In the study presented a new efficient thermal model has been implemented to the coil in oil-immersed transformer windings. In order to show thermal model efficiency eight-disc-coil has been modeled. The governing equations of the model developed were solved by a numerical-analytical method to obtain temperature distribution. The heat transfer coefficients for the convection processes are evaluated for an accurate prediction of the hot spot temperature location. The governing equations were solved in both radial and axial directions. All the evaluations used the model developed are verified by using Finite element-based packet program ANSYS. Both results obtained are in good enough agreement with open literature.