It depends on your radiators and insulation. As a rule of thumb modern air-to-water heat pumps have a good efficiency up to a water temperature of 55 C. That ca

It depends on your radiators and insulation. As a rule of thumb modern air-to-water heat pumps have a good efficiency up to a water temperature of 55 C. That can be enough if you have radiators with a large enough surface and no terrible insulation.