Existing and designed residential buildings should provide the residents with appropriate indoor microclimatic conditions. Both in terms of thermal comfort and indoor air quality. Strong tendencies towards saving energy in buildings contribute to the use of materials with better thermal insulation (walls) and airtightness coefficients (doors and windows). In the last few years there has been a tendency towards air-tight sealing of buildings. This phenomenon can be seen both in older buildings being refurbished as well as in those that are new or thermally-upgraded. At the same time, in existing and new buildings traditional, gravity ventilation is used, and is becoming an extremely important factor in achieving the required indoor conditions. The following are some of the results of the research on this subject, which will, hopefully, provide new insight. The paper describes the use of new technologies, such as hybrid ventilation, in existing buildings. The results presented herein have been achieved from comprehensive measurements in the buildings with natural and hybrid ventilation. The aim of the paper is to present and summarize preliminary studies describing the influence of natural and hybrid ventilation as well as airtightness on an indoor environment.