The aim of this work is to implement and apply a model to evaluate the thermo-fluid dynamic behaviour of district heating networks, with the help of graph theory and SIMPLE algorithm. The purpose of this implementation is to study the feasibility of the substitution of natural gas users with district heating users, in order to study the possibility of an integrate energy network analysis. The first part of the work is dedicated to the numerical implementation, with the help of software Matlab, of the physical problem. A generic network is analyzed, with consequent results and validation of the model. Once the model is validated, it has been applied to a real configuration: a case study of a gas network in an urban area.