The continuous growth of residential buildings has led to increasing attention on energy consumption and emission reduction. Taking an old residential building in Zhengzhou as an example, this article used Dest-h to simulate and calculate its energy-savings. A nine-factor, three-level orthogonal table was designed to analyze factors such as external wall heat transfer coefficient and building orientation, to understand the impact of different factors on energy savings. The results showed that among the 27 orthogonal experiments, the cooling consumption of experiment 23 was the lowest (21,236 kWh); the heating consumption of experiment 20 was the lowest (11,376 kWh); experiment 25 had the lowest total energy consumption (37,416 kWh). The comprehensive energy-saving rate was 36.12%, 43.29%, and 49.02%, respectively, in experiments 23, 20, and 25 as compared to the existing building. The annual energy-saving benefits were 6.57 yuan/m2, 7.87 yuan/m2, and 8.91 yuan/m2, respectively. Among the nine factors studied, the heat transfer coefficients of the external wall and window had the greatest impact on the energy savings of this building. In the case of minimum total energy consumption, the heat transfer coefficient of the external wall was 0.6 W/(m2 center dot K), and that of the external window was 0.8 W/(m2 center dot K). The results prove the reliability of Dest-h in building energy conservation research, and it can be applied to practical research on energy consumption and emission reduction.