What Is District Heating?

District heating, also known as teleheating or, when cooling is delivered alongside it, district heating and cooling, is the centralized production of thermal energy at one or more plants and its distribution as hot water or steam through a network of insulated pipes to many buildings. Each connected building draws heat through a substation, typically a plate heat exchanger, rather than operating its own boiler. A heat network therefore separates the place where heat is generated from the places where it is consumed, which is what makes it possible to supply a city district from sources no individual building could use: a combined heat and power plant, an industrial waste heat stream, a large heat pump on a river or sewer, geothermal wells, or a solar thermal field.

The technology is usually described in generations. First-generation systems distributed steam, second- and third-generation systems moved to pressurized hot water at progressively lower supply temperatures, and fourth-generation systems operate near 50 to 60 degrees Celsius, low enough to use waste and renewable heat directly while still meeting domestic hot water demand. The IEA DHC definitions of district heating network generations set out the temperature ranges, control strategies, and building-side requirements that distinguish each step.

Network and Plant Architecture

A heat network has three parts: production, distribution, and the consumer substation. Production may be a single plant or a set of dispatchable and non-dispatchable sources feeding a common supply header. Distribution uses a buried twin-pipe or single-pipe pair, with pre-insulated steel or polymer carrier pipes, expansion provisions, and leak detection wires embedded in the insulation. Supply water is pumped out, gives up heat at each substation, and returns cooler. Return temperature is the network's key performance variable, since a low return improves flue gas condensation, heat pump coefficient of performance, and storage capacity all at once. Sizing is governed by simultaneity of demand across connected buildings, which lets network capacity fall well below the sum of individual peak loads.

Control, Storage, and Sector Coupling

Heat networks are increasingly operated as flexible assets rather than fixed-output systems. Large water tanks and pit or borehole storage decouple production from demand by hours to months, so a plant can run when electricity prices or renewable output favor it. Weather-compensated supply temperature control, differential pressure control at the pumps, and predictive load forecasting at each substation together reduce pumping energy and distribution losses. Because power-to-heat units link the network to the electricity system, district heating provides a route for absorbing surplus wind and solar generation, a flexibility role examined in the IEA analysis of district heating in the energy transition. Network topology and pipe diameters are themselves optimization variables, and mixed-integer formulations for multi-period topology and design optimization of district heating networks are used to plan staged expansion under uncertain future demand.

Losses, Metering, and Economics

Distribution heat loss depends on pipe insulation class, supply and return temperatures, ground conditions, and linear heat density, the annual heat sold per meter of trench. Low linear heat density is the main obstacle in sparse suburbs, which is why networks are usually built out from dense loads such as hospitals, campuses, and apartment blocks. Ultrasonic heat meters at each substation measure flow and the supply-return temperature difference to bill delivered energy, and the same data stream feeds fault detection for undersized valves, bypassed substations, and stuck control valves.

Applications

District heating has applications in a range of settings, including:

• Urban residential and commercial building heat supply
• University, hospital, and military campus energy systems
• Industrial parks reusing process waste heat
• Geothermal and solar thermal community energy schemes
• Data center waste heat recovery
• District cooling networks serving air conditioning loads