Plas Newydd: Heat from the sea to warm historic house
22 May 2014 Last updated at 17:48 BST
Heat from the waters of the Menai Strait will be used to heat a historic north Wales mansion in a bid to cut costs.
The new heat pump at Plas Newydd relies on a heat exchanger, which uses a system similar to refrigeration to amplify warmth from pipes in the sea.
The 300kW marine source heat pump cost the National Trust £600,000 and is expected to save around £40,000 a year in operating costs.
BBC Wales environment reporter Iolo ap Dafydd reports.