Megan Coulton, senior associate and Ryan Naidoo, associate in Trowers & Hamlins’ Energy and Sustainability team.
The heat networks sector is undergoing its most significant regulatory transformation in a generation. The Heat Networks (Market Framework) (Great Britain) Regulations 2025, which followed the Energy Act 2023, made heat a regulated utility and introduced an Ofgem-led authorisation regime for heat network operators and suppliers which came into force on 27 January 2026.
Against this backdrop, the Department for Energy Security and Net Zero (DESNZ) has been working with its Technical Author (Fairheat) to develop a technical standards code for heat networks. This code will set out technical requirements (including things like pipe insulation and water flow temperatures) and a scheme of assessment and certification to ensure heat networks comply with and can demonstrate technical compliance. The technical standards (TS1) and assessment/certification procedures form the Heat Network Technical Assurance Scheme (“HNTAS”).
The Government ran a consultation on the HNTAS proposals earlier this year which closed on 15 April 2026. Responses will be published in due course. The expectation is that HNTAS will be phased in over time with a planned launch in 2027.
How will HNTAS apply?
HNTAS will apply to all new and existing heat networks above a certain size. The proposed de-minimus size is a network serving six properties – so it is only the very smallest networks to which HNTAS will not apply. There are also some other proposed exclusions – including for industrial heat networks.
HNTAS will be a performance based scheme which applies to the various elements of a heat network (covering energy centre, distribution network, etc). For each part of the system, assessments against minimum standards will be made. There will be requirements to validate performance standards at design and construction stage and then assessments to verify performance in operation.
New Build Networks
The HNTAS consultation documents set out the proposed ‘pathway’ to design and construct a new build network in compliance with HNTAS, achieve the required certification and then maintain those requirements as part of an ongoing regime.
HNTAS introduces an assurance pathway across four project phases: Feasibility, Design, Construction, and Operation (initial two years). The pathway is structured around four gateways, with assessment defined as a preventative peer review process at key stages, designed to support good outcomes and de-risk certification.
Gateways 1, 2 and 3 are the three critical pre-certification checkpoints, carried out by Assessment Organisations. Certification is issued by an independent third party Certification Organisation. Certificate 1 is issued after commissioning but before customers are supplied heating and hot water and Certificate 2 is issued after 2 years of operation.
Existing Networks
For existing networks, it is acknowledged that existing networks would find it difficult to meet the same standards as New Build networks. On that basis, HNTAS introduces a staged, milestone-based compliance pathway. The pathway involves five Milestones which must be assessed and achieved by specified deadlines. The intention is to allow a significant transition period to allow existing network operators to get the right metering in place in order to be able to prove performance.
Key milestones are:
- Milestone 1 (Year 1): All networks must register with the HNTAS Digital Service. This is separate to the wider Ofgem requirement to register existing heat networks.
- Milestone 2 (Year 3): Post-2015 networks must demonstrate metering and monitoring for the energy centre, substations, network and all end-user connections, alongside threshold performance. Older networks face a proportionately lighter requirement at Year 3, with end-user connection metering deferred to a later milestone. Milestone 2 is primarily focused on reliability and lifespan extension, with water quality, resilience and good O&M practice as key priorities, and the performance threshold is deliberately permissive.
- Milestone 3: For Post 2015 networks, this requires submission of a Performance Improvement Plan (to reach certification) while older networks are also required to complete metering and monitoring all end user connections.
- Milestones 4 and 5 cover the certification stages (which are up to year 10 for older networks (2014 or older)).
Preparing for HNTAS in 2027
One of the key features of HNTAS is that compliance is evidence-based. For developers and landlords entering new-build arrangements, design and technical input must be in line with the draft HNTAS technical standards, build programmes need to allow time for assessment and certification, and building contracts and appointments need to flow down responsibility for compliance with the regime requirements.
Tom Burton, Principal Engineer at Fairheat’s message to developers and operators of heat networks is to get organised early. His top tips to start preparing in time for the 2027 launch are:
New Build
- review existing supplier contracts;
- trial assessments using draft HNTAS documents;
- update internal processes to align with new obligations.
Existing Networks
- review maintenance contracts and processes;
- understand your current portfolio & undertake a gap analysis against proposed Milestone 2 and 4 requirements;
- build a portfolio-based strategy;
- leverage funding to implement improvements;
- prepare for ongoing monitoring requirements.
On funding, Tom notes that the Government’s £5 billion Warm Homes Plan has £3.3 billion still to be allocated, and there is still time to input to the Call for Evidence (open until 1 June) on how those funds will be allocated – including a specific question asking for views on funding to support HNTAS compliance for existing networks.
With compliance with HNTAS set to become a prerequisite for lawful network operation, now is the time to understand the requirements.
Megan Coulton is a senior associate and Ryan Naidoo is an associate in Trowers & Hamlins’ Energy and Sustainability team. With thanks to Tom Burton, Principal Engineer at Fairheat for his valuable contributions.
This article appeared in the June 2026 issue of Energy Manager magazine. Subscribe here.
