Government plans to subsidise green heating are challenged today by the largest ever field study of “heat pump” devices in the UK, which reveals 80% perform so badly they would not qualify as renewable energy under proposed European standards.

The report, from the Energy Saving Trust, reveals the prevalence of badly installed heat pumps that are consequently under-performing. The controversial report could affect the government’s plans to launch its Renewable Heat Incentive (RHI) next April to pay householders for generating heat from such “green” ground and air source heat pumps. There are already fears the RHI could be a victim of spending cuts announced next month.

Unlike other sources of renewable energy, such as solar photovoltaic panels and wind turbines, heat pumps require a certain amount of electricity to create energy. They work like a refrigerator in reverse, using a coolant gas to transfer heat from outside air or soil into a building. Electricity is needed to pump and compress the gas, which also allows it to generate higher temperatures than those outside. Air source pumps typically look like oversized air-conditioning and are place outside homes, while ground source ones involve loops of plastic tubing laid underground. Theoretically they should generate more energy than they consume.