This master's thesis is concerned with calculations of the energy needed for the heating of multi-apartment buildings, and application of the results obtained by means of such calculations when preparing energy performance certificates, as well as with the determination of the location correction factors which are needed to take into account the different positions and aspects of individual parts of such buildings. The suitability of currently valid calculation methods was analysed by performing detailed calculations for three actual but differently designed multi-apartment buildings. In the first step a detailed analysis of all the applicable European and Slovenian laws and regulations was performed. The energy needed to heat each apartment was then calculated using the KI Energija 2014 programme, firstly by means of the more accurate method defined by the European standards, and secondly by using the simplified method which is permitted by the Slovenian guidelines. The main difference between these two methods is related to the occurrence of heat losses via unheated spaces, which are treated in a very simplified way in the Slovenian guidelines. This means that results obtained using these guidelines are inappropriate, since they vary considerably from the values obtained by using more detailed values. For this reason it is proposed that a correction should be made to the method of calculation, which is relatively simple to implement but provides more accurate results. The same technique was used for the correction factors that were defined, in three different ways, for all of the investigated apartments. This method gave the best results, since it takes into account the effect of solar gains which the Slovenian method completely neglects. However, the final adjustments do not exceed the reasonably acceptable values. This master’s thesis therefore presents some updated calculation methods which can be used to achieve greater accuracy, and also fairer results for different apartment owners.