In natural ventilation systems, fresh air is often provided through opening of windows, andthere is a wide range of possibilities with regard to selection of window type and position inthe facade. Different window types have quite different characteristics and thereby differentimpact on the thermal comfort conditions in the occupied zone. The thermal comfort is alsovery dependent on the selected natural ventilation strategy, the outdoor conditions and theavailable pressure difference across the window opening. A combination of different windowtypes and windows in different positions in the same natural ventilation design should, byusing their strong sides, be capable of both improving ventilation capacity, thermal comfortand IAQ.The paper describes the results of laboratory investigations in a mock-up of an office spacewith the purpose of investigating the impact of different opening strategies on thermalcomfort conditions in the occupied zone. The results show that different window openingstrategies result in quite different airflow and thermal comfort conditions. The conditions area result of a multivariable impact, and detailed descriptions of the flows involved arecomplex.