After installing a solar thermal collector and a PV array on their south–facing roof, the owners of this 4-bedroom detached house were keen to complete their transition to a fully renewable heating and hot water system by installing a heat pump to replace their aging oil-fired boiler.

The oil boiler supplied heat to wall-mounted radiators at a flow temperature of +70°C. We calculated the additional radiator capacity that would be needed to allow the heat pump to operate at a lower design flow temperature of 50°C, and replaced some of the existing radiators with new double radiators with larger surface areas.

We installed a 12kW NIBE F2040 air source heat pump on the flat roof of the garage. This uses an inverter-driven compressor which modulates its output to match heat demand, using an external sensor to calculate the required flow temperature (weather compensation). At a flow temperature of 50°C it achieves a Seasonal Coefficient of Performance (SCoP) of 3.44, although, depending upon the weather, for much of the time it will operate at lower flow temperatures and achieve a higher SCoP.