The article summarizes the IAQ parameters of multi-apartment buildings before and after renovation in Latvia. In a building with natural ventilation system air exchange is significantly dependent on the position of the apartment within the building. If CO2 as an indicator of indoor air quality is analyzed, the results show that inhabitants’ behavior has a considerable impact on IAQ. The planning of adequate investment in buildings to improve energy efficiency and choosing the modern, adequate and effective engineering solutions, it is possible to raise the comfort level of living space and to reduce heat and thermal energy consumption.