PHAM NEWS | JUNE 2026 34 Light CommercialHeating


HIU questions answered


If you come across a Heat Interface Unit (HIU) on site, it might look and deliver heating and hot water like a boiler, but it doesn’t behave the same way. Here, Josh Collins from Altecnic explains the key diff erences installers need to understand.


Units (HIUs) are playing an increasingly important role in modern building services. With the UK’s transition toward low-carbon heating accelerating, and more than 50,000 HIUs installed each year, ensuring these systems perform to a consistently high standard has never been more important. This article explains what a HIU is, how it works, and where it is used, providing a clear overview for those encountering them more frequently in merchants or on site, while highlighting why performance, reliability, and correct specifi cation are key to the success of any heat network.


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What is a heat interface unit? A HIU is a device that connects


individual dwellings to a centralised heat network. Similar in appearance to a standard boiler, a HIU acts as a bridge between the central heat source and hot water outlets within the property, such as radiators, showers, and kitchen taps. Unlike traditional heating systems that require individual boilers in each home, HIUs centralise heat generation, off ering energy and cost savings while providing heating and hot water on demand.


How does a HIU work? HIUs are installed in individual properties, much like a traditional boiler. They are connected to a centralised heat source via insulated pipework. Inside the unit, one or two plate heat exchangers transfer heat from the central system to provide instantaneous heating and hot water as required. Modern HIUs, such as those manufactured by Altecnic, also feature advanced electronic control systems, helping to


s heat networks and district energy systems become more common, Heat Interface


Josh Collins Heat networks manager, Altecnic


improve effi ciency, deliver faster response times, and provide greater overall control.


Where are HIUs used? HIUs are typically found in buildings connected to a heat network, also known as district heating. In these systems, heat is generated centrally - usually within a plant room or energy centre – and distributed as hot water through a network of insulated pipes. These heat networks can be supplied by a variety of central heat sources, including gas boilers, combined heat and power (CHP) units, large-scale heat pumps, and renewable technologies such as


biomass or energy-from-waste systems. As diff erent heat sources operate in diff erent ways, the performance and effi ciency of the HIU at dwelling level becomes increasingly important to ensure reliable heating and hot water delivery throughout the system. This approach is widely


used across multi-dwelling residential buildings, such as apartment blocks, where each property requires its own heating and hot water supply without the need for individual boilers. HIUs act as the link between the central heat source and each dwelling, transferring heat where it is needed while allowing occupants to control their own usage. Beyond residential


developments, HIUs are also used in commercial and public sector buildings, including offi ces, schools, hospitals, and mixed-use developments. Their ability to deliver effi cient, centralised heating makes


them well suited to projects where space, energy effi ciency, and simplifi ed system design are key considerations.


Why is demand growing? HIUs are becoming increasingly popular in modern developments because they simplify heating systems by removing the need for individual boilers in each dwelling. This reduces installation complexity, particularly on larger schemes, while making maintenance easier by concentrating most servicing within a central plant room. They also support low-


carbon heating strategies. Connected to renewable or lower-carbon systems such as heat pumps or CHP, HIUs provide effi cient on-demand heating and hot water while helping reduce emissions. Removing the need for individual fl ues also simplifi es design and improves safety. Within homes, HIUs


free up valuable internal space by eliminating the need for a boiler, while still off ering reliable long-term performance when properly specifi ed and commissioned.


The SATK32 heat interface unit with advanced electronic functions is the


latest ‘intelligent’ range of HIUs from Altecnic off ering a complete solution for instantaneous hot water


production and space heating


What are the benefi ts for occupants? HIUs off er several practical benefi ts for occupants, including instant hot water and responsive heating without the delays associated with stored systems. Their energy- effi cient design can help reduce energy use, lower bills, and cut CO2 emissions. By removing the need for gas


within individual properties, HIUs also improve safety by eliminating the risk of carbon


monoxide. Many systems also include heat meters, giving occupants greater visibility and control over their energy consumption.


What are the diff erences in maintenance? One of the biggest misconceptions on site is that an HIU can be serviced like a boiler because it looks similar and performs the same end function. This diff erence is important for installers and service engineers because faults within an HIU are often caused by wider system conditions elsewhere on the network – not just the unit itself. In reality, servicing an HIU


should be more focused on the following: heat exchanger performance; strainers and fi ltration; pressure diff erential checks; control valve operation; temperature performance; and network- side conditions. ◼ phamnews.co.uk/626/37


LEARNING SUPPORT


 Altecnic Academy offers online HIU training for engineers and installers


 Training covers commissioning, servicing, fault finding, and system operation


 Free hands-on HIU training is available at Altecnic’s Stafford headquarters


 Altecnic supports the Heat Network Maintenance Technician Apprenticeship programme


 Industry bodies provide CPD, technical guidance, and HNTAS and CP1 resources


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