Environmental impact re-evaluation of coal-fired district heating systems from the marginal life cycle perspective

District heating (DH) systems based on waste heat recovery from coal-fired power plants have been widely deployed worldwide. Nevertheless, a persistent academic and policy debate persists regarding the necessity to transition toward other low-carbon alternatives due to DH's fossil energy depletion and carbon lock-in effects. Life cycle assessment (LCA) has been extensively applied to evaluate the environmental impacts of DH systems, while the traditional environmental impact allocation methods often lead to inaccuracies in such complex multi-functional systems. This study introduces an improved allocation method based on marginal perspective to deliver a more accurate and dynamic LCA of DH based on coal-fired power plants in northern China. The results reveal that DH systems cause health damage of 3.17 × 10 −7 DALYs/kWh and greenhouse gas emissions of 276 g CO 2 eq/kWh, which are overestimated by more than 80% within conventional partitioning methods. The comparisons reveal that DH systems based on waste heat recovery from non-decommissioned large coal-fired units retain an advantage over natural gas or heat pump alternatives. The ongoing phase-out of coal-fired power plants and the expansion of renewable energy could diminish the environmental benefits of by-product substitution, potentially making DH less competitive. This study proposes to fully utilize the waste heat resources from coal-fired units during their pre-retirement phase, and prudently determine the optimal timing for transitioning to heat pump heating. The findings provide valuable insights for decarbonizing domestic heating and supporting the sustainable development of coal-fired power plants. • Environmental consequence of district heating is revealed by life cycle assessment. • The CO 2 emission factor for district heating is re-calculated as 276 g CO 2 eq/kWh. • Substitution is more reliable than partitioning to evaluate the cogeneration plants. • Conditions for replacing coal-based district heating with heat pumps are not mature. • Waste heat from not-yet-decommissioned coal-fired plants should be fully utilized.