The knowledge of ideal gas properties of refrigerant molecules is crucial for the design and optimization of refrigerant production processes and the simulation of energetic systems. In this work, the ideal gas properties of chlorinated and fluorinated hydrocarbons have been predicted by using different methods based on quantum calculations. Enthalpies of formation have been predicted by using semi-empirical methods such as PM3, PM6 and PM7, as well as the procedure of Osmont et al. [Combustion and Flame, 151 (2007) 262–273]. We obtain a good agreement between the enthalpies reported in databases and the predictions from ab initio calculations, for most refrigerant molecules. The ideal gas heat capacities of refrigerants can be accurately predicted by using MP2-DGTZVP and B3LYP/6-31G(d,p) ab initio calculations, and rescaling the vibrational temperatures by a factor of about 0.98. The method is extended to hydrofluoroolefins (HFO) and excellent predictions of heat capacities are obtained.