The purpose of this paper is to offer a methodology for the evaluation of large district heating networks. The methodology includes an analysis of heat generation and distribution based on the models created in the TERMIS and EnergyPro environment. For the approbation of proposed methodology the data on large-scale Tallinn district heating system was used as a basis of case study. The effective operation of district heating system, both at the stage of heat generation and heat distribution, can reduce the cost and price of heat supplied to the consumers. It can become an important factor for increasing the number of district heating consumers and demand for the heat load, which in turn will allow installing new cogeneration plants, using renewable energy sources and heat pump technologies