A method based on geometric reasoning techniques is presented to predict hot spots and use of geometric parameters of a casting to obtain effective interface boundary conditions. The proposed method combines Chvorinov's rule and Heuvers' circle method with the medial axis transformation technique to develop an elegant optimisation technique for the optimal feeding design of castings. The results are validated using a FE based solidification analysis. It has been shown that the method has the ability to constrain heat transfer coefficient values to yield more realistic predictions for foundry practices. The proposed method has a considerable potential to reduce the number of FE simulations that are otherwise needed to achieve an optimal thermal design.