In the UK, natural gas dominates the provision of heating in buildings. In Sweden, oil heating has been largely replaced by district heating and heat pumps. The origins and outcomes of path dependence and lock-in in heat system evolution can be country specific. Here, we compare case studies of heat transitions in the UK and Sweden, addressing the question: can path dependency help to understand why these countries have followed different paths in terms of change to their heating infrastructure? In both countries the development of heating infrastructures can be understood as path dependent processes, entailing increasing returns to adoption as fuel sources, infrastructures and end use technologies coevolve such that the overall performance of the system increases. The challenge for policymakers seeking to achieve carbon targets is to consider how to create the conditions to encourage increasing returns to adoption of low carbon heating solutions.