How BESA’s HIU Test Regime is shaping the future of UK heat networks

Josh Collins at Altecnic explores how heat networks are being shaped by BESA’s HIU Test Regime.

Over 50,000 heat interface units (HIUs) are installed each year in the UK, and ensuring these devices perform to a consistently high standard has never been more urgent. Poorly performing HIUs can impact the overall health of a heat network which will subsequently lead to higher energy cost for the consumer.

This is why the BESA HIU Test Regime is so important. First supported by government-funded research in 2016, and later developed by the Building Engineering Services Association (BESA) in 2018 and 2023, the regime has changed how HIUs are assessed. What was once an unclear, manufacturer-led process is now a transparent, independent benchmark focused on real performance.

Today, the BESA regime is widely recognised across the industry. It is referenced in CIBSE CP1 (2020) and is becoming increasingly important as Ofgem prepares to regulate heat networks through the Heat Network Technical Assurance Scheme (HNTAS).

From voluntary scheme to industry benchmark

What sets the BESA HIU Test Regime apart is its consumer-first approach. Operated as a not-for-profit scheme, it is independent of individual manufacturers and designed to protect network performance as a whole. The regime provides:

• Realistic testing scenarios under both high and low-temperature conditions.
• Replicable results across approved test houses.
• Pass/fail thresholds to prevent poor performance slipping into the market.
• Best practice criteria, which set aspirational goals for manufacturers to target.

The 2023 update significantly expanded the scope of testing. It introduced modular assessments for space heating and hot water, tightened performance thresholds, and placed greater emphasis on return temperatures using Volume-Weighted Average Return Temperature (VWART). It also added standby energy measurements and updated hot water response time requirements.

Together, these changes ensure HIUs are assessed not just on comfort and speed, but on how well they support low-carbon, real-world heat networks.

This dual structure is key. Pass/fail criteria ensure minimum consumer expectations are met, while best practice benchmarks give designers and developers a clear signal: higher-performing HIUs lead to more efficient, future-ready networks.

Altecnic’s SATK32107: Best practice example

In the latest BESA test regime (V3-Rev001, 2023), the SATK32107 HIU passed all four indirect test modules and achieved multiple best practice results.

The test results highlight:

• DHW response times of 9 seconds (70°C) and 15 seconds (55°C) – within the 15-second limit, with best practice achieved under high-temperature operation.
• Standby energy losses of just 0.939–0.945 kWh/day, comfortably below the 1.0 kWh/day compliance threshold.
• VWARTs as low as 27°C (high-temperature) and 30°C (low-temperature), supporting low-return, heat-pump-ready networks.
• Proven compliance across all modules (1, 2, 7 & 8) with no fail criteria triggered.

These results confirm the SATK32107 is not only compliant but futureproofed for the UK’s next generation of heat networks, where low return temperatures and efficient standby management are essential.

Why does this matter?

As we move through 2026 and beyond, the significance of the BESA HIU Test Regime grows even further. Heat networks are no longer a niche solution; they are central to the UK’s decarbonisation strategy, expected to supply nearly a fifth of homes by 2050.

• For consultants and developers, transparent test data allows the design of networks that are heat pump-ready (low temperature) and scalable for the decades ahead. Instead of relying on theoretical performance claims, designs can be grounded in real, replicable results.
• For operators, reliable HIUs mean networks that can deliver consistent comfort while adapting to seasonal and long-term changes in demand. As DESNZ Heat Network Technical Assurance Scheme (HNTAS) begins to bite, the ability to evidence compliance through BESA testing will become a regulatory necessity.
• For end-users, this translates into fair bills, faster hot water, and confidence that their heating is not only reliable but aligned with the UK’s climate ambitions.

At the system level, this matters most. Lower return temperatures, reduced standby losses, and proven hot water response times are not just performance metrics, they are enablers of the low-carbon transition. They allow networks to integrate large-scale heat pumps, make better use of waste heat, and operate at the lower flow temperatures essential for efficiency. In short, the HIUs being tested today are laying the foundation for the heat networks of tomorrow, and by extension, for the UK’s ability to meet its net zero targets.

Raising standards beyond 2026

The BESA HIU Test Regime is reshaping the sector. By enforcing strict pass/fail criteria, it prevents underperforming HIUs from damaging network performance. By setting clear best practice benchmarks, it pushes manufacturers to innovate rather than simply comply.

This approach is already delivering results:

• Lower return temperatures and higher network efficiency
• Reduced standby energy use, cutting costs and emissions
• Faster hot water delivery and improved user experience
• Better flow rate control at low heating outputs.

As regulation tightens and heat networks expand, the BESA regime is becoming a driver of continuous improvement. Looking ahead to 2030, the industry is likely to see this period as the point when HIU performance shifted from inconsistent and opaque to standardised and transparent.

Altecnic’s SATK32107 is an example of what that trajectory looks like in practice: a unit that not only passes every compliance test but performs strongly against best practice. The bigger impact of this can be seen across the market, with independently validated excellence setting the baseline for what networks, regulators, and consumers expect.

Conclusion

As the UK accelerates its transition to low-carbon heat, the performance of HIUs will be under sharper focus than ever. The updated BESA HIU Test Regime has provided the sector with what it lacked for so long, a transparent, independent, and rigorous framework that separates proven performance from marketing promise. It has set a baseline for compliance, while also pointing towards best practice that challenges manufacturers to innovate.

For consultants, developers, and operators, the value is clear: reliable data to inform design, specification, and long-term operation. For end-users, it means networks can deliver what they promise, efficient systems, lower costs, and fast, dependable hot water. And at the system level, it ensures that networks are not just functional today, but ready to integrate the low-carbon technologies essential for tomorrow.