Sure there are. My father recently replaced his oil boiler with an air-source heat pump (from Mitsubishi). It plugs into the same hot water pipework for the rad

Sure there are. My father recently replaced his oil boiler with an air-source heat pump (from Mitsubishi). It plugs into the same hot water pipework for the radiators that the oil boiler was connected to, output temperature is around 60C. Efficiency obviously drops with temperature, but even at -20C it has a COP of around 2, finally shutting down and switching to resistive heating elements at -30C.