The ability to predict and control morphology of castings through solidification simulation depends upon the modeling of heat transfer at the metal/mold interface. Since solidification is a dynamic process governed by the rate at which heat transfer takes place at the metal/mold interface, the thermal boundary condition applied at the metal mold interface becomes critical. In this article, two types of boundary conditions i.e. (a) single heat flux and (b) an optimal multiple heat flux configuration were used for 2-dimensional solidification simulation of thin Al-11.8 pct. Si plates cast in gray iron molds. The time-temperature curves computed by both the single and multiple heat flux boundary conditions reveal close match with the measured and computed temperatures at the centre of the castings. However, the thermal fields in the casting and the die reveal one-dimensional nature of the heat flow throughout the interface for single heat flux boundary. For multiple heat flux inputs, the two dimensional heat flow is more pronounced representing temperature non uniformity with space and time as the solidification progresses.