Building energy consumption constitutes a major source of carbon emissions. The heating energy consumption of rural buildings in the Hot Summer and Cold Winter (HSCW) zone has increased 575-fold over the past 15 years due to many notable contrasts with northern cities in China. Thus, this research investigated the Solar-Air Source Heat Pump (SASHP) system to address the heating demands of rural residences in the HSCW zone. A model of the typical rural building in Hangzhou city was developed firstly, revealing an average heating load of 3.38 kW and a peak load of 5.9 kW. Then, the SASHP system was designed and subsequently optimized to minimize the annualized cost. The optimization yielded key parameters: a solar collector area of 15 m² with a 41° tilt angle, a water tank of 0.3m3 volume and an air source heat pump with a rated power of 10.125 kW. Concretely, the optimized system achieved a coefficient of performance of 3.67 for the overall system, while maintaining the indoor thermal comfort within ISO 7730 Category II standards. Compared to the designed system, the optimized configuration reduced the initial investment and the annual operating costs by 40.75% and 33.09% respectively. On the whole, the optimization significantly enhances the economic viability of SASHP systems, providing a sustainable pathway facilitating carbon neutrality in China.