A million properties across England could in future be heated by water from rivers, canals and the sea, the government says.
The Department for Energy calculates this is the potential of a technology known as the water source heat pump.
This relies on a heat exchanger, which uses a system akin to refrigeration to amplify warmth from pipes in the sea.
If the energy from the process comes from renewables, properties can be warmed with near-zero carbon emissions.
The government’s water source heat map identifies more than six gigawatts of potential low-carbon heat.
One major project – at the National Trust’s historic Plas Newydd house in Anglesey – is already running.
The heat pump system works best in well-insulated buildings because there is a large energy cost in warming the water to the level normally used in central heating radiators.
In the case of Plas Newydd it is ideal because the Trust doesn’t want the house to get too hot.
The 300kW marine source heat pump cost the Trust £600,000 and is expected to save around £40,000 a year in operating costs.
At Plas Newyydd, pipes have been laid into the Menai Straits, the narrow stretch of water which separates the island of Anglesey from mainland Wales.
The pipes are filled with a refrigerant heat transport chemical. The fluid extracts heat from the sea and releases it into the heat pump.
The fluid is compressed to increase the temperature further to heat the property. The pressure of the fluid is then lowered via an expansion valve and the process starts again.
A National Heat Map will be published at the end of June, showing the rivers in England that have the highest potential for water source heat pumps.
The map refers only to England, but DECC is in discussions with Scotland, Wales and Northern Ireland on the issue.
PHOTO: Water pipes had to be laid to extract the water from the sea and transport it to the heat exchanger.
CREDIT: BBC.