A heat transfer model of a semi-industrial furnace has been build, using a 3D FEM model in order to analyze the crystallization phase of a multi-crystalline square ingot. In the modeling of the solidification process heat transfer phenomena, such as radiation and conduction in the furnace have been taken into account. Results from crystallization experiments are used for the calibration and validation of the model. Subsequently, the model was used to test different insulating materials and analyze their effect on temperature gradients in the ingot, shape of the solid-liquid interface and the overall crystallization time. (C) 2012 Elsevier B.V. All rights reserved.