The characteristics of autoclaved aerated concrete blocks was tested and analyzed in comparing with Standards’ requirements. The results of the study show that the actual thermophysical characteristics of autoclaved aerated concrete blocks, cut from product samples of the three largest manufacturers, in most cases do not coincide with the values declared by the manufacturers and presented in the standards prepared with their direct participation. The mismatch between the calculated and actual values of the thermal conductivity of materials and products used in the installation of external walling, leads to an increase in transmission heat losses through the external walls and the waste of thermal energy for heating and ventilation of buildings. In this regard, a radical review of the values declared by manufacturers, as well as the standards on the basis of which the products are manufactured, and their correct presentation in the current regulatory documents are required.