This paper presents an energy performance assessment of airflow windows with a built-in roller blind integrated in a narrow office building. The paper focuses on the use of optimal solutions to improve the performance of airflow windows for typical Belgian climatic conditions. First, the influence of changing the airflow window settings—the control of the airflow rate and the recuperation of the exhaust air—is studied. Secondly, two airflow window properties are scrutinized: the U-factor of the outer glazing and the distribution of the airflow over the cavity. Finally, the influence of a good insulated inlet zone is demonstrated and the effect of the insulation of the return duct is highlighted. The results of the optimized airflow windows are compared against the results of non-optimized variants and against the results of traditional solutions, including high-performance glazing with interior or exterior shading device.