A website, heatpumpmonitor.org, external features real-time results from 12 homes around Britain, including Mr Wall’s. The data is processed via OpenEnergyMonitor, a digital platform that allows people to track their household energy consumption.

Heat pumps work by absorbing a small amount of heat from the outdoors into a refrigerant, the fluid that circulates within the device. A compressor then pressurises the refrigerant, increasing the temperature, and heat is subsequently passed on into the house.

A well-installed heat pump might get three kilowatt hours (kWh) of heat for each kWh of electricity it consumes. This ratio is called the coefficient of performance, or COP – the higher it is, the better. Heat pump-watchers tend to use this figure as a means of judging how well their device is working, sometimes in friendly competition with other heat pump owners.

The COP varies depending on things such as the weather or how hot you choose to have your radiators.

“Right now it’s 4.5,” says Mr Wall, excitedly. “It’s six, seven degrees [Celsius] outside here and I’m getting 4.5.”

A COP of 3 or above is deemed very good because it means that the cost of running the heat pump should be cheaper than, external a gas boiler, for the equivalent heat output – depending on energy tariffs.

There are caveats, though. Mr Wall did have to spend thousands on upgrading radiators and pipework in his house, among other adjustments, before he decided it was heat pump-ready.

He chose an air source heat pump that draws heat from the air, even when it is very cold outside, and adds that it is important for the device to be correctly sized and installed, to ensure it runs efficiently. His solar panels also help him to reduce how much he pays for electricity.