This European Standard defines a method for calculation of the energy requirements, electricity production, thermal output and recoverable losses of building-integrated cogeneration units forming part of a heat generation system (space heating and domestic hot water) in a building. Such units are commonly known as micro- or small scale cogeneration, or micro- or small scale CHP. The calculation is based on the performance characteristics of the units, defined in product standards, and on other characteristics required to evaluate the performance of the units as included in the technical building system. The test of building-integrated cogeneration units for heating systems may be worked out in a national annex. As soon as European test methods are available these should be used. NOTE Primary energy savings and CO2 savings, which can be achieved by cogeneration units compared to separate production of heat and consumption of electricity, are calculated according to prEN 15603. Indications about the savings calculations are given in informative Annex C.