Heat Interface Units (HIUs), also known as Thermal Interface Units (TIUs), are used to efficiently distribute heat and hot water to district heating or network heating projects. HIUs are similar in appearance to a standard boiler and are typically used in heat networks. Heat networks are systems that use a centralised heat source (usually located in a plant/mechanical/boiler room) to distribute hot water through a network of insulated pipes. This system is generally used to fulfil heating and hot water requirements in residential buildings such as apartment complexes but is also used in educational and commercial buildings.

HIUs are installed into each property in the building as a boiler would be. The unit is connected to one central boiler through a network of pipes. HIUs incorporate one or two-plate heat exchangers to transfer the heat from the central system into instantaneous heating and hot water as and when it is required. HIUs incorporate an internal electronic control unit that ensures maximum efficiency, improved reaction time and control, but also incorporates other additional features. Modulating valves control the supply of hot water to both the space heating and domestic hot water within the apartment. The thermally insulated casings also minimise heat loss from the unit.