Modern heat pumps drive the VFD and circulation pumps as needed (i.e. the pumps run slower when the heat demand is low). The main factor for good efficiency is

Modern heat pumps drive the VFD and circulation pumps as needed (i.e. the pumps run slower when the heat demand is low). The main factor for good efficiency is low output temperature- underfloor heating works at ~35 deg C, radiators work at ~55 degC (because of smaller surface area). I sized my heat pump based on historical data of heating oil /diesel consumption- since I had the data of past two winters, I could reliably determine the maximum continuous heat requirements for my house.