Despite their high energy consumption, rural residential houses in the hot summer and cold winter (HSCW) zone still have a generally poor indoor thermal environment. The objective of this study was to understand the current status of the indoor thermal environment for rural residential houses in the HSCW zone and analyze its cause in order to develop some strategies for improvement through passive design of the building envelope. Face-to-face questionnaires and interviews, air-tightness testing, and temperature and humidity monitoring were conducted to understand the building envelope, energy consumption, and indoor thermal environment. Then, some passive design strategies were simulated, including the application of functional interior materials such as hygroscopic and phase change materials. An overall passive design for the building envelope can increase the room temperature by 3.6 °C, reduce the indoor relative humidity by 12% in the winter, and reduce the room temperature by 4.4 °C in the summer. In addition, the annual energy-saving rate can reach ~35%.

Understanding the thermal performance of the residential envelope is important for optimizing the indoor thermal environment. In this study, the indoor thermal environment and thermal performance of rural residences housing the elderly was determined through field measurements in Qiqihar in 2017 and 2019. The results revealed that the living room temperatures in more than 50% of homes were below the thermal neutral temperature for the elderly (17.32 °C). Moreover, the indoor thermal environment changed significantly during the day, with the predicted mean vote during the day fluctuating from 2 to 4 units. The air change rate of living rooms in 2017 and 2019 was 0.20–2.20 h⁻¹ and 0.15–1.74 h⁻¹, respectively. Residential ventilation times detected by an air-tightness detector ranged from 0.40–1.49 h⁻¹. Furthermore, infrared thermography (IRT) detected air leakage in the windows of the all houses in this study, as well as thermal bridges and condensation on the exterior walls of several houses. The heat transfer coefficient of the exterior walls of all houses detected by IRT was 0.25–0.74 W/(m²·K), and a significant positive correlation was observed between the heat transfer coefficient of the south wall and the window-to-wall ratio. Finally, the heat transfer coefficient of the external walls exhibited a negative but not significant correlation with indoor temperature. This study provides detailed data and guidance for improving the indoor environment of rural houses in severe cold regions.