Reboilers are essential for the proper work of distillation and stripping columns. Hereby the intensity of axial mixing along the reboiler (Peclet number) is used for the reboiler separation efficiency modeling and estimation for binary systems. Two fully worked examples show that the separation (Murphree) efficiency varies significantly depending on the adopted reboiler flow model. Murphree efficiency ranges between 1.40 and 0.663 in example 1, and between 1.962 and 1 in example 2. The general conclusion is that the reboiler performance must be considered carefully in the case of design of the new plants,as well as in the case of "brown field" projects.