This paper proposes a dynamic analysis of fouling of a heat exchanger. The used criteria is mean thermal power exchanged over time. The proposed results are relative to cocurrent configuration and tubular geometry of the heat exchanger, but other cases have been explored (countercurrent, plane geometry). An optimum time is determined, sensitivity analysis of the corresponding value to three cases of flow regimes (constant mass flow rate, constant flow velocity and constant pumping power) and various kinetics of fouling has been performed. The time of stop of the installation for cleaning is the main parameter. All the results are proposed in nondimensional form. This paper was presented at the ECOS’98 Conference in Nancy, June 8-10, 1998