Condensing boilers allow better performances when return temperatures from the plant are lower and above all when these temperatures are below the dew temperature of the smoke. That is the reason why many believe that condensing boiler is not suitable for the traditional heating plant terminals: the radiators. Instead the classic control system with weather compensation curve produces relatively low temperatures and an appreciable condensing operation during March, April, October and November. Moreover. condensing boilers allow a better performance than traditional boiler even when they do not perform condensing operation. However for the optimum exploitation of condensing boilers in a radiator plant, variable-flow-rate plants should be selected that permit every outside condition to maintain a high difference between delivery and return temperature. This control selection, which is fully consistent with the use of thermostatic valves, needs variable-flow-rate pumps and, if possible, with proportional head. (C) 2011 Elsevier B.V. All rights reserved.