Certificate for energy performance of buildings is document that is issued for new buildings based on a design project after completion, where as for existing buildings based on energy audit. These certificates are issued by companies with License for performance of energy control. With these documents is also shown the nominal energy demand for heating of the building, that is basis for determining the energy class that can be from A+ as best, down to G as the least efficient. The Certificate also states the calculated CO2 emission annually, based on the building exploitation. The Certificates for energy characteristics of buildings are mandatory part of the documentation for getting a usage permit.