The main aim of ventilation systems in dwelling buildings is to ensure optimal comfort conditions and indoor air quality (IAQ) for inhabitants. While temperature and humidity level are crucial indicators for human comfort, CO2 concentration is significant factor for human health. Since PVC windows have got wide expansion the problems with IAQ became more urgent. The air-exchange rates in dwelling buildings commonly are calculated by the same methods irrespective of the apartment’s level. This paper is devoted to modeling of air exchange rates in multi-storey apartment buildings. A stack effect could be observed in the multi-storey buildings during the winter: the cold outdoor air infiltrates through the lower levels of building and comes out through the upper levels. When internal walls and ceilings are not airtight, in addition to heat circulation, CO2 circulation from building’s lower levels to upper levels is also taking place. In such case the calculation methods of air-exchange rate should differ for upper and lower building’s levels. The paper provides the results of monitoring of the IAQ features in multi-storey dwelling buildings paying particular attention to the influence of building’s level on IAQ parameters. On the basis of the measurement results the simulation of air-exchange rates for different building level was done.