Technical Standard For UK HIU Test Regime 3.1 (Update 2026)

Setting the Performance Standard for Heat Interface Units (HIUs)

With over 50,000 Heat Interface Units installed annually in the UK, establishing clear performance standards is essential to improving the efficiency of heat networks and supporting the UK’s net zero strategy. This third edition of the BESA Test Standard introduces a modular testing framework that reflects the latest advancements in technology, operating practices, and low-carbon network development.

Developed with the backing of the Department for Energy Security and Net Zero (DESNZ) and shaped by a cross-sector industry steering group, the UK HIU Test Standard provides impartial, detailed performance assessments. It enables designers, specifiers, operators, and developers to make informed, consistent decisions for both new-build and existing residential heat networks.

Key Updates In Version 3.1 Include:

• Updates on revised pass thresholds and best‑practice values.

• changes aim to support the mission of improving the performance of residential HIUs across the UK.

• New pass/fail criteria have been added for:

Indirect space heating average temperature

Indirect space heating mix‑down temperature stability

• A detailed changelog will be included to help users understand all adjustments.

• With the forthcoming release of HNTAS, which requires HIUs to pass the BESA HIU Test Regime (or equivalent), these updates will help ensure better outcomes for consumers.

• With the release of Version 3.1, the results of all tests to the 2018 (Version 2) of the test standard will be moved to an archive version on the website and will no longer be registered

The HIU Test Standard has already had a measurable impact in reducing carbon emissions, improving heat network service quality, and driving innovation through consumer-led market transformation.

Also available to download are the individual BESA HIU Test Modules from 1 to 10.