Heat network priority areas and what they oblige
Priority areas are a planning expectation; zoning under the Energy Act 2023 is a duty. The difference decides what evidence a major application has to carry.
A heat network priority area is a mapped zone where the density of heat demand makes a district heating network viable, and where planning policy expects new development to connect to one or be built ready to. In London the concept sits in the London Plan 2021 and the London Heat Map, and heat network priority area planning obligations bite on major development inside those zones. Elsewhere in England the equivalent framework is heat network zoning under the Energy Act 2023, which creates designated zones with real connection duties rather than policy expectations.
The two regimes are often discussed as one thing. They are not, and the difference decides what you have to prove.
What a priority area is and who designates it
A heat network priority area is a planning designation produced from heat demand density mapping. The Greater London Authority identifies them through the London Heat Map, and boroughs reproduce the boundaries in their local plans or policies maps. The logic is linear heat density: a network needs enough demand per metre of pipe to pay for the pipe.
Heat network zones under the Energy Act 2023 work differently. The Act gives the Secretary of State powers to designate zones in England, appoint zone coordinators and require specified buildings within a zone to connect within set timescales. The detail sits in regulations, and the framework was still being implemented when this was written, so check the current position before advising a client that a connection duty applies.
Local plans outside London increasingly carry their own decentralised energy policies with mapped areas. These are policy expectations enforced through the development management process, which means they are weighed in the planning balance rather than imposed as a statutory duty.
The connection expectation inside one
London Plan Policy SI 3 sets a heating hierarchy that major development has to work through in order. Connect to an existing or planned heat network where one is available. Failing that, use a zero-emission or local secondary heat source. Then a low-emission combined heat and power system, and only then ultra-low NOx gas boilers. Within a heat network priority area, the policy also expects a communal low-temperature heating system in major development.
Low temperature matters more than it sounds. A network designed around 70°C flow and radiator-sized emitters cannot later take heat from a large-scale heat pump or waste heat source without replacing the emitters in every flat. Designing the internal system for lower flow temperatures from the start is what keeps the future connection real rather than notional.
The practical consequence for the submission is that the Energy Statement has to record the hierarchy as a sequence of tested options with reasons, not as a conclusion. An energy statement that jumps to air source heat pumps without addressing an adjacent network will come back.
Evidence of an enquiry and a refusal
This is the part that is forgotten and the part that holds up determination. Where a network exists or is planned nearby, the authority will want to see that you asked.
What a usable evidence pack contains:
- A written enquiry to the network operator or the local authority energy team, dated, identifying the site, the expected peak heat load in kW and the annual demand in MWh.
- The operator's written response, including whether capacity exists, the likely connection point, the indicative connection charge and the earliest connection date.
- Where connection is refused or deferred, the reason given in the operator's own words.
- Your assessment of whether the offered terms are deliverable against the development programme.
- A drawn safeguarded route from the site boundary to the likely connection point, with a plant room or energy centre space allocated and sized.
A verbal conversation is not evidence. Nor is an assertion that no network exists, where the heat map shows one under construction two streets away.
Designing for future connection
Where connection is not possible now, the usual outcome is a scheme designed to connect later. That has physical implications which need to be on the drawings at application stage, because retrofitting them is expensive and the condition will require them anyway.
The items that matter are a plant room or energy centre with floor area, floor-to-ceiling height and a route for plant replacement, space for a heat exchanger and thermal store, pipe routes from the site boundary into the building with a capped and valved connection point, a hydraulically separate secondary circuit so the building system can be decoupled, and heat metering at the point of entry and at each dwelling.
Space allocation is the item that gets squeezed between planning and construction. A plant room shown at 18m² on the planning drawings and delivered at 11m² after the structural grid moves cannot take a heat exchanger set. Dimension it, and say in the Sustainability Statement what the allocation is for.
Metering strategy is a related decision with consequences for billing, regulation and the eventual network operator's requirements. Metering and submetering strategies for mixed use goes into how that is set out.
Zoning powers and how they change the picture
The Energy Act 2023 framework moves heat networks from a policy expectation to a regulated market. Heat networks became a regulated sector with a designated regulator, consumer protection rules and authorisation requirements. Zoning adds the ability to require certain buildings inside a designated zone to connect.
For a developer, the practical questions are whether the site falls inside a designated zone, whether the building type is one the regulations capture, and what the compliance deadline is. Where the answer to the first is yes, a scheme designed only to connect at some future date may not satisfy the duty.
Because the start dates and the detail of the regulations are the moving parts here, treat any statement about connection duties as something to verify on gov.uk at the time you advise. The direction is settled. The dates are not.
Conditions and obligations used
Three mechanisms turn up on decision notices inside priority areas.
A condition requiring the heating system to be installed in accordance with an approved energy strategy, with the safeguarded plant space and connection point provided before first occupation. This is the most common and the easiest to discharge.
A condition requiring a connection agreement to be entered into before occupation where a network is available. Read this one carefully, because it makes occupation dependent on a third party's commercial decision.
A section 106 obligation to connect within a stated period of a network becoming available within a stated distance of the site, sometimes with a financial contribution towards network extension. The drafting points to argue are the distance trigger, the definition of availability, the reasonableness of the connection cost and whether the obligation binds successors in title indefinitely.
Ask for a cost cap. An unqualified obligation to connect at whatever the future charge happens to be is an open-ended liability on the land.
Checking whether a site is inside one
Start with the London Heat Map for London sites, then the borough's policies map, then the local plan text, because the map and the policy can be updated at different times. Outside London, check the local plan and any supplementary planning document on energy, then the authority's own climate or energy strategy, which often names networks before the plan does.
Also check the practical facts. An existing network with a connection point 400 metres away and spare capacity is a very different proposition from a zone designated on demand density with no network built. The heat map shows both, and the distinction should be stated plainly in the energy statement rather than blurred.
Grid capacity is the sibling constraint, since a scheme that cannot connect to a heat network and cannot get an electrical supply upgrade has nowhere left to go. Grid connection capacity as a planning constraint covers how that is evidenced.
PlanScope can draft an Energy Statement structured to the heating hierarchy, with the network enquiry evidence and the safeguarding commitments set out and any missing site facts flagged. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Energy and heat network design is engineering work, so treat a draft as the starting point for a qualified designer. This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
What is a heat network priority area?
A mapped area where heat demand density is high enough to make a district heating network viable. In London the Greater London Authority identifies them through the London Heat Map and boroughs reproduce the boundaries in local plans. Inside one, London Plan Policy SI 3 expects major development to connect to a network or to be designed so it can connect later.
Is connecting to a heat network compulsory?
Inside a priority area it is a policy expectation weighed in the planning balance, not a statutory duty. Heat network zoning under the Energy Act 2023 is different, because it allows specified buildings inside a designated zone to be required to connect within set timescales. The detail sits in regulations, so check the current position.
What evidence does the council want about a possible connection?
A dated written enquiry to the network operator giving the peak heat load and annual demand, the operator's written reply on capacity, connection point, indicative charge and earliest date, and the reason for any refusal. A verbal conversation will not do, and neither will an assertion that no network exists where the heat map shows one nearby.
What does designing for future connection actually involve?
A dimensioned plant room or energy centre with space for a heat exchanger and thermal store, a safeguarded pipe route from the site boundary with a capped and valved connection point, a hydraulically separate secondary circuit, heat metering at entry and per dwelling, and emitters sized for low flow temperatures so the system can later take lower temperature heat.
What should I check in a section 106 connection obligation?
The distance that triggers it, how availability is defined, whether the connection cost is capped, how long the obligation lasts and whether it binds successors in title. An unqualified duty to connect at whatever the charge turns out to be leaves an open-ended liability on the land, so a cost cap is worth negotiating before signing.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.