In Eastern Europe countries, including Ukraine, a significant part of the buildings belongs to the mass development of the 80s, which are characterized by a low level of energy efficiency. For such countries with sharply continental climates, heating costs prevail to a large extent. Improved thermal protection forces more attention to be paid to heat losses with ventilation. The distribution of air exchange between individual rooms is difficult to determine, especially due to natural ventilation. The work is devoted to considering the conditions of natural convection and determining the effect on the energy consumption of a building. The article considers the advanced ASHRAE technique for calculating natural air exchange. The influence of the temperature and wind characteristics of the outdoor air on the natural component of the air exchange rate at the different locations of the representative rooms of an 8-story building is analyzed. The value of the air exchange rate for typical conditions of Kiev does not exceed 0.25 h-1, 0.65 h-1 and 0.4 h-1 for two-chamber and single-chamber double-glazed windows, triple glazing in wooden double binders, respectively. On the first floors, air exchange is associated with air infiltration, and on the last floors there is exfiltration, which must be taken into account when dynamically modeling the energy characteristics of a building. The example is with additional mechanical ventilation to maintain a comfortable environment. 5R1C dynamic grid models were created to study the energy performance of the building. The estimate of additional heating costs due to infiltration is 23 % for the North and 43 % for the South orientation of rooms with two-chamber energy-saving windows. It has been established that in dynamics, the energy consumption of a building with normative air exchange and the calculated value of the natural component differs by 50–75 %, which is a possible level of savings under actual air exchange conditions in comparison with standard ones. This savings can be reduced by increasing air exchange during busy hours, for example, due to additional aeration.