A comparison between energy performance, simulated by means of the EnergyPlus building simulation program, of two air systems (all air and fan coil) and radiant heating and cooling floors/ceilings is developed in this work for various European climates (Milan, Frankfurt, London, Madrid, Athens, Helsinki, and Moscow) and carried out on a reference building selected from among U.S. Department of Energy commercial building new construction benchmarks. The comparison is focused on the analysis of energy sources and CO2 emissions at equivalent thermal comfort quality levels in the various cases. The adoption of a radiant system, and of an appropriate primary energy system, always results in a reduction of energy sources exploited, of costs for e...