Heat transfer processes in buildings are always unsteady at real conditions. On the other hand practical calculations of heat exchange processes in buildings are based on steady-state process equations. In spite of modern microclimate system management, according to practical observations and theoretical investigations, undesirable changes of indoor heat behaviour occur. Such changes have negative influence on indoor heat comfort and misrepresent real energy demands of a building. The problem is influenced by factors, which have impact on thermal mode of a building. Solving of this problem involves identification and quantitative analysis of these factors. This might be useful in predicting and minimising negative influence of these factors on building microclimate and energy use.