Internal heat gains by people and equipment contribute to the heat demand of residential buildings. They increase the lower the energy requirement of a building and can account for about a quarter of the heating requirement of a KfW-55 efficiency house. They thus make a considerable contribution to reducing heating requirements, which KfW takes into account indirectly as part of its financial support. In Germany, a constant value of 5 W/m² energy reference area is assumed for residential buildings - when applying DIN V 4108-6 and DIN V 4701-10. This value has remained constant since the standards were introduced (2003), although energy-saving devices have now penetrated the market. Other calculation models and authors also assume lower profits in Europe, so that it seems justified to adjust this value. In this study, the - internal heat sources in apartment buildings in Germany - are calculated in relation to the degree of equipment, a heat loss factor and the eco-design requirements, among other things, in order to obtain a modern basis for the calculation of energy balances.