Control strategies for operating district heating, the utilization of biomass boilers under optimal conditions, estimation of solar production by central solar-heating systems and much more, demand realistic modelling of heat loads/demands for district-heating systems. A dynamic system model is presented: the results from this simulation were then compared with results from alternative methods found in the literature. If knowledge is available for a given case or the load is to be found for a new system, the simulation approach is recommended. The method, however, involves many parameters that can lead to errors and uncertainties. Therefore, if knowledge of case-specific parameters is rare, the degree-day method can lead to realistic results. For low-energy, solar-optimized building area, the energy-signature method leads to reasonable results and if system-wide load data are available, the energy-signature method can even do better than the degree-day method.