alan_m wrote:

Andy Burns wrote:

The electricity costs for a heatpump will be about 85% of the cost for
mains gas, but the installation costs are much higher.

Is that figure for ground sourced or air sourced heat pumps?

ground source.

From my back of envelope previous investigations, an air sourced pump
can give 3kW thermal energy for every 1kW of electricity but as the
outside temperature falls to 0C this efficiency also drops to more like
2KW thermal per 1KW.

yes COP falls with temperature, but 1m below ground coils don't get as
cold as air, unless coils are undersized and you end up freezing the
ground by over-extracting.

Installing an EFFECTIVE heat pump system also depends on the level of
insulation in the home

as I said, poke some answers into the calculator.

It may work extremely well for a new build where you can specify the
quality of the build and insulation.

Can still be marginal ...