The effect of low ventilation rates (1 or 0.5 air change per hour) on thermal comfort and ventilation effectiveness was experimentally studied in a simulated residential room equipped with radiant floor heating/cooling and mixing ventilation systems. The tests were performed for various positions of supply and extract air terminals and different winter and summer boundary conditions. Vertical air temperature, operative temperature and air velocity profiles were measured in different positions in the room, and equivalent temperatures were derived, in order to characterize thermal comfort. Contaminant removal effectiveness (CRE) and local air change index was measured in order to characterize ventilation effectiveness in the occupied zone. Acceptable thermal comfort was found in most experiments; however, air temperature differences higher than 3 degrees C occurred when floor cooling was combined with unconditioned outdoor air supply, i.e. at the supply air temperatures higher than the room air temperature. Moreover, low floor temperatures were needed to maintain the desired reference temperature in the stratified thermal environment. Mainly in cooling conditions the ventilation effectiveness depended on the positions of supply and extract air terminals and on the difference between the supply and the room air temperature, and it could be as low as 0.5, where 1 is complete mixing. (C) 2013 Elsevier B.V. All rights reserved.