Fouling of heat exchangers is a major problem on naval surface ships and submarines as well as commercial vessels and land-based cooling systems. Fouling of heat exchangers causes the thermohydraulic performance of heat transfer equipment to decrease with time. The heat exchanger must be cleaned as the thermal hydraulic performance decreases to a minimum acceptable level. The decision regarding periodic cleaning of a heat exchanger is generally based on the thermoeconomic performance of the process. In this article, freshwater (as coolant) and seawater temperatures and pressures through a seawater cooled shell and tube heat exchanger during 2500 operating hours have been measured, and total fouling resistances have been calculated. There is a good agreement between the model and the experimental fouling resistances. The dimensionless cost model and its variation with the dimensionless time are examined by considering the various cost elements for the heat exchanger. An optimum cleaning cycle for the case heat exchanger has been offered to minimize the total operating cost. (C) 2013 Elsevier Ltd. All rights reserved.