Glossary

The proposed test for which existing non-domestic buildings must connect in a zone: a wet heating system and average heat demand above 100 MWh a year (100,000 kWh). Where metered data is missing, demand will be estimated using energy-density benchmarks for the building's use type.

See Heat demand, Wet heating system, Benchmarking, Requirement to connect · Source

The proposed period of 6 months from receiving a connection notice. In this time you either agree a connection date with the zone developer or apply for a temporary exemption.

See Connection notice, Connection window, Temporary exemption · Source

A network that circulates water at low temperatures, close to ground temperature, with a heat pump in each building raising it to a useful temperature. It can move heat between buildings that need cooling and buildings that need heating.

See Heat pump, Heat network, Flow and return temperatures

The Ofgem regime that heat network suppliers and operators work under, with authorisation conditions applying from 27 January 2026. Existing networks must register with Ofgem by 26 January 2027.

See Ofgem, HNTAS · Source

Comparing a building's energy use with typical figures for similar buildings. Under the zoning proposals, where metered data is missing, heat demand will be estimated using energy-density benchmarks for the building's use type.

See Heat demand, 100 MWh threshold, Degree days · Source

A heat network serving several buildings on one site run by a single organisation, such as a university, hospital or business park. The government intends to extend the requirement to connect to buildings containing an energy centre that supplies a campus network. This is proposed policy.

See Energy centre, Requirement to connect, Heat network · Source

The consumer advocate for heat network consumers in England and Wales, a role it took on from 1 April 2025. Heat network customers can go to it for free advice about bills or supply problems.

See Energy Ombudsman, Ofgem, Heat Trust · Source

Plant that generates electricity and captures the heat produced at the same time, so the heat can be used in a heat network. Many older networks use gas-fired CHP; newer networks increasingly use low-carbon heat sources instead.

See Energy centre, Heat pump, Energy from waste

A heat network within a single building, where one central plant heats many flats or units. Under the zoning proposals, existing buildings with communal heating, both domestic and non-domestic, would be required to connect in a zone.

See Heat network, Requirement to connect, Heat interface unit (HIU) · Source

A proposed exemption from the requirement to connect on set grounds: existing low-carbon heating with an expected lifespan of more than 2 years, legal or contractual barriers, building safety remediation, permanent physical barriers, technical incompatibility, or conservation.

See Temporary exemption, Requirement to connect, Crown body · Source

A one-off payment to connect a building to a heat network, usually covering the pipework into the building and the substation or HIU. Amounts vary widely by building and network, so ask for the basis of any figure in writing.

See Standing charge, Substation, Connection notice

The formal notice telling a building owner their building must connect to the zone's heat network. Under the proposals, the zone coordination body issues it within 2 weeks of the zone developer's request, and receiving it starts the 6-month agreement phase.

See Agreement phase, Connection window, Zone coordination body, Temporary exemption · Source

The period in which a building is expected to connect to the zone's network. Under the proposals it is at least 12 months long and can run at the same time as the 6-month agreement phase.

See Agreement phase, Connection notice, Temporary exemption · Source

Heat networks: Code of Practice for the UK, the industry's main standard for designing, building and running heat networks, published by CIBSE with the Association for Decentralised Energy. CP1.2 is the common name for its second edition. Ask designers and operators whether they work to it.

See HNTAS, Heat losses, Flow and return temperatures

An organisation with Crown status, such as many central government departments. Zoning law does not apply to bodies with Crown status, though the government says it is exploring legislative changes that could bring Crown bodies in later.

See Requirement to connect, Conditional exemption · Source

Heat removed from servers by a data centre's cooling systems. It is relatively low temperature, so it is usually boosted with heat pumps before being supplied to a heat network.

See Waste heat recovery, Large-scale heat pump

A measure of how cold a period was, based on how far outside temperatures fell below a set base temperature. Facilities teams use degree days to compare heating use between years or sites with the effect of the weather taken out.

See Heat demand, Benchmarking

The Department for Energy Security and Net Zero, the government department responsible for heat network policy, including zoning. It published the government response on zoning on 21 January 2026.

See Heat Network Zoning Authority, Heat Networks Delivery Unit (HNDU), Energy Act 2023 · Source

The law that gives the government powers to create heat network zones in England, in Part 8, Chapter 2 (sections 226 to 237). It became law on 26 October 2023, but zoning cannot work until regulations are made under it.

See Zoning regulations, Heat network zoning, DESNZ · Source

The building or plant room where a heat network's heat is produced. It holds the heat pumps, boilers, CHP engines or thermal stores, plus the pumps that push hot water around the network.

See Heat network, Thermal store, Large-scale heat pump, Combined heat and power (CHP)

Plants that burn non-recyclable waste to generate electricity. Many can also supply heat to a nearby heat network, which makes much better use of the energy they produce.

See Waste heat recovery, Combined heat and power (CHP), Energy centre

The Energy Ombudsman accepts heat network disputes, usually after 8 weeks with the supplier. It began accepting heat network complaints on 1 April 2025.

See Citizens Advice, Ofgem, Heat Trust · Source

Energy services company: a company that builds, owns or runs energy plant and sells the energy to customers, rather than each customer owning plant. Many heat networks are run by an ESCO, sometimes jointly owned with a council.

See Zone developer, Standing charge, Connection charge

Flow temperature is the temperature of water leaving the heat source; return temperature is the temperature when it comes back. Low-carbon networks often run cooler than old boiler systems, so some buildings need radiator or control changes to work well.

See Wet heating system, Substation, Heat losses

A government capital grant scheme supporting new and existing low- and zero-carbon heat networks in England. Check GOV.UK for current funding rounds and eligibility, as these change.

See Heat Networks Delivery Unit (HNDU), Warm Homes Plan

A small device fitted to a radiator that records its relative heat output, used to split a building's heat bill between occupants. Amendments from 27 January 2026 removed the requirement to fit them under the metering and billing regulations.

See Metering and billing regulations, Heat interface unit (HIU) · Source

The amount of heat a building actually uses for space heating and hot water over a period, usually given in kWh or MWh a year. For a building with gas boilers it is lower than the gas consumption on your bills, because some of the energy in the gas is lost in the boiler.

See Megawatt-hour (MWh), Kilowatt-hour (kWh), 100 MWh threshold, Benchmarking

A compact unit, usually in each flat or individual unit, that takes heat from the network and provides space heating and hot water. It typically contains a heat exchanger, controls and often a heat meter.

See Substation, Communal heating, Primary and secondary side

Heat that escapes from pipes between the energy centre and the customer. Poorly insulated, oversized or underused pipework increases losses, which raises running costs and can push up what customers pay.

See Flow and return temperatures, CP1 code of practice, Standing charge

A system of insulated pipes that carries heat, usually as hot water, from a central source to several buildings or homes. Each building takes heat through a substation or heat interface unit instead of running its own boilers. Heat networks supply about 3% of UK heat demand today.

See Communal heating, Energy centre, Heat network zoning · Source

A designated area where one zone developer builds the heat network and certain buildings can be required to connect. No zones have been designated yet: none can be until the zoning regulations are in force.

See Heat network zoning, Zone designation, Zone developer, Zone delivery area · Source

The policy of designating areas of England where a heat network is expected to be the lowest-cost way to decarbonise heat, then requiring certain buildings to connect. The powers are in the Energy Act 2023 but the detailed rules are proposed and wait for regulations. It applies in England only.

See Heat network zone, Energy Act 2023, Zoning regulations · Source

The national body that will oversee heat network zoning in England. Under the proposals it sits within DESNZ at first, then moves to the Warm Homes Agency once that is set up.

See Zone coordination body, DESNZ, Warm Homes Agency · Source

Government work with 28 towns and cities in England to test zoning methods. Being on the pilot list does not mean a zone has been designated.

See Zone designation, Zone opportunity area, Heat Networks Delivery Unit (HNDU) · Source

Scotland's own heat networks law, which includes its own zoning regime. English zoning under the Energy Act 2023 does not apply in Scotland. Wales has no zoning regime.

See Energy Act 2023, Heat network zoning · Source

A DESNZ team that supports local authorities in England with early-stage heat network work such as heat mapping and feasibility studies. Local authorities were invited to submit zone opportunity areas by 29 May 2026.

See Zone opportunity area, DESNZ, Green Heat Network Fund (GHNF) · Source

A machine that uses electricity to move heat from a cooler place to a warmer one. Air source heat pumps take heat from outside air, water source heat pumps from rivers, lakes or the sea, and ground source heat pumps from boreholes or buried pipes.

See Large-scale heat pump, Ambient loop, Energy centre

An independent, voluntary scheme that sets customer service standards for heat suppliers that register with it. Ofgem regulation of heat networks began on 27 January 2026, so Heat Trust standards now sit alongside statutory rules.

See Ofgem, Citizens Advice, Energy Ombudsman

The Heat Network Technical Assurance Scheme, which will check that heat networks meet minimum technical standards. It has a planned launch in 2027, phased in, and its detail is still proposed.

See Ofgem, Authorisation, CP1 code of practice · Source

The unit on most energy bills. One kWh is the energy used by a 1 kW appliance running for one hour. Heat bills, gas bills and unit rates are usually quoted per kWh.

See Megawatt-hour (MWh), Unit rate, Heat demand

A heat pump big enough to serve a whole heat network from an energy centre, rather than a single building. Common heat sources include rivers, sewers, mine water and outside air.

See Heat pump, Energy centre, Sewer heat recovery, Mine water heat

A unit of energy equal to 1,000 kWh. Annual heat demand for larger buildings is usually quoted in MWh a year, and the proposed zoning threshold for existing non-domestic buildings is 100 MWh a year.

See Kilowatt-hour (kWh), 100 MWh threshold, Heat demand

The Heat Network (Metering and Billing) Regulations 2014 set rules on meters and bills for heat network customers. Amendments from 27 January 2026 removed several requirements, including some notification duties and requirements to fit heat cost allocators and thermostatic radiator valves.

See Heat cost allocator, Ofgem, Unit rate · Source

Heat taken from water in flooded former coal mines, which stays at a fairly steady temperature all year. Heat pumps raise it to a useful temperature for a heat network, which makes it an option in former coalfield areas.

See Large-scale heat pump, Waste heat recovery

The energy regulator for Great Britain. Ofgem became the regulator for heat networks on 27 January 2026, with authorisation conditions applying from that date. Existing networks must register with Ofgem by 26 January 2027.

See Authorisation, HNTAS, Energy Ombudsman · Source

The primary side is the heat network's own pipework, up to the substation or HIU. The secondary side is the building's internal heating system beyond it. Your contract should say clearly who owns and maintains each side.

See Substation, Heat interface unit (HIU), ESCO

The proposed duty to connect inside a zone. It covers new buildings that receive planning permission after designation, existing buildings with communal heating, and existing non-domestic buildings with a wet heating system and average heat demand above 100 MWh a year. Existing individually heated homes are not required to connect.

See 100 MWh threshold, Communal heating, Connection notice, Conditional exemption · Source

Taking heat from wastewater in sewers or at treatment works using heat pumps. Wastewater stays relatively warm all year, which makes it a steady heat source for networks in towns and cities.

See Large-scale heat pump, Waste heat recovery

A fixed daily or annual charge on a heat bill that covers costs that don't depend on how much heat you use, such as maintenance, metering and plant replacement. You pay it even if you use no heat.

See Unit rate, Connection charge, ESCO

The plant in a building where heat passes from the network to the building's own heating system, usually through a plate heat exchanger that keeps the two water circuits separate. It often replaces or sits alongside existing boilers.

See Primary and secondary side, Heat interface unit (HIU), Wet heating system

A delay to connection rather than a release from it. Under the proposals it lasts up to 2 years from the end of the proposed connection window, and you can apply for one during the agreement phase.

See Conditional exemption, Agreement phase, Connection window · Source

A large insulated tank of hot water that holds heat for later. It lets a network run its heat pumps when electricity is cheaper and meet peaks in demand without oversizing the plant.

See Energy centre, Large-scale heat pump

The price per kWh (or MWh) of heat you actually use. A heat bill is usually the unit rate multiplied by your metered use, plus the standing charge.

See Standing charge, Kilowatt-hour (kWh), Metering and billing regulations

A new body created by the Warm Homes Plan. Under the zoning proposals, the Heat Network Zoning Authority sits within DESNZ at first and then moves to the Warm Homes Agency once that is set up.

See Warm Homes Plan, Heat Network Zoning Authority · Source

A government plan published 21 January 2026, including £1bn for heat networks this Parliament. It commits to introducing heat network zoning in 2026 and creates the Warm Homes Agency.

See Warm Homes Agency, DESNZ, Green Heat Network Fund (GHNF) · Source

Capturing heat that would otherwise be thrown away, from industry, data centres, sewers or cooling plant, and feeding it into a heat network, often with a heat pump to raise its temperature.

See Data centre heat, Sewer heat recovery, Energy from waste, Large-scale heat pump

A heating system that moves heat around a building using hot water in pipes, feeding radiators, underfloor loops or air handling coils. Buildings with one are much easier to connect to a heat network, and having one is part of the proposed 100 MWh test for non-domestic buildings.

See 100 MWh threshold, Substation, Flow and return temperatures · Source

The local body that runs a heat network zone, including issuing connection notices. Under the proposals it is set up by local government, and the zoning authority can step in if councils cannot agree within 28 days.

See Heat Network Zoning Authority, Connection notice, Zone developer · Source

The area in which a zone developer would hold exclusive rights to develop a heat network, under the proposals. Exactly how these areas will be drawn depends on regulations that have not yet been made.

See Zone developer, Heat network zone · Source

The formal step that turns an area into a legal heat network zone. No zone has been designated yet, and no zone can be formally designated until the zoning regulations are in force.

See Heat network zone, Zoning regulations, Zone opportunity area · Source

The company that builds and runs the heat network in a zone. Under the proposals it is appointed through competition, with exclusive rights to develop a heat network in the zone delivery area.

See Zone delivery area, Zone coordination body, ESCO · Source

An area that local authorities put forward as a possible future heat network zone. Local authorities were invited to submit zone opportunity areas by 29 May 2026. Submitting one does not designate a zone.

See Zone designation, Heat Networks Delivery Unit (HNDU), Heat Network Zoning Pilot · Source

The proposed maximum penalty for breaching zoning requirements is up to £1 million or 10% of annual turnover, whichever is higher. Fixed penalties are also planned. None of these figures are in regulations yet.

See Requirement to connect, Zoning regulations, Heat Network Zoning Authority · Source

The secondary legislation under the Energy Act 2023 that will switch heat network zoning on. They have not yet been laid before Parliament, so the connection rules, timings, exemptions and penalties in the January 2026 government response are all still proposed.

See Energy Act 2023, Zone designation, Heat network zoning · Source