Heat has become a central concern for cities everywhere, but heat governance has historically lagged behind other climate change hazards. This study examines 175 municipal plans from the 50 most populous cities in the United States to understand which aspects of urban heat are included or not in city plans and what factors explain inclusion. We find that a majority of plans mention heat, but few include strategies to address it and even fewer cite sources of information. The term ‘extreme heat event’ (EHE) is significantly more likely to be paired with institutional actions as a part of hazard planning, while ‘urban heat island’ (UHI) is more likely to be paired with green and grey infrastructure interventions as a part of general planning. Disparity and thermal comfort framings are not significantly related to any solutions and are used least. Plan type, followed by environmental networks (e.g. C40, Urban Sustainability Directors Network, Rockefeller 100 Resilient Cities), explain variation in plan content; social and environmental context do not. Findings point to the emergence of two independent heat governance systems, EHE and UHI, and several gaps in heat planning: integration, specificity, solutions, disparity, economy, and thermal comfort.