Wastewater heat recovery applications are becoming widespread in energy saving applications. A sustainable and low emissions operation in air conditioning and heating processes is achieved by harvesting the otherwise wasted energy in wastewater through specially designed heat exchangers, lying at the core of heat pumps. This combined system is called wastewater source heat pump. In this study, a review of wastewater heat exchangers in wastewater source heat pump applications is presented, and wastewater heat exchangers are classified in detail based on multiple features, including utilization and construction methodology. Also, the potential of wastewater, types of wastewater source heat pumps, and their applications are briefly discussed. (C) 2015 Elsevier B.V. All rights reserved.