Complete knowledge about habits of the occupants, including their opinions regarding ventilation systems is an important condition for reducing the consumption of natural resources and improving indoor comfort. In addition, uncomforted occupants tend to take measures to improve their situation, which may increase energy consumption. Advanced thermal models for buildings can perhaps predict interactions between the IAQ determinants, e.g. energy consumption, ventilation and comfort, but do not take into account the behavior of residents. By questionnaires and physical measurements this study evaluated dwellings equipped partly with centralized and partly with decentralized ventilation systems with heat recovery. This field study involved two post-occupied residential buildings situated in the city of Esch-sur-Alzette, Luxembourg, during spring season 2015. Thus, both the physical measurements and questionnaires were considered. The results obtained demonstrated that more than 80% of the residents were satisfied and the perceived IAQ was judged "normal", "good" or even "very good". Furthermore, the measurements performed detected in some cases malfunction of ventilation devices, wherefore the occupants were unable. (C) 2017 Elsevier B.V. All rights reserved.