A historic National Trust property near Truro has saved 64 tonnes of carbon a year after installing a new heat pump system. 

Trelissick, an 18th-century mansion with sprawling gardens in Feock, upgraded its old-fashioned oil boilers to ground source heat pumps last autumn. The 165kW system has been heating the draughty Grade II* listed building ever since, as well as the estate’s bookshop and cafe. 

The National Trust used a mix of grants and government funding for the retrofit, taking the charity one step closer to its goal of becoming carbon net zero by 2030. 

The system was designed by Chasewater company Kensa Heat Pumps, which installs more than half the UK’s ground source heat pumps each year. 

The system harnesses natural heat from underground, saving the property tonnes of carbon a year. During the Great Big Green Week in June, visitors were able to tour Trelissick’s basement, where the heat pump system is housed. 

The house must be kept at a certain temperature to preserve the fabric of the house, yet with no double glazing or insulation in the walls, doors, windows or roof, heat escapes easily.

After the retrofit, however, Trelissick’s carbon footprint was reduced by 64 tonnes, while bills have stayed relatively stable in a volatile energy market. Dan Roberts, technical director at Kensa Heat Pumps, said: “Trelissick was retrofitted with a 165kW ground source heat pump system to replace the old oil boilers, providing the property with 100 per cent of its heating and hot water year-round and reducing carbon emissions. All the infrastructure is underground so the outside of the property itself is completely unaffected. It’s a fantastic example of how historic buildings can benefit from low carbon heating.”

Improving the energy efficiency of properties built before 1919 could reduce carbon emissions from UK buildings by five per cent each year, according to a recent report from the National Trust, Historic England and leading property organisations. Retrofitting the UK’s old buildings could also generate an extra £35bn in new money, the report adds. 

Gareth Lay, general manager for the National Trust’s Heart of Cornwall portfolio, said: “This was a fantastic project that has allowed Trelissick to move away from its reliance on fossil fuels for heating.”