The aim of this work is to elaborate a method of identification of the influence of fouling on the heat recovery in a heat exchanger network (HEN). The method is based on mathematical models enabling the interpretation of industrial measurements of operating parameters of the HEN. Details of the models are developed for shell and tube heat exchangers. The crucial assumption is that measurements of the mass flowrate and inlet and outlet temperature, and chemical composition are available for each process stream, this making it possible to evaluate fouling-induced reduction in the recovered energy flow. Using the proposed identification method and an industrial data base acquired in a typical crude distillation unit, the mathematical models are thoroughly tested. The developed approach allows long-term monitoring of changes in the condition of the HEN and assisting plant operator decisions aimed at maximizing heat recovery over the period of plant operation. A case study and an example of optimal scheduling of cleaning interventions on the individual exchangers are presented. (c) 2012 Elsevier Ltd. All rights reserved.