This study focuses on the modeling and design of a district heating system for a residential complex inspired by the Maskan Mehr housing project, where heating is currently provided by fossil fuels (natural gas). The complex comprises six blocks, each with nine residential units of 65, 75, and 85 m². An independent boiler system was modeled and designed to estimate both thermal and electrical energy demand. The research also explores the integration of solar energy with natural gas as a hybrid supply source for the district heating system. For each scenario, key performance indicators—including carbon dioxide emissions, total energy consumption, and associated costs—were assessed. Simulations were carried out using TRNSYS, DesignBuilder, and Valentin TSOL software. The results show that annual space heating energy consumption is 51 kWh/m²·year for the independent boiler system, compared to 47 kWh/m²·year for the district heating system. Carbon dioxide emissions were calculated at 92,425 kg for the boiler system and 62,731 kg for the district heating system, highlighting the environmental benefits of district heating when supplemented with solar energy.