In the design of natural ventilation systems, there is a wide range of possibilities with regard to the selection of window type and the positioning of windows in the facade. Each window type has unique characteristics, which affect air flow and thermal comfort conditions in the occupied zone. A combination of various window types and faade locations in a room should be capable of improving thermal comfort and minimising draught risk. This paper describes the results of laboratory investigations in a mock-up of an office space with the purpose of investigating the impact of different opening strategies on thermal comfort conditions in the occupied zone. The results show that different window opening strategies result in quite different air flow and thermal comfort conditions. The conditions are a result of a multivariable impact, and thus detailed descriptions of the flows involved are quite complex.