The question of how to optimally decarbonise the buildings sector – especially heating – remains a source of fierce debate. A large amount of uncertainty remains around how to strike the optimal balance between heat demand reduction and heat supply decarbonisation. This paper sheds light on the complex search for the optimal balance between reducing heat demand and decarbonising heat supply. Drawing on economic theory and cost-benefit analysis, the paper proposes an analytical framework that structures and organises the many complex and intertwining parameters to consider when determining this optimal balance. We conclude that increased clarity about the goal, scope of, and method for optimisation efforts are the foundations of a more informed and considered approach when it comes to decarbonising heating. The paper also provides insights for policy makers faced with the challenge of designing policies and regulations in this area.