When I got an air-water heat pump for my house, the installer also put in a small electric heater that is connected to the same loop going through my radiators. It is a backup in case my heat pump broke and needed to be serviced. I wouldn't rely solely on a heat pump either. The heater takes 3x the amount of energy to produce the same amount of heat as the heat pump, but since I'll almost never use it (didn't need to turn it on yet), that is negligible and the peace of mind knowing the backup is there is well worth it.