Hundreds of thousands of homes are to be heated using warmth generated by industrial machinery, geothermal energy and even Tube trains, under government-backed plans for a major expansion of “heat networks”. More than a third of local authorities in England and Wales are now working on new schemes that transport heat from one source through pipes to hundreds of homes or businesses, according to figures obtained by The Daily Telegraph. About four in five homes are currently heated by gas-fired boilers but they will have to be replaced by greener forms of heating if Britain is to hit its climate change targets, which require carbon emissions to be slashed by 2050. Heat networks – effectively giant central-heating systems, which can supply entire neighbourhoods – are seen as one way of achieving this. They use insulated pipes to transport hot water or steam to homes, where it warms up the mains water supply through a “heat exchanger” unit. Ministers set up a “heat network delivery unit” in 2013 to award funding for the development of new schemes, and this week are due to announce the 38 councils that have won the latest £2.8m tranche to work on feasibility studies. This will bring the total number of local authorities working on such plans to 131, out of the 381 in England and Wales, with more than 200 individual projects in the offing. Many networks use heat produced by burning gas to generate power in “combined heat and power” plants. Although not zero-carbon, they are significantly more energy-efficient than letting the heat go to waste, and can offer a cheaper source of heat than everyone using individual domestic boilers.