The energy market development in the last decade has been influenced by several driving factors. To meet the strict customers’ requirements (related to low emissions, flexibility and high performances), operate gas turbine plants safely over a variety of off-design operating conditions has been fundamental. Accordingly, accurate evaluation of running clearances in stationary and transient conditions plays a significant role. On the other hand, the study of heat transfer in turbo-machinery is a fundamental activity to study the implications of off-design operating on components’ lifing. Focus of the paper is the analysis of variations of components’ wall temperature and clearances due to the fluctuation of thermal loads acting on gas turbines components during operation. The study is divided into two main sections: heat transfer analysis allows evaluating thermal loads and then a FEM analysis is performed in order to calculate the radial and axial clearances between rotor components and casing. Thermal loads are obtained by a computational method based on heat transfer correlations. Parametric curves have been developed to calculate variations of thermal loads in transient conditions from steady-state data obtained by the correlative computational tool. The two procedures for heat transfer analysis and evaluation of clearances have been validated against experimental data in several operating conditions. In particular, relative and absolute movements of rotor and turbine casing have been measured by means of proxy-meter probes located into the turbine bearing casing.