Experimental and data-driven characterization of window-induced air leakage in residential buildings

Windows contributes up to 40% of envelope heat losses and around 9% of total building energy consumption due to air leakage. In the U.S., 48 million homes still use single-pane windows. Although approximately 29 million retrofit projects and 24 million new constructions occur annually, only about 4 million homes replace windows each year, in part due to limited information on the potential energy savings of high-performance windows. To address this gap, this study generates empirical evidence by (1) evaluating the contribution of windows to whole-building air leakage in 20 residential buildings using blower door tests before and after window replacement and (2) assessing whether building and window characteristics influence the measured change. Most simulation studies assume that replacing windows not only lowers the U-factor but also reduces air leakage by 10-20%. However, this assumption lacks empirical validation, highlighting the need for experimental analysis of air leakage specifically associated with windows. Using blower door tests in accordance with ASTM E779-19 , the results indicated an average reduction in air infiltration of 6.1% within the range of 0.5-19.30% across all buildings and no significant correlations were found between air leakage improvements and any building/window characteristics. This research aims to help homeowners, energy modelers and policymakers to provide empirical data on importance of upgrading to more energy-efficient windows, supporting energy-efficient building standards.