It's worth noting that the temperatures at which heat pumps function well is more of a design choice than a fundamental limitation. You can make a heat pump whi

It's worth noting that the temperatures at which heat pumps function well is more of a design choice than a fundamental limitation. You can make a heat pump which functions down to -20C with HFC refrigerants, maybe lower with some other types. However, you may choose to optimize 'mild weather' performance by forgoing low temperature performance. Modern heat pumps work pretty darn well across a range of temperatures. What we really need are heat pumps which do not use HFC refrigerants - they are a pretty significant cause of global warming, and there are other options (CO2 being one of the best, in my opinion). https://www.drawdown.org/solutions/materials/refrigerant-management https://www.drawdown.org/solutions/materials/refrigerant-man...