The present study addresses the growing significance of renewable energies as a replacement for conventional gas and oil heating systems. Given the dynamic nature of these renewable energies, the integration of thermal simulations into building planning is becoming increasingly important. However, a significant portion of German standards remains static, especially the heating load calculation according to DIN EN 12831-1:2017-09. As the norm calculates the heating performance based on the day with the lowest temperatures, there is a risk that, among other things, the supply temperature will be incorrectly designed on milder days. The heating curve plays a crucial role, but it is usually adjusted only after the building's heating system is installed.