Many design methods for the retrofit of heat-exchanger networks have been proposed during the last 3 decades. Conventional retrofit methods use additional area to accommodate the increasing heat duty. However, the implementation of additional area may prove difficult because of topology, safety, and downtime constraints. This problem can be mitigated through the use of heat-transfer enhancement. This Article investigates the influence of heat-transfer enhancement on fouling in heat-exchanger networks. A novel design approach is used to solve heat exchanger network retrofit problems on the basis of heat transfer enhancement by considering fouling. Simulated annealing is used to optimize the retrofit problem under fouling conditions. The results show that heat transfer enhancement is a very attractive option for retrofitting when fouling is considered. The consideration of fouling in heat transfer enhancement has the potential to make a significant impact on retrofit design and to make the design more cost-effective than conventional design approaches.