Fouling affects heat exchangers’ performance leading to additional utility requirements and economic penalties. Performance monitoring is required to ensure that exchangers operate within allowable limits. Conventional techniques use overall heat transfer rate to monitor thermal performance. These techniques fail when the heat transfer rate remains constant, which is the case anytime a heat exchanger has feedback control on temperature. In this paper, we propose an approach to monitor fouling in heat exchangers that have closed-loop control. Our approach is based on excess pressure drop and thermal load. A monitoring chart is also proposed based on combined hydraulic and thermal performance indicators. The proposed monitoring charts are demonstrated on two case studies – a cooler with a utility on the tube-side and a heater with the utility on the shell-side. The results show that even when setpoints and flowrates change due to process requirements, the proposed approach can effectively monitor fouling and identify if the operation is within allowable performance bounds. The results can be used to schedule the cleaning of the exchangers at an appropriate time so as to avoid excessive economic losses. © 2022 Institution of Chemical Engineers