If you often take the train at the underground subway station during rush hour, you’ll probably have noticed that it’s incredibly hot and stuffy. The builders of a new housing estate in Paris have come up with a rather innovative idea to harness this waste heat and use it to generate energy for a low-income housing building located above the station. The high temperature in the station is a result of the energy expelled by each passenger and heat produced by the moving trains. This unique heating system aims to cut carbon dioxide emissions by a third, compared to using a traditional boiler room. This experimental project is slated to be completed in 2011.