Heating Interface Units (HIU)

The UK’s Test Regime for Heat Interface Units has been developed to assess the UK’s heat network operating parameters. It is an important step to raise the performance standard of the HIU market and improve the overall performance of UK's district heating schemes.

FOR HEAT CUSTOMERS - Designed with the consumer in mind, BESA’s Test Regime ensures the HIU market meets the needs of those developing and designing heat networks that ultimately benefits the consumer.

FOR MANUFACTURERS - The Test Regime is voluntary but it provides you with a pragmatic and practical way to test, assess and compare the performance of your HIUs.

HIU’s can be published & registered with BESA without regulatory approval (WRAS/KIWA) if evidence is provided that submission for this approval has been undertaken. If approval has not been issued within 12 months of publishing, this will be reviewed.

New Technical Standard for UK HIU Test Regime now available 

The new HIU test standard is now available to download for free and will supersede the standard created in 2018. Test results from the 2016 standard will be removed 3 months from the release of the new standard. To read more please visit the documents and downloads page.


  • To enable the performance of different HIUs to be evaluated within the context of typical UK operating conditions thereby enabling heat network developers to evaluate the performance of specific HIUs against design requirements
  • To generate operating data on the expected performance of specific HIUs given "normal" operating parameters to enable heat network operators to identify anomalous performance 
  • To provide a framework for HIU manufacturers to evaluate the performance of their equipment within the UK context thereby feeding into their continuous improvement development programmes 


  • Mapping of key metrics over the duration of each test
  • Calculation of the annual Volume Weighted Return Temperature (VWART) from the HIU, with this being a composite of estimations of the annual volume-weighted return temperatures for domestic hot water, space heating and keep-warm functions 
  • Evidence of compliance with other performance and reliability metrics, such as speed of temperature stabilisation.