Numerical results obtained with the finite difference method are presented on natural convection in a porous cylinder with internal heating and side−wall cooling, for aspect ratio H (height vs. radius) 4, 8, and Rayleigh number ranging 1−10⁵, with effects of non-uniform heat generation and different top boundary conditions taken into consideration. Natural convection generally has an effect of cooling down the temperature field, thus resulting in a maximum local temperature lower than that calculated by the pure conduction model, which is considered to be conservative in security assessment. In the case of uniform heating and an adiabatic top end, however, the maximum, occurring at the center of the top boundary as a result of heating by upward−flow impinging on the point, could exceed that calculated by the conduction model. Cooling on the top boundary can dramatically reduce the maximum local heat flux on the side wall, thus preventing possible damages in engineering problems.