London Underground air used to heat homes above ground
If you've travelled on the London Underground you'll know how hot it can get. But what if the stifling air could be put to good use?
At Islington's derelict City Road station, a huge fan extracts warm air from the Northern Line tunnels and sends it to an energy centre above ground.
It is used to heat water that's pumped to 1,350 homes, a school and two leisure centres.
Transport for London claims the Bunhill 2 Energy Centre is the first of its kind in the world, and is assessing whether 56 other ventilation shafts have potential for exporting waste heat.
Video by Jamie Moreland