Homeowners Professionals
Air and geothermal

Kingston Lacy Case Study

Future-proofing heritage through renewable heating

Kingston Lacy

As Europe’s largest conservation charity, the National Trust views climate change as the single biggest threat to the precious landscapes and historic houses it cares for.  Launched in 2013, its National Renewables Investment Plan is one important aspect of a wider programme of activity aimed at reducing the charity’s carbon emissions to net zero by 2030. As well as helping to reduce negative environmental impacts and improve energy security and business resilience, the money saved by being more energy efficient goes towards vital conservation work that protects the countryside and the wildlife that depends on it.

The first phase of the plan saw the installation of 138 renewable energy projects within nine years. For phase two, the Trust is turning its attention to reducing fossil fuels at 100 of the highest-emitting buildings it looks after.  

One such property is Kingston Lacy in Dorset, a 17th century Venetian mansion set in idyllic countryside and filled with remarkable antiques, including one of the UK’s finest private collections of paintings. Protecting these valuable artefacts and minimising impact to the buildings and historic gardens were key considerations of this substantial and fastidious retrofit project.

Time for a change

Kingston Lacy’s heating system is critical to the conservation of the house and its contents. It was previously heated by two 87 kW oil-fired boilers which were estimated to be around 20 years old, less than 75% efficient and approaching the end of their operational life.  

The mansion was the fifth highest oil-consuming property in the National Trust’s Southwest portfolio, using 30,000 litres of oil (325,000 kWh) and releasing about 80 tonnes of carbon a year.  

The 10,000-litre oil storage tank was also in poor condition, risking environmental contamination.

Ground source heat pump - the perfect fit

From the outset, a heat pump was the preferred solution to replace the ageing and outdated heating system. The heat pump’s ability to provide stable balanced heat would be much better for the sensitive collections at the Grade 1 listed property than the fluctuating high temperatures of a fossil fuel boiler. Using a heat pump with weather compensation controls to reduce energy used in correlation to rises in external air temperature, also meant the National Trust would be able to heat the mansion for longer periods, helping to control humidity and secure this beautiful place for future generations.

Renewable energy consultants Redcotec and installation contractors ISO Energy together recommended a ground source heat pump due to the low visual and operational impacts involved.  

In order to cover the whole heating load of all the property’s main buildings, four 42 kW Viessmann Vitocal ground source heat pumps were specified for use together with a Grundfos TPE2 80-270 circulation pump, two 1,000-litre buffer tanks and two brine expansion vessels. ISO Energy dug thirty-two 180 metre bore holes in order to install vertical heat-harvesting ground loops. Non-toxic glycol was used as the thermal transfer fluid.  

“The Vitocal heat pump was selected because it could provide the high temperature needed for this project, as well as being highly reliable, hard wearing and efficient,” said William McCarthy, Senior Consultant at ISO Energy. “It also came with a seven-year extended parts warranty.”

The new system was part-funded by Low Carbon Dorset as part of the European Regional Development Fund. Generating around 289,000 kWh of energy, it will save around 25% each year on fuel costs and reduce emissions by about 84%.

Meticulous care

The GSHP sits right at the heart of the Kingston Lacy estate amidst historic buildings and beautiful listed gardens. It was essential that the greatest possible care be taken during the installation to prevent any damage to the buildings’ fabric and contents, and to minimise any changes to fixtures and fittings. ISO Energy also ensured the impact of external works to the registered gardens was minimised and the landscape reinstated effectively.  

As Kingston Lacy is a living, working community, accommodating staff, visitors, tenants and holiday lets, a smooth transition to the new system with minimal disruption was essential.

“Hopefully this large and successful installation in such a spectacular setting helps to dispel the myth that heat pumps don’t work in old properties,” said McCarthy. “Correctly designed and specified, they can be highly effective.”


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 that you get from fossil fuels. It means we have a more stable environment that reduces the likelihood of mould growth and insect infestation.”

System Spec

  • 42 kW high-temperature Viessmann Vitocal Ground Source Heat Pump x 4
  • Grundfos TPE2 80-270 circulation pump
  • 32 x 180 metre boreholes
  • Glycol (thermal transfer fluid) non-toxic/hazardous
  • 1,000 litre buffer tank and brine expansion vessel x2
  • 4 metre UNO 75/75 Pre-insulated distribution pipe x2

Groundworks materials:  

  • 40 mm headering pipe work
  • 8-port manifold x4
  • manifold pit and chamber x4
  • 125 mm reverse return and flow and return pipe from manifold pits to plantroom


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