In all advertisements for the sale and lease of real estate you will see the following entries " index of energy consumption in kilowatts 1 sq.m. per year "and" class energy saving . " It is preparing by the expert after studying the state of the property (the presence of heaters , the technical conditions of the building , the windows , the presence of thermal bridges that increase heat loss) . These data will help you quickly understand how much is spent on heating the property . Energy efficiency class ranges from A ( highest) to G ( lowest) , the higher the class , the better insulated the building and the less energy spent on heating. This certificate is required for the transaction as a purchase or rental. Its validity in the constancy of performance of 10 years from date of issuance.