A method for modeling and monitoring the amount of fouling in a heat exchanger (E) is developed with the present invention. Said method comprises the steps of assigning a temperature difference for the inlet and outlet temperatures for the fluids (100); calculating an iterative outlet temperature for the fluids (101); determining an expected outlet temperature for the fluids (102); finding average temperatures for the fluids (103); calculating an iterative clean heat transfer coefficient for the heat exchanger (E) (104); calculating a logarithmic mean temperature difference (105); updating the iterative outlet temperature (106); comparing the iterative temperatures to the expected temperatures (107); returning to the step of determining an expected outlet temperature for the fluids (102) if the temperature difference for at least one fluid is above a predefined value; otherwise, finding instantaneous values for the heat exchanger (E) (108) and calculating the amount of fouling in the heat exchanger (E) (109).
