An example of a 12kW air-source heat pump replacing a gas boiler in a 1930’s four-bedroom semi-detached house in Saffron Walden.
In 2019, we had building work done to add an external office and workshop. This required that the gas boiler and hot water tank be moved, so it was a good opportunity to replace it with an air-source heat pump.
A company from Royston surveyed the house and found that a 12kW system would be adequate to heat the house and extension. The new parts of the house have underfloor water heating, and the older parts radiators, but as the previous gas-based system had been well designed, no radiators needed to be replaced.
The external unit is a NIBE F2040-12, a Scandinavian design so it has no problems heating with cold external temperatures.
It is 100cm high and 115cm wide and placed in front of the house on a car parking space and is generally very quiet in operation.
The installation of a larger hot water tank was required; 300 litres of hot water and a 60-litre buffer tank for the heating system. Its control system is quite advanced, allowing fine tuning and on-line monitoring, though once configured correctly it can run throughout the year without any adjustment or intervention.
Initially we thought it cost neutral to run; it uses about a third to a quarter of the input energy of the gas heating system (the rest being taken from the air) but as electricity is about 3 to 4 times the price per kWh, the overall input energy cost is similar. However, as gas prices have risen more quickly than electricity we think our total energy bills are lower than they would have otherwise been.
We have been very pleased with the result; the house remains warm at an even temperature throughout the year. It was more expensive to install than a replacement gas boiler, but we were able to apply for Renewable Heat Incentive (RHI) payments, which will approximately cover the install costs, paid back over a period of seven years. RHI payments are no longer available, but there are now other grants to support heat-pump installations.