After Sales After Sales ContactsContacts 0845 241 1441
Thermal Integration Ltd

Heat Interface Units

Heat Interface Units

Heat Interface UnitsHIUs (heat interface units) provide domestic hot water and central heating in properties connected to a district heating system using a central boiler.

For some years, there has been an increasing use of centralised boiler plants in property developments. The advantages of removing gas boilers from properties and making use of high efficiency centralised boiler plants are numerous.

Advancing technologies such as Combined Heat and Power (CHP), Biomass, Extract Air Heat Pumps, Waste Incineration, and Solar, that are mostly uneconomical to employ in individual properties, can be utilised and combined to generate heat to numerous properties. Heat Interface Units, or HIUs for simplicity, are fitted into each property and take the heat from the central plant, and use this to provide central heating and hot water to taps. It is easiest to think of an HIU as a combination boiler, running off heat from pipes rather than a gas supply. Occupants are charged for units of heat, rather than units of gas, and typically come with heat meters to measure energy use.

Solving the Problem

Probably the biggest problem with HIUs, and district heating in general, is the heat loss. In order to ensure that hot water is available without delay, all HIUs draw a trickle flow of hot water from the primary supply to overcome heat losses, and in nearly all cases this runs continuously.

The implications of this continuous heat loss is most keenly felt in properties fitted with pre-pay systems, where the user can find their remaining credit drain away needlessly, when the property is unoccupied.

The designers at Thermal Integration have focused a great deal of effort ensuring every possible step is taken to solve this key problem.

Moulded EPP Insulation

One way to reduce the rate of heat loss, is to insulate. The range of Thermal Integration HIUs make use of highly engineered EPP (Expanded Polypropylene) moulded enclosures that encase individual components supporting assemblies and preventing any heat bridging to the environment. Heat losses of under 2W are available, making the drain on energy use less than 1 pence per day.

Economy Mode

Another way to reduce losses is to allow the system to go cold when not in use. The range of electronic HIUs provide an optional Economy Mode whereby the Hip will go cold after one hour of inactivity significantly reducing energy consumption furthers Sterilisation cycles ensure that the system is never left cold for extended periods, to prevent a build-up of Legionella bacteria.

Advanced Heat Exchange

The final way to reduce heat losses, on the district system as a whole, is to run the network at lower temperatures, typically 65C flow and 35C return, with very low temperature drop across the plates. Multi-pass heat exchangers are used to ensure these types of temperature drops can be achieved, while maintaining turbulent flow across the range of outputs.


To simplify the process of securing bolts and access points on HIUs, we make use of unique moulded security clips and caps that once assembled, makes it impossible to access a bolt head or connection nut without breaking the cap.

To secure casings, and any bolted on components that one would like secured, we use a Bolt Security Cap.

Bolts are inserted through the lower part of the security cap assembly, and screwed into position. The upper part is then pushed into the lower part until it locks, at which point the cap cannot be removed, and the screw head cannot be accessed.

Components such as heat meters and security valves require security measures to be fitted to the pipework connections, to prevent their removal from the system without trace. The Meter Security Clips come in various sizes and provide a permanent security fixing that prevents access to connections without breaking the seal permanently.

Heat Interface Units