The heating sector is a major source of emissions in the Baltic Sea region and its decarbonization is crucial. To encourage the transition to more sustainable heating solutions, the EU requires municipalities with more than 45,000 inhabitants to develop local heat plans. The PlanHeat project aims to assist local authorities in this endeavour, by creating a transnational manual on local heat planning. Involving municipalities and experts from seven countries, it will provide guidance on data use, technologies, staff training, stakeholder involvement, and financing. In the final project phase, “Ambassador Cities”, that are involved in project activities from the start, will help to promote and distribute the manual region-wide.