Radiative heat transfer is of major importance in many large-scale fires. Therefore, a new extinction coefficient algorithm has been developed for the Consolidated Fire Growth and Smoke Transport (CFAST) zone model. The new algorithm estimates extinction coefficient as a function of temperature and absorber concentrations. A developmental version of CFAST (2.2.1) was used, with and without the new algorithm, to simulate a large-scale, shipboard fire. For the fire compartment and the deck (floor) directly above, predictions from both models compared well with experimental results. The improved radiation model gave much better results for the adjacent compartment. Neither model compared well with the experimental results for the remainder of the compartments, suggesting that there is still room for improvement to CFAST.