A proposal to warm buildings by using heat generated by water treatment processes is set to move to the next stage after it was given the go-ahead by Hounslow Council’s Cabinet.
Published: Friday, 28th March 2025
Councillors have approved a request to apply for up to £11m of funding from the Green Heat Network Fund. If granted the money will be used to work up detailed plans and, crucially, to subsidise what would be a £53m project that could be ready as early as 2029.
Once operational, the Hounslow Heat Network scheme would extract heat from water warmed by the treatment process at Mogden Sewage Works in Isleworth.
Cabinet Members heard that the final treated water is typically about 20oC as it leaves the works to be discharged into the Thames.
Heat is extracted from this using a heat pump and transferred to clean water which is circulated to buildings in buried insulated pipes. Each building has a heat exchanger, which transfers heat from the heat network pipe to its own heating system, much as a gas boiler would heat the water.
An added advantage to this process, is that the final effluent discharged to the Thames is thus cooler than it would have been, making it better for the environment.
The energy supplied by the network will initially heat around 30 major buildings, including those at the West Middlesex Hospital, workplaces, public buildings and large residential blocks, and could slash carbon emissions by as much as 75 per cent compared to gas boilers.
The decision has been hailed as an important step towards achieving the Council’s climate ambitions and would result in cleaner air by replacing gas boilers with heat exchangers connected to a heat network - gas boilers are a major source of nitrous oxide pollution, which can lead to respiratory issues.
Councillor Katherine Dunne, Hounslow’s Cabinet Member for Climate, Environment & Transport, said it paved the way for more efficient heating in the borough. She said:
Many buildings still rely on gas and we have seen very recently that can put us at the mercy of hugely expensive cost spikes in, even before we take account of the cost to the environment.
This is certainly the lowest cost option for low carbon heating and there is absolutely no reason why we shouldn’t be doing it. This is tried and tested technology used extensively in Scandinavian countries for decades.
For now, it’s too early to say if implementation will mean cheaper bills, but we believe it offers some protection against the wild fluctuations in energy prices that we’ve seen in the past few years.
Eventually, we would like to consider rolling out the heat network to other areas of the borough.
