Over the years Kingston Lacy, which was built to resemble a Venetian palace that has materialised in the English countryside, has been kept warm and dry with open fires and coal and oil boilers.
Now a “pioneering” ground source heat pump has been installed to protect the spectacular Dorset country mansion and its collection of paintings by masters such as Velázquez, Titian and Rubens.
The new system should help preserve the art collection by providing a steady, gentle heat without spikes and dips in temperature, as well as saving 30,000 litres of oil each year.
It is one of the National Trust’s biggest heat pump projects to date, and the first high-temperature ground source system the charity has installed.
The old oil tank has been replaced by almost 6,000 metres (19,685ft) of underground pipes, which transport natural ambient heat in the ground to four high-temperature heat pumps, that in turn warm the 17th-century mansion house and courtyard buildings.
The installation of the pipework involved drilling 32 vertical boreholes in an overflow car park, with each hole 180 metres deep.
Specialists spent two years conducting extensive archaeological and ecological surveys to ensure the protection of the historic parkland, which includes iron age hillforts, heathland and water meadows.
As well as saving approximately 57 tonnes of carbon a year, the new heating system will remove the danger of oil spills from the previous boilers and storage tank.
The trust also says the heat pump will improve conservation of the building and its collection by stabilising the temperature and humidity levels.
Known as the “palace of art”, the house has an extravagant Spanish Room that the estate’s 19th-century creator, William John Bankes, designed from exile after he was forced out of Britain because of his gay relationship with a soldier, and his collection of ancient Egyptian artefacts, the largest private collection in the UK.
Owen Griffith, the lead renewable heat project manager for the National Trust, said: “Even in the most historically significant settings like Kingston Lacy, it’s possible to integrate these modern technologies.
“Not only will the heat pump reduce the property’s dependency on fossil fuels, but it’ll create a safer environment and improve conditions for the collection items here.
“Magnificent buildings like these have been around for centuries, but their heating systems have evolved – from open fires to coal boilers and then oil boilers, with many energy innovations along the way. This is simply the next step in Kingston Lacy’s history and preservation.”
Griffith added: “What we’ve found when we’ve moved from fossil fuel conservation heating to heat pump conservation heating is that extending the heating time means that we have a longer duration of lower-grade heat coming into the building so it’s a lot gentler. We’re able to stabilise the internal environment over a longer period so daytime/night-time fluctuations, for example, are balanced out.
“You don’t get the spikes in heat from that you get from fossil fuels. It means we have a more stable environment that reduces the likelihood of mould growth and insect infestation.”
