The erosion of hearth refractories typically governs the asset life of a blast furnace. Since operating conditions within the hearth make it practically impossible for direct measurement and visualisation, physical and mathematical models play an important role in understanding and assessing the cause-effect phenomena between the liquid iron, coke bed and refractories. A numerical model has been developed to predict the iron flow and temperature distribution within the packed bed and refractories. A number of case studies have been investigated for Port Kembla's No. 5 blast furnace, which is entering the 15th year of its current campaign. These case studies considered the effects of coke free layers (floating/sitting deadman), hearth deposits, coke bed fouling and localised refractory erosion. The refractory temperature distributions predicted by the model compare well with the blast furnace thermocouple measurements and as a result, the model has become a valuable predictive tool for hearth design and control.