They are a supposed to be key weapon in the battle against global warming, by reducing carbon emissions.
But a decision to install air source heat pumps at Reepham High School has, say neighbours, led to pollution problems of a different kind and created a distinctly frosty environment in the town.
Residents who live just metres from the devices - which are used to heat classrooms and other buildings - say they are creating such noise pollution that they are unable to open their windows of use their gardens without being disturbed.
They have lodged complaints with the school and local council but say not enough has been done to quieten the eco devices.
They have also called in local MP, Jerome Mayhew, in an attempt to resolve the issue.
The council and school, however, insist they have already done everything they can to minimise noise from the pumps.
The electrically-powered devices work by absorbing heat from the air.
They are said to be more efficient than gas boilers and can be powered by renewable resources, rather than relying on fossil fuels.
The pumps were installed on land off Whitwell Road last year, and planning permission was only sought afterwards.
The nearest homes, on Broomhill Lane, are only around 5m away from the pumps, and problems began shortly after the pumps started whirring.
In an email to Broadland District Council, seen by this newspaper, one resident wrote: "There is an increase in the noise nuisance this proposal creates and it has a detrimental effect on our amenity spaces.
"This is a comedy of errors which [the council] should be ashamed of."
Mark Bridges, who lives nearby and is a long-term campaigner of local issues in Reepham, said: "They are very noisy. They are a 24-hour noise nuisance."
He blamed the council for allowing the pumps to be installed in the first place, without being able to reduce the noise pollution.
He said there were "cheaper, more efficient" schemes which should have been considered.
Locals say they were assured the pumps would be switched off on bank holidays and during the school holidays, but they claim they have been left running.
Mr Mayhew said: “Whilst I welcome the school’s efforts to reduce the carbon impact of their heating system, this needs to be done in a way that is considerate to their neighbours and compliant with the planning system.
“I will continue to help local residents to make sure their concerns are properly considered."
The council said it had investigated the complaints and monitored the noise made by the pumps.
A spokesman said: “The council has been working with all parties to get to a position that has enabled matters to move forwards.
“Noise testing of the pumps has been carried out and concerns and complaints have been investigated by the council’s Planning Enforcement Team.
“The proposals which provide an alternative source of renewable energy to the school will reduce the reliance on centralised, non-renewable energy sources and make a positive contribution towards achieving green energy targets, tackling the challenges of climate change and reducing the reliance on finite energy sources.”
Reepham High School and College head teacher, Tim Gibbs, said: “While I am sympathetic to the complaints raised by our neighbours, we have responded to all of their concerns and remain compliant in everything we have done with the installation of the air source heat pumps."
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