The development of numerical analysis may be slowed if detailed descriptions of the processes in thermal equipment are included in the mathematical models. Therefore, it is of interest to develop methods that simplify the calculations without significant loss of accuracy. In high-temperature chambers, radiation is the main heat-transfer process; it is also very difficult to describe in mathematical terms. Smoky gases emit and absorb heat within spectral bands that combine several lines. The parameters, shape, and interaction of the lines depend on the temperature, pressure, and composition of the gases. Models of relatively simple bands (selective‐gray bands) and fairly complex bands were described in [1‐4]. All the models require laborious spectral calculations; as a rule, the models are experimentally verified only in terms of calculations for the radiation of isothermal gas. In engineering calculations, a simple model of a gray gas is most often employed; it yields acceptable accuracy only with relatively small temperature differences in the chambers. In the present work, we propose a model of the integral characteristics of selective radiation of a nonisothermal gas bounded by gray walls. In the model, the heat fluxes in the chambers are represented as the sum (superposition) of heat fluxes due to individual heat sources (individual surfaces and zones of the gas). A description of the heat transfer in the chamber may be obtained in this form on the assumption that the successive radiation fluxes from the surface and volume zones of the gas in the nonisothermal volume are nonzero. The radiation fluxes are characterized in terms of their sources. It is then possible to use existing experimental or experimentally verified formulas taking account of the selectivity of the radiation. From these formulas, the heat transfer of each of the interacting pairs of objects may be calculated: for example, a wall and a gas layer, two layers of gas, or two walls. The model assumes that the thermal-radiation fluxes are additive; this is the case in the usual conditions for heating systems—at near-atmospheric pressure, with steady or very slowly varying temperature fields, in the absence of powerful radiation fluxes or powerful magnetic and electric fields, and in the absence of very large temperature gradients. On the basis of this physical model, methods of calculating the radiant heat transfer in chambers may be developed. In a number of cases, the formulas are analogous to known solutions of the heat-transfer problems of gray bodies in chambers. The radiant heat transfer in a plane nonisothermal layer of gas bounded by walls 1 and 2 is most clearly described by the multiple-reflection method [5]. The temperature distributions are specified or are determined in each step of the iterative heat-transfer calculation. The heat flux incident on wall 2 as a result of the intrinsic radiation of wall 1 is