Different approaches for the approximate prediction of heat transfer rates between gas fluidized beds and immersed surfaces are analyzed in this work. They concern the interstitial gas and radiant contributions that have been frequently accounted for by adding approximate terms to the particle convective component which is usually the principal component. A generalized heterogeneous model considering simultaneously the three mechanisms and their interactions is presented and used to assess the validity of some previous approximations. This analysis is carried out by scanning practical ranges of the main decision variables : operating pressure, temperature and particle size.