Consideration of the scheme of flows of combustion products in furnaces and flow chambers of combus-tion within the framework of the heat transfer paradigm made it possible to determine the ratio of the genera-lized mechanisms of heat transfer – convection and radiation. The transition from uniform distribution of gas flow velocity to uneven distribution in furnaces with a geometrically peculiar fence has been implemented. This made it possible to take into account the use of recirculation gases, dual-light shades, changes in the shape and size of the cross-section of the furnace, and installation of shade surfaces in a furnace. The condi-tions for the correctness of the mathematical model are considered, and the eigenvalues of the boundary value problem under conditions of an asymmetric temperature field and the function of the gas temperature changing along the height of the furnace are obtained. A comparative analysis of the nature of the change in gas temperature with height according to the proposed model with the calculation for a steam boiler with a capacity of 950 t/h according to the standard method showed a satisfactory agreement of the calculated data with an accuracy of +4.87 %.