Thermal energy storage devices are vital for reducing the inconsistency between energy supply and demand as well as for enhancing the performance of solar thermal systems. The present study investigates the melting process in metallic honeycombed heat exchangers filled with n-octadacane as phase change material (PCM). Further, a parametric study is conducted for four different honeycomb cell sizes, fin thicknesses, and angles of inclinations of the computational domain. The findings are described in the form of heated surface average temperature variation, melt fraction of the PCM, and thermal energy stored. Results show that the honeycomb fin structure considerably improves the heat transfer in the PCM. Further, it was observed that the honeycomb cell size and fin thickness greatly influence the variation of the average front surface temperature, melt fraction, and energy storage rate, whereas the inclination angle doesn’t have a significant effect when cell size is less than 0.01 m. From the study, it was also observed that when the computational domain is horizontal without honeycomb cells, the pure conduction in the PCM results in much higher front surface temperature, which is greatly reduced in presence of the honeycomb cells.