AFAIK it's not ideal but possible to use existing radiators. My parents recently added an air heatpump to their existing (wood) heating system without changing

AFAIK it's not ideal but possible to use existing radiators. My parents recently added an air heatpump to their existing (wood) heating system without changing radiators. They Installed a new boiler (water tank, not sure about the translation) where the top half is heated by the heat pump and they can optionally heat the whole tank using the old wood heater.