Over here air-water heat pumps have become quite popular for replacing old oil boilers, as you can keep using the existing water pipes and radiators. I don't th

Over here air-water heat pumps have become quite popular for replacing old oil boilers, as you can keep using the existing water pipes and radiators. I don't think they're that common in new construction. My father recently did exactly that, installing a unit by Mitsubishi. IIRC it has a COP of 2 at -15C, finally switching to resistive heating at -25C or so (which is somewhat unusual, maybe a few days or a week per year over here). He also has his old wood boiler as backup that he uses when it gets cold (it was a dual oil/wood boiler, though the oil burner and oil tank was ripped out as part of the retrofit).