In the context of a network calculation the suppliers are regarded as connection elements of two nodes with a heat supply. Supplier-internal procedures of the heat supply and heat transfer to the remote heating water are not considered. Therefore, using an energy balance, the thermal behavior of the suppliers can be described by the sizes of supplied heat flow Qzu , mass flow m, entry temperature TE as well as exit temperature TA if the specific warmth of the fluid is regarded as constant:

The entry temperature of the supplier is usually the return temperature of the network and is determined by the network calculation. Therefore two of the remaining three unknown quantities must be set; the third arises from Gl. 20.38. In practice the operators of long-distance heating systems usually focus on the dimensions entry temperature1 and mass flow/flow rate.

During network calculation it must however be noted that for at least one supplier the mass flow must not be set firmly, since the program uses it in order to fulfill the mass balance between advance and return. The mass flows taken from the flow by the consumers depend on the flow temperatures reached by the consumers (see Gl. 20.36). Therefore an a priori definition of the sum of all supplier mass flows before network calculation is not permissible. The supplier, whose feeding mass flow cannot be specified in advance, is designated a regulation feeder, since the feeding mass flow of the regulation feeder balances the heat losses of the pipe system, which cannot be calculated in advance, as well as the heat losses through the losses of water of the network not considered in this model.