The presence of biofouling layers on heat transfer surfaces can reduce heat transfer efficiency markedly. A new method for inhibiting biofouling growth and promoting rapid online cleaning for heat exchangers recovering thermal energy from treated sewage streams based on a temporary coating is reported. A paraffin wax coating is cast in place without needing to disassemble the device, while the low roughness and hydrophobicity of the coating inhibits bacterial growth. The coating and any attached biofouling can be removed by raising the surface temperature above the wax melting point. The effectiveness of this online cleaning and inhibition strategy was investigated using a simple laboratory test channel, representing a plate heat exchanger, and a process stream simulating treated sewage. The thermal resistance was monitored and showed that the reduction in biofouling thermal resistance eventually outweighed the additional thermal resistance resulting from the coating. A techno-economic analysis is presented to quantify the advantages of the paraffin coating method in terms of energy saving and cost reduction.