Due to diverse bond patterns and large irregular geometries, traditional Chinese cavity walls—unlike European cavity walls—feature a non-vented air gap with looping air circulation and convection. Although initially designed to save bricks and improve energy efficiency, limited research has explored their hygrothermal performance and the impact of bond patterns and cavity geometry. This study addresses two key issues: first, the equivalent thermal performance of the air gap and its impact on heat transfer through wall assemblies. Second, Heat, Air, and Moisture (HAM) modeling is applied to assess whether the air gap facilitates moisture migration. Results indicate that air gap geometry affects the energy performance of the wall configuration but has a limited impact on moisture migration. While the air gap enhances the energy performance of the wall, it also introduces a higher moisture-related risk. Additionally, brick properties predominantly determine the hygrothermal performance of cavity walls. This research provides comprehensive insights into optimizing the hygrothermal performance of traditional Chinese cavity walls, contributing to the preservation and sustainable use of Chinese heritage buildings.