A comprehensive computational model for the design of methane catalytic partial oxidation monolith reactors for hydrogen production has been developed and tested with respect to available experimental data. Allowing a simplified description of the heat release mechanism associated with the reforming process, the model represents a useful tool to address performances and durability issues in the design process of full scale catalytic reformers. The characteristic temperature peak along the catalyst channels, which is experimentally observed as a result of the competitive action of fuel complete oxidation and steam reforming is, in fact, a fundamental parameter to be controlled during the design process and is a complex function of catalyst formulation, mixture composition, and actual operating conditions. To address this issue in the present paper the heat release law mechanism has been studied with a new approach named heat release curves model (HRCM), which decouples the thermofluid dynamic analysis of real geometries from the modeling of heterogeneous chemistry. The model uses heat release curves extrapolated from detailed heterogeneous chemistry calculation or experimental measurements as the basis of a simplified, although still predictive, evaluation of the heat released, which allows a substantial reduction in computational costs. Validation of HRCM model (including heat release profiles approximation) with respect to more detailed simulations and available experimental data shows very good predictive capabilities with a maximum error lower than the 4% over a wide number of analyzed cases (accounting for several O/C ratios, inlet velocities, channel dimensions, and mean temperatures). Although presented for natural gas reforming the present model may be easily extended to different fuels.