District heating network · Glossary

A district heating network is a pipe infrastructure that transports heat from one or more generation plants to several buildings or businesses. Hot water is usually the heat carrier, less often steam. It flows through insulated pipes. In the connected buildings, the heat is made usable for space heating, hot water or industrial processes via a heat interface unit. The network itself is not an energy source but the transport system for the district heating that is delivered.

Technically, a district heating network usually consists of a flow line and a return line. In the flow line, hot water reaches the customers. There it releases its heat to the building's heating system via a heat exchanger. In the return line, the cooled water flows back to the generation site. You can picture it as a circuit in which the water delivers the heat and travels back empty. The amount of heat delivered is measured in kilowatt-hours. The connection capacity (also called connected load), by contrast, is stated in kilowatts. It describes the maximum thermal output a building can draw from the network. This distinction matters for prices, network design and security of supply: even a building with moderate annual consumption can need a high peak output on cold days.

Distinction from district heating, local heating and building networks

The district heating network is the infrastructure; district heating is the product delivered. A network can extend over many kilometres in a large city, supply a neighbourhood or connect only a few buildings. The term local heating is often used for smaller, locally limited networks, but it is defined sharply neither technically nor legally. German building energy law does not distinguish between local and district heating. It speaks generally of heat distributed via a heat network.

In Germany, the boundary with the building network is drawn more clearly in law. Under section 3(1) no. 9a of the building energy law, a building network supplies heat and cooling exclusively to at least two and at most 16 buildings and at most 100 residential units. Since the end of July 2026, this law has been called the Gebäudemodernisierungsgesetz (GModG, Building Modernisation Act), previously the Gebäudeenergiegesetz (GEG, Building Energy Act). If either of the two limits is exceeded, it is a heat network. Whether all buildings are located on one plot of land plays no role for this definition. A heat network is therefore a pipe-bound supply facility that is not a building network. A district heating network generally falls under this term. The distinction is important because technical requirements, funding logic, price oversight and municipal planning apply differently depending on the category.

District heating networks are also easily confused with heat generation plants. Whether the supply is climate-friendly, expensive, flexible or fossil-based depends on the connected sources and on operation. A network can, for example, be fed by combined heat and power with coal or gas, by gas-fired heating plants, waste incineration, industrial waste heat, geothermal energy, biomass, solar thermal energy, large-scale heat pumps or power-to-heat plants. The same pipeline can carry very different generation structures over decades.

Why the temperature level determines the possibilities

A key technical characteristic is the temperature level. Older networks often operate with high flow temperatures, in some cases above 100 degrees Celsius. This makes it easier to supply unrenovated buildings and some process heat applications. However, high temperatures cause greater heat losses and make it harder to integrate low-temperature sources. River water, wastewater, data centres or solar thermal energy often supply heat at a lower level. This heat then has to be raised to the required temperature using heat pumps. The greater this temperature difference, the more electricity the pumps need.

Lower network temperatures reduce losses and widen the range of possible renewable or unavoidable heat sources. In return, they require suitable building technology, sufficiently large heating surfaces, good control and a hydraulically stable network design. A low return temperature is particularly important. If the return is too warm, heat pumps, condensing technology and storage work less well, and more water has to be pumped through the pipes for the same amount of heat. A district heating network is therefore shaped not only by the generation plants but also by the connected buildings.

Network losses are also part of technical reality: heat is lost to the ground through the pipes. In dense urban areas with many customers per metre of pipe, these losses weigh relatively less than in sparsely built-up areas. Heat density, that is, heat sales per metre of pipe, is therefore a key technical and economic variable.

Significance for the power system and the heat transition

District heating networks couple heat supply with electricity generation or electricity consumption. In classic networks, combined heat and power (CHP) plays a major role: a power plant produces electricity and heat at the same time, and the waste heat from electricity production is fed into the network instead of being released into the environment. This makes better use of the fuel but ties electricity and heat generation together. If a CHP plant has to run because of heat demand, it also generates electricity when the power system needs no additional feed-in.

With more wind and solar power, this role shifts. Large-scale heat pumps and electrode boilers convert electricity into heat. A heat storage unit separates generation and consumption in time: heat can be produced when electricity is cheap or abundantly available from renewables, and is delivered later. However, this flexibility does not arise merely from the network connection. It requires suitable plants, storage, sufficient connection capacity to the electricity grid, appropriate market rules and operational management that responds to electricity prices, bottlenecks and heat demand.

For the heat transition, district heating networks are of interest above all where solutions for individual buildings reach their limits. In densely built-up neighbourhoods, space for geothermal probes or outdoor units is often lacking, and historic buildings can often only be renovated step by step. Large shared sources such as deep geothermal energy, wastewater, river water or industrial waste heat only become usable for many customers in the first place via a network.

Legal framework in Germany (as of November 2026)

The Heat Planning Act (Wärmeplanungsgesetz, WPG) prescribes minimum shares of annual net heat generation for every heat network. They must come from renewable energies, unavoidable waste heat or a combination of the two. The following applies to existing networks:

At least 30 percent from 1 January 2030 and at least 80 percent from 1 January 2040 (section 29(1) WPG).
On application, the competent state authority can grant extensions of the deadlines until the end of 2034 and the end of 2044 respectively. The prerequisites are undue hardship and a roadmap for the expansion and decarbonisation of the heat network. Separate rules apply to complex measures: they must be notified by the end of 2026, and construction must have begun by the end of 2027.
Exceptions exist, among others, for networks that supply almost exclusively commerce or industry with process heat. A special rule applies until the end of 2034 to networks fed predominantly by subsidised fossil CHP. The Länder may set higher shares.
Connected customers can demand proof of compliance from the operator. If the requirements are missed other than temporarily, they generally have a right to disconnect in order to supply themselves with renewable heat. A mandatory connection and use requirement (Anschluss- und Benutzungszwang) remains unaffected.

In building law, the framework shifted in 2026. The Gebäudemodernisierungsgesetz has applied in its essential parts since 29 July 2026 and has replaced the Gebäudeenergiegesetz. As a result, the previous obligation to operate new heating systems with 65 percent renewable energy has also been dropped. Under that obligation, connection to a heat network was an important compliance option. How the abolition will affect demand for connections remains open.

The AVBFernwärmeV (General Terms for the Supply of District Heating) still applies to supply contracts for the time being. On 26 August 2026, the Federal Cabinet adopted key points for a heat network package. Under these, the AVBFernwärmeV and the Fernwärme-Verbrauchserfassungs- und Abrechnungsverordnung (FFVAV, District Heating Consumption Metering and Billing Ordinance) are to be merged into a new Heat Network Act. Price adjustment clauses are to continue to contain a cost element and a market element. Until a law is passed, these are only plans.

Economic and institutional particularities

A district heating network requires high initial investment and is used for a long time. Pipes, pumping stations, generation plants and storage are built for decades, and a large share of the costs is fixed. Once the network exists, each additional connection to an existing pipe has to be assessed economically differently from a new route. This creates strong path dependencies: today's routing, temperature level and connection rate determine how the network can be decarbonised later.

For customers, district heating is a special form of supply. In a given network there is generally no competition among several suppliers in the same pipe; the supplier has a local monopoly. Price formulas, transparency, contract terms, mandatory connection and use requirements and municipal oversight are therefore not side issues. They help decide whether district heating is accepted as reliable infrastructure.

Municipal heat planning makes district heating networks more plannable but does not replace an economic and technical assessment. A designated heat network area means neither that every street will soon be connected nor that district heating is the cheapest solution for every building. Conversely, an area without a network today may be suitable later. Conflicts often arise when owners want to invest in their own heating systems while the municipality envisages a later network solution. In that case, clear timetables and reliable commitments on expansion count for more than general target visions.

Common misconceptions

District heating is not automatically climate-neutral. This is only the case if the heat comes from renewable sources or unavoidable waste heat and the emissions are properly accounted for. A network operated predominantly with fossil CHP or with boilers can have advantages over old individual heating systems, but its emissions depend on the fuel and on operation. The statutory minimum shares from 2030 show that many networks still face this transformation.

Waste heat, too, is often treated too simply. It is valuable because it would otherwise be lost, but it is not always free of charge, permanently available or suitably tempered. Industrial processes can change, businesses close, and data centres have to be integrated contractually. Anyone using waste heat must clarify availability, output, temperature, redundancy and ownership boundaries.

Finally, a large network is not automatically more efficient than decentralised heat pumps. In dense areas with suitable sources it can make a lot of sense. In sparsely populated areas, pipe losses and investment costs can eat up the advantages. Whether a network is worthwhile therefore does not depend on the technology as such but on the interplay of settlement structure, building stock, heat sources, electricity grid, prices and the operator's capability. A district heating network is thus not an enlarged heating system but a supply network. Its benefit arises only when sources, pipes, buildings, prices and public planning fit together.

Sources

Wärmeplanungsgesetz (WPG) § 29 Anteil erneuerbarer Energien in Wärmenetzen — Bundesministerium der Justiz / Bundesamt für Justiz (gesetze-im-internet.de); unbekannt (konsolidierte Fassung, abgerufen 11.11.2026). § 29 Abs. 1 bis 9 WPG
Gebäudeenergiegesetz (GEG): Wie definieren sich Wärmenetze und Gebäudenetze? — Bundesministerium für Wohnen, Stadtentwicklung und Bauwesen (BMWSB); unbekannt. Abschnitt c) Wie definieren sich Wärmenetze und Gebäudenetze?
GModG-Infoportal – Glossar: Gebäudenetz — Bundesinstitut für Bau-, Stadt- und Raumforschung (BBSR); unbekannt. Glossareintrag Gebäudenetz, Verweis auf § 3 Abs. 1 Nr. 9a GModG
Neues Gebäudemodernisierungsgesetz in Kraft getreten — Presse- und Informationsamt der Bundesregierung; 2026-07-29. Einleitung und Abschnitt zum Gesetzgebungsverfahren
Wärmenetzpaket statt AVBFernwärmeV-Novelle: Was sich für Wärmelieferverträge ändert — Energie und Recht (Fachblog einer Kanzlei); 2026-08-27 (Sachstand). Einleitung und Abschnitt zur Preisänderungsklausel

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Edited by eCMS on 11.11.2026 19:47