Croatian methodology for calculation of energy performance of buildings is largely based on the first set of CEN EPB standards (ed.2008). As these standards were proved not to be unambiguous enough for direct use, the national calculation methodology was developed in 2011. in the form of so-called Algorithms (Figure 1) by the University of Zagreb. Five Algorithms1 are written as a spreadsheet ready ‘array’ of formulas with the accompanying text describing sources for input parameters and connections with other parts of calculations. The Algorithms were initially employed for energy certification of buildings purposes. Later in 2014. they were referred to in the Technical regulation. Since then, the Algorithms have been also used for verifying the minimum requirements on energy performance (i.e. for obtaining building permit), for assessing the feasibility of alternative systems and for reporting the cost optimal levels of minimum energy performance requirements.