A public housing project in Paris plans to reduce its carbon footprint by harnessing a universal and completely renewable form of energy: excess body heat.
Paris Habitat, the city’s largest owner of low-income public housing, will redirect heat from underground passages in the subway to heat exchangers and pipes that warm one of its properties on rue Beaubourg. A stairwell currently connects the building to the subway station, and heat from the train tracks and sweaty commuters keeps that corridor between 57 to 68 degrees—even in winter.
“We were lucky to find a passageway that allows us to collect the heat directly from the metro, without having to pay to build one, otherwise it would have been impossible,” Francois Wachnick told Reuters. He hopes the project will slash the building’s carbon emissions by one-third.
It’s not a new concept. Minnesota’s Mall of America already recycles heat generated from shoppers’ bodies to supplement its heating system during the brutal winter months. TIME’s crack reporter Tara Kelly recently visited Stockholm where engineers have devised a system that uses passengers’ body heat to warm underground water tanks. That water is then pumped into a 13-story building located 100 yards away.