The paper develops a mathematical model of the combined processes of heat conduction, convective and radiant heat transfer in the working space of an industrial gas furnace. Analytical expressions for the heat flux components are derived. Two-dimensional temperature field simulation is carried out using the finite difference method. Model verification is performed by comparing calculated and experimental data: the root-mean-square deviation did not exceed 14°C (1.3%). A sensitivity analysis of the model with respect to the emissivity ε and convective heat transfer coefficient α is conducted.