The development of new heat networks supported by the Green Heat Network Fund (GHNF), and the improvement of existing ones through the Heat Network Efficiency Scheme (HNES), form an important part of the government’s plan to reduce carbon and cut heating bills for customers. But as the UK heat network market evolves, there has been increasing discussion – and, in some cases, misunderstanding – around one particular aspect of a heat network system: the possible future requirements for testing and verification of the Heat Interface Unit (HIU).
The confusion concerns the BESA HIU Test Regime and the proposed Heat Network Technical Assurance Scheme (HNTAS). A range of claims is circulating about what is and is not required today. So, this article aims to clearly set out the current position of HIU requirements and look at what lies ahead from what we know so far, without speculation.
Authored by Senior Product Manager, Charlie Mowbray, this article cuts through speculation to provide clarity, confidence and a clear roadmap for the future.
What is mandatory today?
At present, there is no legislative or mandatory requirement for a HIU manufacturer to supply a BESA-tested appliance. There is also no legal obligation for a HIU to have been tested to the BESA 2023 regime, or any previous or subsequent updates.
Where manufacturers have chosen to undertake BESA testing, both the 2018 and 2023 test regimes have, until recently, been recognised by BESA. Importantly, even appliances that have not been tested under either regime remain fully permissible for use in heat networks at the present time.
Ideal Commercial Heating’s current POD HIU range was tested to the 2018 BESA test regime, which at the time was the recognised industry benchmark. Today, POD HIUs remain fully compliant with all mandatory market and regulatory requirements, necessary to be CE marked and UK Water Regulation 4 approved and continue to be specified and installed across UK heat network projects.
BESA testing: evolving, but still optional
BESA is proposing further changes to the current 2023 test regime, with a potential new iteration expected shortly. While the original publication date was proposed for the end of 2025, the final version is still to be published, expected February 2026.
When a new version is introduced, BESA has indicated that results from earlier regimes will no longer be recognised by the organisation. However, even in that scenario, it is critical to understand that BESA testing itself would still not be mandatory unless required under legislation.
Currently, only a limited number of manufacturers appear on the published BESA 2023 test list, with others expected to follow. The changing position on recognition of previous test regimes has added to confusion in the market, particularly for manufacturers and developers with projects already in planning or delivery.
HNTAS: intention versus reality
The Heat Network Technical Assurance Scheme (HNTAS) is a government-backed initiative intended to provide a framework to guide the design and implementation of heat networks and regulation by OFGEM to protect homeowners from high energy costs and poor system performance – challenges that have historically affected some heat networks.
HNTAS references BESA HIU testing as a means of demonstrating appliance efficiency. However, HNTAS itself is still in development. There is currently:
- No published final draft for consultation
- No finalised technical requirements
- No enacted legislation to support enforcement
Based on industry engagement to date, it is our opinion that the earliest realistic timeframe for HNTAS introduction is 12–18 months away (so not until 2027), subject to successful consultation.
When introduced, HNTAS is expected to apply to new and existing heat networks, although the definition of what constitutes “existing” has not yet been made public. As with previous regulatory changes, such as the introduction of Building Regulations Part L 2022, a period of derogation would be expected, between publication and impact.
Ideal’s position: clarity, compliance and a clear roadmap
Ideal Commercial Heating is actively reviewing all documentation, testing regimes and proposed legislation relating to heat networks and HIUs.
Our position is straightforward:
- We support the ambition of HNTAS to provide protection to heat network customers
- POD HIUs are currently compliant and can be specified with confidence
- There is no current regulation restricting HIU use based on BESA test status
- Both tested and untested appliances are currently permitted in the market
At the same time, we recognise that the BESA test regime is evolving and that future legislation under HNTAS is likely to change expectations for HIU performance. When regulation is finally introduced, our products will be designed to meet it fully and effectively, rather than reacting prematurely to standards that are still in flux.
Confidence through transition
The heat network sector is at a pivotal point. Clear information, proportionate regulation which provides positive benefits and protections for consumers, and realistic timelines are essential to enable continued investment, and to allow us to contribute to the continued success of the heat network sector.
Ideal Commercial Heating remains committed to supporting the market with compliant, reliable and installer-friendly HIUs today – and with future-ready solutions in line with the regulatory landscape.
Until then, clarity matters. And the facts are clear: POD HIU is compliant, proven and ready now, with a responsible evolution planned for the future.
Date: January 2026