A model for evaluating radiative heat fluxes in tubular heat exchangers is proposed. In this model it is assumed that individual tubes of the bundle are surrounded by a gaseous layer The actual geometry was approximated by an equivalent cylindrical gaseous medium to simplify the problem. A mathematical procedure was developed based on this and other assumptions to evaluate the gas-radiation coefficient. The procedure can be incorporated in any arbitrary program for thermal and hydraulic calculation of a tubular heat exchanger. The applicability of this method for determination of the radiative heat transfer coefficient (h(R)) is demonstrated on the exchanger-type primary reformer and the variation of h(R) under different geometric and operating conditions is studied using the procedure developed.