In order to effectively design the complex duct systems in a refrigerator which consists of evaporator fan, and various shapes of duct, a computer-aided design program for refrigerator duct systems is developed by using both the thermal network and extended T-method. The technique of this program allows rapid and accurate comparison of the relative performance of different designs and suggests different design improvements. The developed program is verified by comparison of its calculated flow properties with those from CFD analysis for the same model. There are some discrepancies between these results, since the developed program has a one and two-dimensional approach, while the CFD analysis used is a full three-dimensional approach. However comparison results show a qualitatively good agreement.