A 300-year-old country mansion is to get environmentally-friendly heating from the ocean with the UK's biggest marine source heat pump, the National Trust said.
The technology installed off the North Wales coast will provide all the power needed to heat the National Trust's Plas Newydd mansion, which sits on the shores of the Menai Strait looking across the mountains of Snowdonia.
The 18th century stately home was the Trust's biggest oil consumer, using around 1,500 litres of oil on some winter days.
Now it is switching to a £600,000 marine source heat pump, which will use sea water pumped to a heat exchanger onshore to create the heat needed to warm the entire house.
The 300-kilowatt marine source heat pump, one of the first such systems in the UK and the biggest, according to the National Trust, is expected to save the charity £40,000 a year in costs for Plas Newydd.
It is the first of five schemes being completed in a £5.3 million pilot phase of the Trust's renewable energy investment programme.
If the five pilot schemes are successful, the National Trust plans to invest in 43 renewables projects at the places it looks after, as part of commitments to reduce energy use by a fifth, halve fossil fuel consumption and generate 50% of its energy from renewables.
Adam Ellis-Jones, assistant director for operations in Wales at the National Trust, said: "With the Irish Sea right on the doorstep of Plas Newydd, a marine source heat pump is the best option for us.
"However being a pioneer is never easy. There are very few marine source heat pumps and none of this size in the UK, so it has been a challenging project but an exciting one."
He said the Trust worked closely with coastal and marine experts and conservationists to get the best from the technology while protecting the fragile environment and archaeology of the site.
Patrick Begg, rural enterprises director at the National Trust, said: "It's clear to us that we need to make big changes so that we can continue to protect our treasured places and tackle the impact of climate change.
"This successful scheme marks a major step forwards in our clean energy journey."
The other pilot schemes being developed by the National Trust are a biomass at Croft Castle, Herefordshire, a woodchip boiler for Ickworth in Suffolk and hydro-electric projects at Hafod y Porth in Snowdonia and Stickle Ghyll in the Lake District.
The renewable investment programme has been launched in partnership with renewable energy supplier Good Energy.
The company's chief executive, Juliet Davenport, said: "This project shows that cutting-edge British renewable technology can transform the energy use of some of our oldest buildings."