participate in the study to identify potential building connections. If the scheme proceeds, the heat would serve city-owned buildings such as schools, libraries and administrative offices within a quarter-mile radius of the station complex.

Relevance for London planners and policymakers

For London-based readers, the New York study offers a concrete test case that could inform TfL’s own heat management strategy. The London Underground currently spends an estimated £50 million to £60 million per year on tunnel cooling and ventilation, much of which is consumed by fans, pumps and the Victoria line’s active cooling system. If TENs could offset even a fraction of that cost while generating a revenue stream from heat sales, the business case could be attractive.

The technology also aligns with the Mayor of London’s climate targets. The London Environment Strategy commits the city to reducing greenhouse gas emissions to net zero by 2030, and district heating networks are identified as a key tool for decarbonising heat supply. The Greater London Authority’s London Heat Map, which identifies areas with high heat demand and potential waste heat sources, already shows clusters of public-sector buildings above many Tube stations.

A practical constraint is the London Underground’s fragmented ownership and governance. TfL operates the Tube network, but the stations are owned by TfL and the land above them is often in separate ownership. The New York study benefits from the MTA and New York City being able to coordinate across municipal buildings and subway infrastructure under unified governance. In London, any TEN scheme would require coordination between TfL, the relevant borough council, the GLA and potentially private landlords.

What remains unknown

The MTA study has not yet published baseline temperature data for the test station, nor has it specified the expected capital cost per station. The $800,000 study budget is modest relative to the cost of retrofitting a station with geothermal boreholes and radiant panels, which could run into tens of millions of dollars per station if the technology proves viable.

It also remains unclear whether the system can operate effectively in London’s geological conditions. The clay soil beneath central London has good thermal storage properties, but it is also highly shrinkable and prone to subsidence when dried out by heat extraction. Geothermal boreholes in London clay require careful engineering to avoid ground movement affecting nearby foundations, tunnels and utilities.

The MTA study will not address the question of whether TENs can reduce platform temperatures enough to meaningfully improve passenger comfort. The radiant cooling panels remove heat from the air, but they do not lower humidity, which is a major contributor to discomfort on deep-level platforms. The study’s primary metric is energy efficiency rather than passenger thermal comfort.

Source: Planetizen News, “NYC’s sweltering subway tunnels might soon provide heat to nearby buildings”, August 18, 2026. https://www.planetizen.com/news/2026/08/138235-nycs-sweltering-subway-tunnels-might-soon-provide-heat-nearby-buildings

Datos clave