This standard specifies data and procedures for the calculation of the energy performance of buildings relating to space heating and cooling and domestic hot water production. This standard is a national guideline for immediate and univocal application of technical specifications elaborated by CEN to support the Diretive 2002/91/EC "Energy Performance of Buildings" .This Part 2 provides data and methods for the determination of: - seasonal average system efficiencies - energy need for domestic hot water production - annual specific need of primary energy for space heating and domestic hot water production.