Natural ventilation has great potential to create desirable indoor air quality and reduce energy consumption in buildings. Accurately modeling the windows of buildings is important to quantify airflow in single-sided natural ventilation. However, a simplification of real windows into rectangular openings has been widely applied in published literature, which seriously affects predictions of airflow through real windows. This investigation numerically evaluates the performances of real windows in the case of buoyancy-driven, single-sided ventilation. Several typical windows used in buildings are analyzed. The Reynolds-averaged Navier-Stokes (RANS) model and k-omega turbulence model are combined to solve airflow characteristics inside and outside the building. The results reveal that the computational fluid dynamics (CFD) model is sensitive to computational domain sizes and boundary conditions, while the sensitivities for different window configurations are different. The ventilation rates and thermal profiles inside the building varied for each window type, although the open window areas are almost identical. According to the comparison of CFD and analytical methods, it was found that the specification of constant discharge coefficients is no longer suitable to estimate the ventilation rates through real windows, and further investigations are needed to find better estimates of the coefficients for a particular window configuration. (C) 2017 Elsevier B.V. All rights reserved.