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Why HIU testing to BESA 3.0 and 3.1 matters
as heat networks move toward regulation The UK heat network sector is entering a signifi cant period of transition. What was once largely driven by best practice, voluntary standards and performance-led specifi cation is rapidly moving toward formal technical regulation. For manufacturers, contractors, developers and building owners alike, this changes the conversation around Heat Interface Units (HIUs), as Steve McConnell, director of ICOM and MEHNA, explains
H
IU performance is no longer simply a matter of product effi ciency or consumer satisfaction. It is increasingly becoming a
regulatory compliance issue. With the introduction of the Heat Network
Technical Assurance Scheme (HNTAS), independently verifi ed HIU performance will play a central role in demonstrating compliance with future technical standards. This makes understanding the latest BESA HIU testing standards, particularly Versions 3.0 and 3.1, essential for everyone involved in the design, installation, specifi cation and operation of heat networks.
A new regulatory era for heat networks
The Energy Act 2023 established the framework for introducing mandatory technical regulation across UK heat networks. This is a major step forward for the sector and refl ects the growing importance of heat networks in delivering low-carbon heating at scale. To support this transition, HNTAS is being developed as the framework for assessing and certifying compliance with future technical requirements. Government guidance from DESNZ has confi rmed that HNTAS will be introduced in phases, with implementation expected to begin in 2027. This phased approach is designed to give the industry time to prepare, adapt and demonstrate compliance. However, preparation should already be
underway. Milestone 1 readiness is not something that can be left until the fi nal stages. Heat network owners, operators, developers, designers and suppliers should be reviewing equipment specifi cations, operational records, monitoring arrangements and performance evidence now. The businesses that act early will be far better positioned to avoid future compliance challenges.
Why BESA HIU testing matters more than ever
BESA testing has long provided an independent and recognised method for assessing HIU performance. It gives specifi ers, developers and network operators confi dence that products have been tested under impartial and consistent conditions. That independent verifi cation is becoming increasingly valuable. As technical regulation develops, stakeholders
10 August 2026
Left: Steve McConnell, director, ICOM
are looking beyond marketing claims and manufacturer datasheets. They want robust, independently verifi ed performance data that supports informed specifi cation decisions and contributes to improved network performance. This is exactly where BESA testing provides value. Verifi ed HIU performance data supports: ¡ Better product selection ¡ Improved network effi ciency ¡ Lower operating costs ¡ More consistent consumer outcomes ¡ Stronger compliance evidence In short, better testing leads to better-performing heat networks.
The signifi cance of BESA Version 3.1
The release of BESA Test Standard Version 3.1 represents an important evolution in HIU testing, not just an administrative update. Version 3.1 raises the benchmark for performance and introduces more rigorous assessment criteria.
One of the most signifi cant changes is the inclusion of additional pass/fail criteria for indirect space heating performance. This includes temperature stability requirements, which are particularly important for ensuring reliable system operation and consumer comfort. These changes matter because temperature stability has a direct impact on both network effi ciency and end-user experience. Poorly controlled heating performance can result in ineffi ciencies, higher energy consumption and dissatisfi ed residents. By strengthening these requirements, Version 3.1 helps drive higher- performing HIUs and better overall heat network outcomes. Version 3.1 is now the most up-to-date BESA
HIU Test Standard and should be regarded as the current benchmark for UK heat network projects. Version 3.0 remains valid and continues to provide recognised evidence of independently verifi ed HIU performance. However, earlier Version 2 testing results will be withdrawn from the active BESA register, and that transition carries important implications for manufacturers and specifi ers.
Older test results should not be assumed valid
This is a critical message for the industry. Manufacturers should not assume that historic BESA test reports will remain suffi cient. As Version 3.1 becomes the recognised standard,
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