The main aim of the work is to investigate unsteady indoor thermal factors’ influence on premises microclimate, energy demand and installed heat power. Tasks of the work: 1. To investigate evaluation methods of thermal characteristics of a building which have influence on unsteady heat transfer, and to point out the main and determining factors. 2. To investigate dynamic thermal characteristics of a building in an experimental way. 3. To describe unsteady heat transfer processes in buildings on the basis of energy conservation law for a control volume with the help of active heat capacity conception and to adapt calculation methods for practical use. 4. To estimate the influence of active heat capacity on premises microclimate, design heat power and energy use.