<p> Abnormal operation of HVAC systems can lead to higher energy consumption, poor indoor air quality, thermal discomfort, and reduced productivity. However, current HVAC fault detection & diagnostics (FDD) metrics have been primarily developed for energy savings, with little consideration of the impacts on indoor air quality (IAQ). This thesis proposes a data-driven fault impact analysis framework for enhancing building IAQ. After a systematic review of fault rules from three leading vendors, a curated list of faults that influence IAQ are selected. Based on two years of time series BAS and FDD data for a federal office building, Machine Learning tools help to quantify the relationship between building operation faults and indoor carbon dioxide (CO2) levels, to help generate FDD priorities for IAQ. </p>