Steam reforming reaction heat effects were implemented in CFD simulations of different packed tube models of 1-hole and 4-hole cylinders. A computationally less expensive 120° wall segment approach was utilized for the simulations in this study. Heat effects of the reactions were introduced by heat generation/consumption terms in the catalyst particles considering suitable reaction kinetics proposed in the literature. Due to strong diffusion limitations the activity of the catalyst particles is confined to a thin layer at the particle surface. Therefore, the energetic effects of the reactions were restricted to the outer 5% of the particle dimension by a user-defined code. The selection of the correct active region was verified for both the particle external and internal–hole surfaces. Simulation results of the reaction heat effects were qualitatively and quantitatively compared to cold flow cases where there were no heat effects but only tube wall heat transfer. Due to the endothermic nature of the reactions, relatively lower temperature fields were observed when the heat effects were introduced, where the positions of the solid particles play an important role. The implications of introducing the detailed reaction heat effects were emphasized in the development of suitable packed tube models.