This report compares two primary pathways for decarbonizing building heating in Ontario, Canada: widespread electrification using heat pumps and extensive deployment of thermal networks (district energy). Through comprehensive data analysis, literature review, and expert consultation, the study quantifies the technical, economic, and social implications of each pathway. Findings reveal that electrification, especially with air-source heat pumps, would require a massive and costly expansion of the electricity system, with significant challenges during winter peaks. In contrast, thermal networks could efficiently serve up to 70% of Ontario’s buildings at a much lower societal cost, leveraging waste heat, combined heat and power, and large-scale thermal storage. The report recommends a hybrid approach—thermal networks in dense areas and ground-source heat pumps in rural zones—supported by municipal planning and sector coupling. It concludes that strategic integration of these solutions is essential to achieving net-zero emissions by 2050.