This paper studies in three-dimension the coupled convective and radiative heat transfer rate from awindow surface with adjacent venetian blind using a commercial CFD code. For this study the window surface was modeled as an isothermal vertical flat plate. The flow patterns (temperature and velocity fields) and convective heat transfer coefficient were investigated for different blade angles (00, 450, -450, 800). Comparisons were made with experimental and other theoretical research. The results of this paper confirm that a heat transfer from a vertical flat surface is influenced by the presence of a venetian blind and that for some geometries 3D simulation is essential in capturing the air flow field.