Increasing the level of thermal resistance of the building envelope in combination with the choice of heat source is an urgent task. It is important to take into account changes in the cost of energy over time. Thermal modernization, in its turn, allows to increase the level of thermal comfort, which is not taken into account and evaluated in practice, although the relevant standards for comfort conditions and categories of buildings to ensure comfort have been introduced in Ukraine. This paper analyzes the change in the level of comfort after thermal modernization, determines the category of the building to provide comfortable conditions, as well as identifies the change in the average radiation temperature of the fences, as one of the main factors of PMV change in these conditions.