One of the pitfalls of engineering education is to lose the physical insight of the problem while tackling the mathematical part. Forced convection heat transfer (the Graetz-Nusselt problem) certainly falls into this category. The equation of energy together with the equation of motion leads to a partial differential equation subject to various boundary conditions. Since heat transfer to and/or from the fluids flowing inside circular pipes has many industrial applications, such as evaporators and heat exchangers, heat transfer courses cover this topic extensively. When the heat flux at the wall is constant, the solution is rather straightforward. However, when the wall temperature is constant, the solution becomes complicated and the end result is obtained using an iterative procedure. Thus, many textbooks, as well as the instructors teaching the course, usually omit this section by simply stating that the end result yields the Nusselt number to be equal to 3.66. The purpose of this paper is to show students how to get this result without going into too much mathematical detail.