The efficiency of heating systems is increasingly important because of the increasing need to save energy and protect the environment. This paper presents an innovative technique for modeling multi-zone hydronic heating systems in buildings in an easier and more user friendly manner. An original approach is described in which the thermal and hydronic systems are solved simultaneously by simulating the dynamic behavior of pipe water flow rates, water temperatures, and room air temperatures. The simulation uses mathematical models that apply a Newton-Raphson method (NRM) developed in Matlab(C) and Simulink(C) environments. A user friendly graphical user interface (GUI) enables the designer to analyze any multi-zone hydronic heating system from the point of view of improving its efficiency. A laboratory heating system was used to validate this modeling technique. A series of trials were conducted in a multi-zone laboratory heating system located within the R&D division of a leading Italian boiler manufacturer, and the results presented in this paper validate the model. (C) 2009 Elsevier B.V. All rights reserved.