Net-zero district heating systems are considered a feasible heating alternative to replace individual natural gas boilers to mitigate emissions in European cities. However, achieving carbon-neutral cities in Europe is a complex affair due to interdependencies in energy transitions. Energy transitions are discussed as products of interdependencies between socio-technical elements within each context, including but not limited to institutions, society, culture, markets, policies, regulations, and technological disruptions/changes. These interdependencies have the potential to transcend beyond the boundaries of technologies, sectors, markets, policies, cities, and even countries which may result in feedback effects. The presence of feedback effects implies co-evolution: policy-making shapes energy system developments which, in turn, influences policy-making through a range of feedback effects. The objective of this study is to increase knowledge on the implications of feedback effects in energy systems and transition policies by highlighting how they can lead to unexpected systemic consequences, thereby causing inertia or acceleration during the switch out of individual natural gas boilers towards net-zero district heating systems. Understanding the root causes and mechanisms behind district heating transitions could support European policymakers in developing policies that can stimulate the transition toward carbon-neutral cities. Our results implicate that energy transition governance seldom consists of “simple” fixes as often claimed by popular policymakers or influential actors because each decision impacts the whole system. Different policy sub-goals are indispensable for achieving carbon-neutral cities but they are often indirectly in conflict with each other due to feedback effects. Unless feedback effects in transitions are acknowledged by policymakers, they could work against carbon-neutrality targets due to wrong assumptions and prioritizations of inconsistent policy sub-goals. Therefore, it is essential for policymakers to recognize and comprehend how feedback effects between energy systems and policies are formed and operate.

District heating systems are considered a feasible heating alternative to replace natural gas to mitigate emissions in cities. However, urban transitions are very complex because energy systems often operate in densely populated areas, which gives rise to all kinds of interdependencies in cities. These interdependencies can result in unintended consequences which can indirectly help or hinder urban energy transitions. Understanding these influences the transition to climate neutrality. This research investigates the lessons learned from a project conducted in Rotterdam: a high-density city in the Netherlands which is expanding its district heating systems. We use qualitative system dynamics models to explore the underlying complexity and to recognize indirect consequences of policies. Our results cover both technologically oriented and policy-oriented insights, contributing to the literature on transition governance in cities. On the one hand, the national and urban strategies in the Netherlands activate mechanisms that support cities with district heating systems such as Rotterdam. On the other hand, the same strategies could also lead to a potential rivalry between energy efficiency and energy security, which are both crucial goals in urban transition governance. Participative modeling provides policy-makers with an analytical tool to detect systemic dependencies which can be used to identify synergies and barriers among different energy policy objectives. This helps avoiding potential unintended consequences including the use of carbon-heavy systems and displacing investments from energy efficiency and renewable heating systems.