I'll add that modern heat pumps can work effectively in heat pump mode (around 4kW of heat out for every 1kW of electricity in) down to around -25c. Below that

I'll add that modern heat pumps can work effectively in heat pump mode (around 4kW of heat out for every 1kW of electricity in) down to around -25c. Below that they will automatically switch to resistive heating (same as baseboard heaters). I'm building a new house in Northern Europe (it regularly gets to -25c/-5F in winter) and will we be using a Daikin Altherma 3R air source heat pump to provide hot water, underfloor heating, and air conditioning - all from a single heat pump.