Abstract The use of pre-set thermostatic radiator valves (TRVs) contributes to the reduction of energy consumption and the increase of the energy efficiency of the existing heating systems in buildings. However, there are limited long-term experimental studies that document the level of energy savings achieved by the use of TRVs, quantified for three different options of their utilisation. Long-term field data were collected over several heating seasons from nine existing multifamily residential buildings organized into three groups characterized by different modernization activities using TRVs. The first group includes the cases where the buildings are equipped with TRVs without hydraulic balance of the heating system with pre-set TRVs; the second group encompasses buildings that were already equipped with TRVs and then a hydraulic balancing of the heating system was performed by means of a pre-set; finally, the third group of buildings considers the simultaneous installation of TRVs and hydraulic balancing of the heating system using pre-set TRVs. The energy savings ranged between 7.1% and 23.3%, depending on the range of modernization activities using TRVs with or without hydraulic balance. The payback time was less than 2.5 heating seasons in all cases.