HOMEOWNERS and firms who switch to sustainable fuels to heat their properties will be able to reclaim part of the cost from the taxpayer under a ?4.5 billion government scheme to be launched this week.  The Renewable Heat Incentive (RHI) will offer subsidies for various kinds of green heating technology including boilers that run on wood chips, solar panels for heating water, groundand air-source heat pumps and the production of methane from sewage.  Households and firms installing, for example, an approved wood-chip boiler will be able to claim payments for generating "green" heat. These could halve their heating costs.  Heating accounts for about 47% of Britain's CO2 emissions, so switching away from fossil fuels is vital to achieve carbon reduction targets.  Greg Barker, the climate change minister, who is overseeing the scheme, said he hoped it would reduce reliance on imported fossil fuels, particularly amid fears Middle East turmoil will send oil prices soaring.  "The aim is to help new technologies get started in the face of competition from established energy sources like gas and oil," he said. "We are offering long-term support until at least 2020 so the manufacturers know just where they are."  Introduction of the scheme, the first of its kind in the world, follows a campaign by Friends of the Earth and the Renewable Energy association (REa).  Leonie Greene, the REa's head of external affairs, said it could be a "breakthrough moment for renewables".  She added: "If the levels of support are right, it will empower people to change how they heat their homes, schools and workplaces, while also generating thousands of new jobs in green industries."