<p>With buildings accounting for 30% of global energy use, improving operational energy efficiency is critical to achieving climate goals. In addition to conventional retrofitting strategies, Building Automation and Control Systems (BACS) offer significant potential to reduce energy use while preserving comfort. The European standard EN ISO 52120–1 supports BACS integration using the BAC-factor method, a simplified, factor-based estimation of energy savings. However, these generic efficiency factors do not account for variations in building typologies and building characteristics, this variability has not been systematically quantified. This study provides an innovative simulation-based approach for an initial exploration of the variance in BACS savings, over multiple office typologies and building characteristics. Simulated savings show large variability across different BAC functions: 19–71% for heating emission control, 1–58% for cooling emission control, 6–46% and 4–94% respectively for heating and cooling energy in ventilation control, 14–65% for lighting energy control, and -27–74% for cooling energy with shading control. Analysis of variance (ANOVA) and effect size analysis are used to quantify how key building characteristics, i.e. typology, window-to-wall ratio, and envelope insulation, drive the variability of BACS energy savings. The findings provide quantitative evidence that BACS performance is highly context-dependent and that a uniform, fixed-factor approach like the BAC-factor method fails to capture this diversity. These findings emphasize the importance of developing context-aware evaluation methods that account for building-specific characteristics to more accurately predict BACS energy savings.</p>