Optimal design and management of DH networks require numerical models for simulating the physical behavior of the network in various operating conditions. DH network models usually rely on the physical description of the fluid-dynamic and thermal behaviours. The use of physical models can represent a limitation in various cases: a) when extended networks are considered (several thousands of nodes); b) when multiple simulations are required in real-time; c) when multi-energy networks are optimized. In these cases, compact models are preferable. This work aims at presenting the compact model for fast simulation of thermal transients. The model preserves the reliability of a physical model because it solves the mass and energy equation. Only the momentum equation is simplified in order to overcome complexity related to the iterative solution of mass and momentum equations, which are coupled. Results of the application to a real network show that the proposed methodology significantly reduces computational costs with respect to a complete physical model, with small impact on the accuracy. The approach is suitable for being used in combination with other network models (gas, electricity) and with models of other energy infrastructures, such as plants, storage units or energy conversion systems. (C) 2019 The Authors. Published by Elsevier Ltd.