## 4 Conclusions  
This review study aims to provide a comprehensive overview of current methodologies and technical considerations for reducing return temperatures in DH systems. Maintaining low return temperatures is increasingly vital for enhancing overall system efficiency. However, return temperature is not a parameter that can be directly controlled; it is influenced indirectly through various system parameters considered during the design, commissioning, operation, and control phases. This review highlights key aspects that impact return temperature, including technical considerations within the DH network, cascading applications, innovative concepts, and control strategies. The section on heat sources examines the impact of return temperature on heat generation efficiency. Additionally, non-technical factors, such as pricing strategies and the delineation of ownership boundaries, are also addressed. System-level optimization, integrating both technical and non-technical factors, constitutes the final observation in this review. Several general conclusions emerge from this review, highlighting areas that have not yet been extensively explored. Hydraulic imbalance across the network significantly contributes to elevated supply and return temperatures in DH systems. Bypass flows, which often exacerbate high return temperatures, are not universally redundant. Cascading provides a notable advantage by enhancing the utilization of available heat and reducing the overall return temperature. Cascaded networks are particularly effective in systems operating under varied temperature schemes, optimizing heat utilization and substantially lowering return temperatures. The variable-flow control strategy, which adjusts flow using variable-speed pumps and decentralized self-regulating flow control valves at end-user sites, offers a more effective alternative to constant-flow systems. Similarly, a variable supply temperature system based on weather compensation generally performs better than a constant temperature scheme, though proper commissioning of the weather compensation curve is essential for site-specific optimization. The interplay between return temperature and reduced flow rates benefits various heat sources, including cogeneration units, heat-only boilers, heat pumps, solar collectors, and industrial excess heat recovery systems. System-level optimization is crucial, involving site-specific temperature adjustments and annual analyses to account for lifecycle costs and environmental impacts. Effective implementation strategies should focus on incentive tariffs to motivate end-users to reduce return temperatures or develop pricing structures based on the internal energy of the supplied medium. Additionally, substation maintenance must include annual inspections, either mandated by legislation or conducted by the DH company. Pressure-independent thermostatic radiator valves can help maintain hydraulic balance while mitigating thermal discomfort and high return temperatures. Demand-driven pumps, installed decentrally at end-user substations, present a viable alternative to traditional DH systems. Furthermore, smart heat metering systems facilitate ongoing monitoring of end-user substations and should be given due consideration. This review highlights the necessity of a holistic approach to optimizing DH efficiency, emphasizing the interdependence of network design, operational strategies, control mechanisms, heat source utilization, and consumer engagement. Achieving sustained improvements in return temperature reduction requires a system-level perspective where hydraulic balancing is prioritized, bypass applications are minimized, and cascading is effectively implemented when temperature conditions allow. The reciprocal relationship between network operation and control strategies further underscores the importance of integrated planning, ensuring that system-wide adaptations enhance rather than constrain efficiency.