This study assesses the technical potential for wastewater heat recovery in Sofia and its contribution to domestic hot water supply and greenhouse gas reduction. Heat extraction locations were identified using temperature and flow data from the sewer network and the municipal wastewater treatment plant (WWTP) Kubratovo. Temperature thresholds were defined to ensure stable biological treatment ( ≥ 10°C influent) and environmental protection ( ≥ 5°C effluent). Four scenarios were analyzed, conside