DEEP in the tunnels of the London Underground, as in many subway systems around the world, it's so hot it feels like hell. And yet in a basement only a few metres away, a boiler is firing to heat water for someone's shower.

Rather than stewing in our excess heat, what if we could make it work for us? There is no shortage of waste heat, after all. Throughout our energy system – from electricity generation in a power plant to boiling a kettle, using boilers to warm houses to powering a car – more than 50 per cent of the energy we use leaks into the surroundings as wasted heat.

Recapturing it wouldn't just benefit our wallets. It would reverse some of the damaging effects that waste heat from our towns and cities is having on the climate.