Converted Napoleonic fortress with cinema and swimming pool cuts running costs and carbon-pollution with air source heat pumps

Project Overview

One of the most exclusive properties in Jersey, Le Couperon is an £8 m luxury home overlooking Rozel Bay with private access to the beach. On the site of a converted Napoleonic fortress and developed from a former hotel, this is an ‘upside down’ property with bedrooms downstairs and main living rooms upstairs. Floor-to-ceiling windows make the most of the views over the top of the fortress’ stone walls and across the bay.

Le Couperon boasts an open plan living room, kitchen and dining room, five bedroom suites, home office, temperature-controlled wine cellar, 12-seater American-style cinema room, gym, six-car garage with underfloor heating and two separate guest units. An infinity pool is located to create the illusion of flowing into the sea.

After specifying the highest standards in all other aspects of the building, the property developer did not want to compromise on the space and water heating. The heating system of the former hotel, with 40-year-old cast iron boilers, was expensive to run and in need of refurbishment. Heating had to be provided to the main house’s considerable, 11,500 sq ft floor area, swimming pool, showers, and guest accommodation. The new heating system had to be strong, dependable, precisely controllable in different parts of the house, exceptionally energy efficient, and environmentally friendly, with no use of fossil fuels.

Meeting the demand for precisely controllable fossil-free heating

The optimum heating technology for this property was determined through a process of elimination. Biomass boilers were ruled out as fuel would have to be imported, ground source heat pumps excluded because of drilling limitations, and solar panels resisted because of their effect on the aesthetics of the building. The solution, for energy-efficiency and fossil fuel-free heating, was three Viessmann Vitocal air source heat pumps. Viessmann’s heat pumps have a marine-grade coating, ensuring they are resistant to corrosion in the salty sea air, and their large heat exchangers minimise wear and tear in such conditions.

Two 20 kW Vitocal 350-A heat pumps were installed by Viessmann trained installer Matrix Energy Systems to provide heating and hot water for the main house, with another 14 kW Vitocal 350-A for the gym, swimming pool, showers, and staff/guest accommodation. An 18 kW immersion heater was fitted as backup.

The heat pumps feed their energy to an underfloor heating system on both floors of the house, where temperature is monitored and controlled by wall-mounted thermostats in 30 different zones. The system has three weather compensation controls, enabling it to adjust to changing climatic conditions, and hot water is circulated around the system at controlled intervals to prevent wasting energy or water.


This generously sized house is heated efficiently and cost effectively. Heating bills have been reduced to less than half of the previous level, cut from £5,800 to £2,700 per year. For the production of 75,000 kWh (75 m watt-hours) per year, this is exceptionally economical.

A great improvement has also been achieved in the environmental friendliness of this building on its beautiful seaside site: the previous, oil-fired heating system’s output of 23.8 tonnes of carbon per year has been halved.

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