This paper presents the results of a number of measurements that were carried out in order to quantify the ventilation efficiency of different types of windows under buoyancy ventilation. The tested window types were double vertical slide window, turn window, tilt window, awning window, horizontal pivot window and vertical pivot window. Each testing of these types comprised different opening rates, so that the performances could be compared across a wide range of window states. Performance criteria were the mass flow, the air change rate and the CO2 removal rate, each of them normalised to a temperature difference of 1 K. The horizontal pivot window turned out to be the best performing type of window. (C) 2013 Elsevier B.V. All rights reserved.