Direct FlatStation HIUs

One of the most popular models of direct HIUs is the FlatStation 5 Series.

In this, the central plant primary flow and return connect directly to apartment space heating circuits, without an intermediate exchanger. This arrangement usually serves radiator circuits, but can be adapted to accommodate underfloor heating (UFH).

Hot water and heating to each apartment are both provided by means of a wall mounted heat interface unit. The FlatStation 5 HIU Series can serve up to 7 flats in a block. Room temperature is controlled via a thermostatic controller on the primary return. Good authority and steady operation by this valve is ensured by a pressure regulating valve placed across the flow and return connections. Mechanical design of FlatStations is extremely compact, even when energy meters are specified. Covers can be specified with a choice of finish to meet aesthetic requirements.

Hot water heaters

Each Series 5 FlatStation includes an instantaneous hot water heater for the incoming mains cold water. Heat is provided by a plate heat exchanger, fed by the community heating system.

There is automatic thermostatic control of hot water temperature at the taps, enabling a constant, reliable hot water supply temperature at all times. Outlet temperature is kept steady, regardless of pressure or temperature variations in the community heating system or cold water supply.

To ensure that demands for hot water are met at the required temperature, a thermostatically controlled bypass maintains a trickle flow just upstream of the taps.

Central heating circuits

Water for central heating systems flows directly through the heat interface unit. This part of the circuit includes the following features:

  • A strainer in the primary pipework to protects the primary side of the plate heat exchanger from circulating debris.
  • A differential pressure control valve in the primary side pipework to maintains a constant pressure differential across the heating circuit, regardless of variations in pump speed or valve closures in other parts of the community heating system. This is protected by a strainer in the return line.
  • A 2- port on/off control valve on the return side of the primary pipework prevents energy losses when heating is not required.
  • An energy meter in the primary side pipework monitors the energy consumption by each apartment. The measurement accuracy of the energy meter is compliant with the requirements of EN 1434 (MID) class 2.
  • A strainer in the return side pipework to protect the control valves.

HIU Installation

Heat interface units are supplied with ball valves in all pipework connections to and from the units, so that isolation can be carried out simply and effectively.
To ensure that pressure differentials between primary flow and return can be easily verified, pressure gauge tappings are provided on the HIU side of the ball isolators.
To help with system cleaning, a fixed full-bore bypass is strongly recommended to allow flushing of the system pipework without having to circulate flushing water through the heat interface unit. Commissioning engineers find this facility especially valuable.
Pipework to heat interface units is offered with all connections made to the top, bottom, or a mixture of the two.


For further information about Danfoss FlatStations or Pt40/Rt40 valves, please contact us:

By phone: 01483 771910
By e-mail:

We look forward to hearing from you!

Document Downloads

Please click on the thumbnails below to download the relevant document.

FlatStation Specifications

FlatStation 1 Series Specification

FlatStation 1 Series Specification

FlatStation 5 Series Specification

FlatStation 5 Series Specification

FlatStation 7 Series Specification

FlatStation 7 Series Specification

FlatStation Prepayment Specification

FlatStation Prepayment Valve
& Actuator Specification

Pt40 & Rt40 Specifications / Order Sheets

Pt40 Specification Document

Pt40 Specification Sheet
(Microsoft Word)

Pt40 Specification Document

Rt40 Specification Sheet
(Microsoft Word)

Pt40 Selection and Ordering Sheet (Heat Networks)

Pt40 Selection and Ordering Sheet (Commercial)

Rt40 Selection and Ordering Sheet

Design Guides / Technical Datasheets

For access to the documents shown below please fill out and submit the form.

FlatStation Design Guide

FlatStation Design & Product Guide
(Rev 8)

Delta T Design Guide

Delta T Design Guide
(Rev 2)

Pt40 Product Overview

Pt40 Technical Datasheet

Rt40 Technical Datasheet

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