The performance of the discrete transfer and of the six-flux radiation models is assessed in a swirling natural diffusion flame confined in an axisymmetric furnace. The predictions are evaluated as part of a complete prediction procedure involving the modeling of the simultaneously occurring flow, combustion, convection and radiation phenomena. Computational results with and without radiation effects are compared with experimental data and the two radiation models are evaluated in terms of computational efficiency, ease of application and predictive accuracy. The results have demonstrated that the effect of thermal radiation is important even in light flames, and that the six-flus model can be applied in industrial gas furnaces with relative ease, yielding accurate predictions. (C) 2000 Elsevier Science Ltd. All rights reserved.