YGHP Indirect Heat Interface Unit

‘The most cost effective, high performance indirect heat interface unit on the market today’. 


DHW: 45kW

HTG: 15kW



You have selected a high-quality Heat Interface Unit (HIU) for your heating and domestic hot water (DHW) needs.

The HIU should be used exclusively for radiator/floor heating and DHW preparation.

YGHPs Heating Interface Unit (HIU) product range is designed to satisfy a wide variety of customer demands in terms of heating and domestic hot water (DHW).

The HIU provides complete solutions for apartments and houses to make radiator heating or underfloor heating

and instantaneous DHW preparation with thermostatic control.

The HIU Indirect is specifically designed for  radiator / floor heating and instantaneous DHW
preparation with thermostatic control.

It has all the necessary components (e.g. valves, heat exchangers (DHW heat exchanger and heating circuit heat exchanger), pump, expansion vessel, pipes, fitting and
connections) to deliver convenient and efficient DHW and heating.

Optional components such as the re-circulation component enables the HIU to deliver instantaneous DHW, the hot water priority component switches the HIU to
prioritise the DHW supply, and the Thermostatic Actuator enables the HIU floor to open or close the heating circuit remotely.

The HIU indirect has 3 types based on the number of plates of its DHW heat exchanger: 30, 40, or 70 plates.

To connect the HIU indirect with the piping system of apartments or houses, mounting plates with 8 Ball valves are used. The flushing bypass component enables flushing and venting the system before commissioning.

The HIU indirect is covered with a high quality thermal EPP Cover.

2.Design and Technical Description of the HIU and Its Components

The HIU indirect is comprised of 14 main components. The components of the HIU are secured on a galvanized steel plate.

Each has a DHW brazed plate heat exchanger (optionally isolated with EPP), thermostatic control valve, differential pressure control valve, heating component,

air vent, water hammer, spacer for heat meter.

The 18 mm diameter pipes of the HIU are made from AIS 316L stainless steel .

Figure 2 describes the inlets and outlets of the HIU indirect. Figure 3 shows the dimensions of the HIU indirect.

The technical data of the HIU indirect on the general aspects, materials, dimensions, heating circuit, domestic hot water, and electrical connections are presented in Table 2.

Table 2. The technical data of the HIU indirect



Each HIU indirect is equipped with a differential pressure control valve (Figure 4) which balances the system to react to pressure variations in variable flow systems.

In hydronic heating systems with a HIU, differential pressure control valve prevents any high pressure difference on the HIU

by providing the necessary conditions to achieve the desired flow distribution within the system.

The differential pressure control valve balances all components of the HIU system.

In the HIU, differential pressure control valves with sizes of DN20, Kvs of 2.5 m3/h, ΔP Setting range of 20-65 kPa, and Nominal Pipe Size of ¾” are used.

The technical specifications of the pressure control valve are given in Table 3.



Each HIU indirect is equipped with a DHW brazed plate heat exchanger (Figure 5) to transfer heat from the heating supply to the HIU for DHW preparation.

In the HIU indirect, the DHW heat exchanger has optimized asymmetric plate geometries that combine extraordinary thermal efficiency with a low pressure drop and
low return temperatures.

The performance data of the DHW heat exchanger is given in figure 7.


The DHW thermostatic control valve (Figure 9) is a simple yet reliable device for accurate temperature control that works without power supply and active control.

These valves can ensure virtually constant temperatures. The thermostatic control valves are optimized for minimal idle consumption and maximum stability.


The HIU indirect is designed in such a way that it can provide either radiator or floor heating with a thermostatic valve range change. If radiator heating is preferred, the radiator heating component would enable radiator heating functionality with a range of 40-90 °C.

Alternatively, if floor heating is preferred, the floor heating component would enable floor heating functionality with a range of 20-70 °C.

Each Heating Component has a heating brazed plate heat exchanger, safety valve, combined thermometer/pressure gauge, expansion vessel, electronically-controlled circulation pump, heating thermostatic control valve, 18 mm AIS316L stainless steel pipes with 9 mm isolation, and brass fittings and connections.


The Safety Valve (Figure 10) serves as a fail-safe to protect against over pressure in the HIU.

When the system pressure of the HIU exceeds 2.5 bar (factory adjusted opening pressure), it automatically releases water from the draining outlet.

The system pressure of the HIU can be monitored by the combined thermometer/pressure gauge.

The safety valve is made from brass and according to the standards established by DIN 4751-3 and EN 12828 regulations.

The technical specifications of the safety valve are provided in the Table 5.



The combined thermometer/pressure gauge enables the operator to observe the heating circuit temperature and system pressure in a single gauge at a single measuring point.

It has a bimetal measuring system for temperature measurement and a bourdon tube measuring system for simultaneous pressure measurement.

Both values are measured and displayed by a single gauge.

A self-closing mounting valve enables the gauge to be replaced without the need to drain the system.

The technical specifications of the combined thermometer/pressure gauge are provided in Table 6.



Each floor heating component has an electronically-controlled circulation pump (DN 15 size and 7 mm hydraulic performance) which is exclusively designed for circulating heating systems with constantly changing volume flows.

The technical data of the pump is presented in Table 8. In Figure 13, the pump curve (pump head vs flow rate characteristics) is given.


The HIU indirect comes with a filling (Figure 14) component which is used to fill the heating circuit with water.

It should be manually connected to the ball valves of the HIU (marked with “A” and “B” stickers) to start the filling process.

The heating circuit should be filled with water until 1.5-2.0 bar pressure read from the combined thermometer/pressure gauge.

Then, those ball valves should be shut-off, and the filling component should be disconnected from the HIU.

It is made up of AIS 316L stainless steel pipes with union nuts at both ends.

The filling component is marked with “A” and “B” stickers at the ends to correctly connect to the HIU.


The thermostatic actuator (Figure 15) enables the HIU to open or close the heating circuit remotely.

It receives electrical signals from room or timer thermostats or other home automation systems and convert those electrical signals into valve strokes to adjust the on or off condition of heating circuit.

The technical specifications of the thermostatic actuator are provided in the Table 9.

The thermostatic actuator is an optional component in the HIU indirect design.



The YGHP Indirect HIU is the perfect heat interface unit to offer stable yet high performance.