Rehau STAR 20 Instruction sheet

Building Solutions
Automotive
Industry
REHAU STAR CONTROLS
INSTALLATION GUIDELINES
www.rehau.co.uk
Valid from May 2011
Subject to technical alterations

3
REHAU STAR CONTROLS
CONTENTS
1 . . . . . . . . Explanation of Symbols . . . . . . . . . . . . . . . . . . . . . . 04
2 . . . . . . . . Safety Instructions . . . . . . . . . . . . . . . . . . . . . . . . 05
3 . . . . . . . . REHAU STAR Controls . . . . . . . . . . . . . . . . . . . . . . . 06
3.1 . . . . . . . The STAR Controls Range . . . . . . . . . . . . . . . . . . . . . . 07
3.2 . . . . . . . For the Installer . . . . . . . . . . . . . . . . . . . . . . . . . . 08
3.3 . . . . . . . For the Homeowner . . . . . . . . . . . . . . . . . . . . . . . . 09
4 . . . . . . . . REHAU STAR Technical Data. . . . . . . . . . . . . . . . . . . . . 10
4.1 . . . . . . . STAR 20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2 . . . . . . . STAR 30 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.3 . . . . . . . STAR 50 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.4 . . . . . . . STAR Pump Relay . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.5 . . . . . . . STAR Centre . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5 . . . . . . . . Overview of Main Features . . . . . . . . . . . . . . . . . . . . . 15
6 . . . . . . . . General Underfloor Heating Guide . . . . . . . . . . . . . . . . . . 17
7 . . . . . . . . Principles of Controlling an Underfloor Heating System (UFH) . . . . . . . 19
8 . . . . . . . . REHAU STAR Controls Installation . . . . . . . . . . . . . . . . . .22
8.1 . . . . . . . Electrical Installation . . . . . . . . . . . . . . . . . . . . . . . . 23
8.2 . . . . . . . STAR Centre and STAR Pump Relay Connection and Mounting . . . . . . . . . 24
8.3 . . . . . . . Installer/User Setup STAR 50 . . . . . . . . . . . . . . . . . . . . . 26
9 . . . . . . . . Typical Specification Phrases and Inclusions . . . . . . . . . . . . . . 28
10. . . . . . . . Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
11. . . . . . . . Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4
1. EXPLANATIONS OF SYMBOLS
HAZARD AND SAFETY INSTRUCTIONS
Application range
The standard controllers of the REHAU control system for heating
must be used for process control and monitoring of surface heating
systems only.
Correct application
Trouble-free and safe operation of the REHAU control system
for heating depends on correct transport, storage, assembly,
installation and commissioning in additional to correct operation.
Electrical installation
Fuses, switches, wiring and grounds must be installed in
accordance with the local electrical installation codes.
Wiring
When installing wiring in the 230V AC low-voltage areas must be
separated to ensure segregation as defined in BS 76271 and also
to ensure protection from electric shock.
Storage and transport
The limit values listed in the data sheets are applicable for storage
and transport at all times.
Maintenance
Maintenance of the REHAU control system for heating is restricted to
regular cleaning. System components inside the switch cabinet and
living areas are best cleaned from dust and other dirt during normal
scheduled maintenance.
Installation, commissioning and maintenance of all components or the
control system must be conducted by suitably qualified competent
engineers. All electrical installations must comply to the correct edition
of BS 7671. All installation and testing must be carried out with the
power disconnected and isolated.
The control components are operated by electrical current. Improper
installation or improperly conducted repairs may cause death by electric
shock. The devices and accessories should generally not be opened.
Repairs to the device must be conducted by the manufacturer only.
Use only a dry cloth free from solvents to clean components installed
in living areas.
Never touch electrical components with wet hands or cleaning cloths!
The installers have configured the control system for the specific
building. Only the installers are permitted to modify the settings.
Incorrect configuration can result in inefficient operation of the
control system even if it operates without problems otherwise or
possibly undercooling of the floor or other areas with formation of
condensation.
Please do not modify the settings. The warranty will not apply in such
circumstances.
General information
Please take the time to read this manual carefully. Although operation
of the system is simple and self-explanatory, you can only take full
advantage of the system when you are familiar with all the important
functions of the system.
Symbols and Logos
Safety Information
Legal Information
Important Information
Information on the Web
Your Advantages
Action to be performed
è

5
èRead the safety recommendations and operation instructions
carefully and completely for your own safety and for the safety
of other people before starting assembly.
èRetain the operating instructions and keep them handy.
èIf you do not understand the safety recommendations of individual
assembly instructions, or if they are unclear, contact your respective
REHAU sales office.
Intended use
The underfloor heating systems and system components from REHAU
may only be planned, installed and operated in accordance with this
technical information. Any other use is unintended and therefore
impermissible.
èObserve all applicable national and international wiring, installation,
accident-prevention and safety regulations when installing control
systems and observe the notes in this technical information.
Areas of use not dealt with in the technical information (special
applications) require consultation with our applications department.
èPlease contact your REHAU sales office.
General precautionary measures
èObserve the generally applicable accident prevention and safety
regulations when installing REHAU control systems.
èKeep the work area clean and free of impeding objects.
èProvide sufficient lighting at the work areas.
èKeep children, house pets, and unauthorised persons away from
tools and the assembly sites. This is especially important in cases
of renovation in inhabited areas.
èUse only the intended components for the respective REHAU
system. The use of the components or tools from other companies
which are not from the respective REHAU installation system can
lead to accidents or other dangers.
Work clothing
èWear protective glasses, suitable work clothing, safety shoes,
a protective helmet and gloves.
èDo not wear loose clothing or jewellery, as they can get caught
by moving parts.
When assembling the system
èAlways read and comply with the respective operating instructions
of the REHAU controls system used.
èEnsure the floor is controlled via a separate high limit temperature
control. Details can be found in BS EN 1264. Compact mixers
supplied by REHAU can be used to confirm to this standard.
èWhen performing service and conversion work always isolate and
test to ensure circuits are fully isolated.
NOTES OF THIS TECHNICAL INFORMATION
Applicability
This technical information applies for the DIN standard and all BS,
EN and hENs standards applicable.
Navigating
A detailed table of contents with hierarchical titles and the
corresponding page numbers is found at the beginning of each
chapter.
èPlease check at regular intervals whether a more recent version
of this technical information is available for your own safety and
to ensure correct usage of our products. The date of issue of your
technical information is always printed on the bottom right on the
cover pages (e.g. 3.07 for March 2007)
- The current technical information is available from your REHAU
sales office, or downloadable at www.REHAU.co.uk
SAFETY INSTRUCTIONS
INFORMATION ON THIS DOCUMENT
2.

6
REHAU STAR CONTROLS
INSTALLATION GUIDELINES
3.
General Description
Cost effective, easy to use, stylish and reliable, it
offers the perfect solution for controlling complete
underfloor heating installations or systems
combining underfloor heating with radiators.
Although comfortable and efficient, traditionally
underfloor heating has been slow and difficult to
control and many of the solutions offered in the
market have been complex and relatively expensive.
Now, underfloor heating specialists REHAU are
set to change all that by bringing a new range of
products to the market with real ‘STAR’ quality.
Designed to operate alongside REHAU underfloor
heating pipework and manifolds and with most
types of domestic boiler systems, heat pumps and
solar heating, the STAR range includes standard,
digital and programmable room controllers and both
a wiring centre and pump/boiler module.
The range offers benefits for both the homeowner
and the installer delivering new levels of luxurious
comfort using proven, reliable technologies.
Congratulations on choosing the new range of REHAU’s STAR
Controls that brings the luxury of fingertip control of underfloor
heating systems within the reach of every homeowner.

7
3.
3.1
STAR 20
Analogue Electronic Room
Controller
Article No. 206029
Provides automatic temperature
control to improve system
efficiency and reduce running
costs. The simple dial is convenient
and easy to use.
STAR 30
Digital Room Controller
Article No. 206028
Featuring a large, easy to read
LCD display, offers simple one
touch control with integrated
night set back.
STAR 50
Programmable Room
Controller
Article No. 205576
Choose from three pre-set profiles
for separate temperature zones or
use the large text display and easy
navigation to set up your own.
Wiring Centre
Article No. 205578
Simple plug-in system which
can connect up to 6 controllers
and 24 actuator units for heating
requirements.
REHAU STAR CONTROLS
THE STAR CONTROLS RANGE
Pump Relay
Pump/Boiler logic module
Article No. 205579
Allows the pump and boiler to have a switchable function i.e.
1) Boiler fixed on time delay
2) Pump fixed run on time
STAR Centre Plus (preassembled relay and wiring centre)
Article No. 206577
Simple plug in system connecting up to 6 controllers and 24 actuators
complete with pump and boiler modules described earlier.

8
3.
3.2
REHAU STAR CONTROLS
FOR THE INSTALLER
Advanced controllers combined with a simple plug in wiring centre
and boiler/pump logic module to allow you to offer customers a
bespoke package of controls perfectly suited to the requirements of
their individual property.
The electronic Pulse Width Modulation (PWM) system used throughout
operates using a constant comparison of desired and actual
temperature. The opening period of the actuators is adjusted to avoid
over and under shoot, achieving more precise and comfortable control
of the set point desired temperature.
Night setback which can achieve energy savings of up to 30% for
homeowners is standard on all three controllers and frost protection
mode is available on the digital and programmable units.
Installation of all the units is fast and straightforward. The wiring
centre uses plug-in cable connections for up to 6 thermostats and 24
actuator units and the pump/boiler logic module is a simple efficiency
add on which enables the pump only to be switched on when hot
water is required.
Electrical installation of the controllers must be carried out in accordance
with the current wiring regulations and the connection plan. Only approved
certified professionals may carry out the installation.
To reduce call outs and to provide peace of mind for the user, a
valve protection feature automatically opens the valves once a week
to ensure that they are fully operational even when the underfloor
heating is switched on after Summer down times.
The CE approved REHAU STAR controls range has been specifically developed to work
with underfloor heating.

9
3.
3.3
This is achieved by switching off the boiler as soon
as the heating demand is satisfied so, the more
accurately this demand can be measured, then the
more efficiently the boiler will operate.
The REHAU STAR controls system uses a system
of electronic Pulse Width Modulation (PWM) to
constantly compare the desired temperature with
the actual temperature so that the boiler does not
fire unnecessarily and does not waste energy by
over or under shooting the temperature which has
been set.
Combined with a standard night set back feature
on the controllers which automatically reduces the
room temperature by 4ºC overnight, this can deliver
energy savings of up to 30%.
The REHAU STAR controls range is easy to fit
and very easy to use. Whichever stylish surface
mounted controller you choose for your home, it
can be operated either with simple dial operation or
push button controls
An integrated valve protection feature also opens
the valves once a week to ensure that there are no
problems or system failures when winter arrives.
Reliable and cost effective, the REHAU STAR
controls range is the ultimate partner for a REHAU
underfloor heating system.
Underfloor heating controls work best when they deliver luxurious
comfort levels whilst also minimising the amount of energy and fuel
used by the boiler.
REHAU STAR CONTROLS
FOR THE HOMEOWNER

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4.
4.1
REHAU STAR TECHNICAL DATA
STAR 20
Analogue
Electronic Room Temperature controller for underfloor heating which
can also be used as a standard room control systems. The controller
combines the traditional with an inbuilt specifically developed advanced
Pulse width modulated control that gives maximum control and comfort.
General
The room temperature (STAR 20) controller offers key advantages over
conventional mechanical products: This unique controller is easy to
operate using the conventional backlit adjusting dial, when illuminated
shows the room has not achieved set point.
Wiring requirements:-
Solid Wire 0.5 – 1.5mm²
Flexible Wire 1.0 – 1.5mm²
I
It is recommended that different colours are used for all electrical connections as
defined in the wiring regulations.
The illuminated dial gives the extra function of displaying when room
set point is achieved. It also offers you unique control simplicity for
heating applications of all types thanks to the high quality device
electronics.
This electronic control system ensures that the set room temperature
is maintained without fluctuation and when required a time signal
input automatically activates a reduction in temperature (night setback).
Technical Data STAR 20
Article No: 206029
Operating Voltage: 230VAC / 50Hz
Max. switching current: 10 (3) A
Hysteresis: 0.5K
Protection Rating: IP 30
Dimensions W/H/D: 85mm/85mm/45mm
Temperature range: 5°C - 30°C
Storage temperature: -20°C - 60°C

11
4.
4.2
Digital
Electronic Room Temperature controller for underfloor heating which
can also be used as a standard room control systems. The controller
combines the traditional with an inbuilt specifically developed
advanced Pulse width modulated control that gives maximum control
and comfort.
General
The new REHAU room Controller (STAR 30) is a state of the art
electronic room temperature controller which offers key advantages
over conventional mechanical products: The control device can be
easily operated by means of two buttons on the front cover.
This controller is backlit for ease of operation with a large numeric
display. It also offers you unique control simplicity for heating
applications of all types thanks to the high quality device electronics.
REHAU STAR TECHNICAL DATA
STAR 30
Wiring requirements:-
Solid Wire 0.5 – 1.5mm²
Flexible Wire 1.0 – 1.5mm²
It is recommended that different colours are used for all electrical connections as
defined in the wiring regulations.
This controller ensures that the set room temperature is maintained
without fluctuation and when required a time signal input automatically
activates a reduction in temperature (night setback).
The controller displays the current room temperature in stand
by mode, yet one touch operates the backlight facility. For extra
protection its inbuilt frost protection gives total protection for the client.
Technical Data STAR 30
Article No: 206028
Operating Voltage: 230VAC / 50Hz
Max. switching current: 10 (3) A
Hysteresis: 0.5K
Protection Rating: IP 30
Dimensions W/H/D: 85mm/85mm/45mm
Temperature range: 10°C - 35°C
Storage temperature: -20°C - 60°C

12
4.
4.3
Programmable
Electronic Room Temperature controller for underfloor heating which
can also be used as a standard room control systems. The controller
combines the traditional with an inbuilt specifically developed advanced
Pulse width modulated control that gives maximum control and
comfort with .
General
The new REHAU Programmable Room Controller (STAR 50) is a time
programmer and an electronic room temperature controller which
offers key advantages over conventional mechanical products with
its powerful time clock that offers six on/off per day seven days and
with up to six selectable profiles.
Wiring requirements:-
Solid Wire 0.5 – 1.5mm²
Flexible Wire 1.0 – 1.5mm²
It is recommended that different colours are used for all electrical connections as
defined in the wiring regulations.
REHAU STAR TECHNICAL DATA
STAR 50
This unique controller is easy to operate using the backlit display.
It also offers you unique control simplicity for heating applications
of all types thanks to the high quality device electronics.
This electronic control system ensures that the set room temperature
is maintained without fluctuation and when required a time signal
input automatically activates a reduction in temperature (night
setback) when set to switch the main wiring centre.
The powerful yet simple to use time programme has three pre
programmed profiles factory set that allows the unit to be operated
straight out of the box. All profiles can be easily adjusted to individual
temperature requirements and in addition there are two extra freely
programmable profiles and a manual mode that can be set specifically
to your needs. Large text display and self evident navigation makes
operating and setting the unit simplicity itself even with out the need
to refer to the instructions.
Technical Data STAR 50
Article No: 205576
Voltage Supply: 2 x size AA batteries (int) 230V AC / 50Hz (ext)
Max. switching current: 10 (3) A
Hysteresis: 0.5K
Protection Rating: IP 30
Dimensions H/W/D: 154mm/83mm/39mm
Temperature range: 10°C - 35°C
Storage temperature: -10°C - 60°C

13
4.
4.4
- Pump Overun
It can allow the pump to have a run on time of 3 minutes once
sensors have swiched off if required this function can be de
activated using jumpers shown.
- Pump and Boiler Delay
This can enable boiler and pump protection, for instance it delays
the turn on time for pump and boiler by three minuites after an
sensor calls for heat if required this function can be de activated
using jumpers shown
Boiler and Pump, Logic Module
This is an Intelligent electronic control interface that can switch the
pump and boiler dependant on the requirements of the main wiring
center. This unit is used to protect the boiler and pump and to reduce
cold cycling of the boiler so as to ensure there is a demand for heat
prior to switching on the boiler and pump unit.
Our experience over the years have proved that this reduce excessive
energy usage and ensures better control of the Underfloor Heating.
The pump module is optional and has the following functions:
REHAU STAR TECHNICAL DATA
STAR PUMP RELAY
Technical Data STAR Centre Pump Relay
Article No: 206577
Operating Voltage: 230V AC
Flexible cable 1.0 - 1.5 mm2
Solid Cable: 0.5 - 1.5 mm2
Ambient temperature: 0°C - 50°C
Storage temperature: -25°C to + 60°C
Protection Rating: IP 20
Current Rating: 3(2) A
Dimensions H/W/D: 85mm x 85mm x 38mm
Switch contact: Potential free
Jumper Function Default Setting
J2-Pump overrun time
ON -OFF
Jumper is ON (3
minute) position
ON - After all controller have switched
off the pump runs for an additional 3
minutes for boiler protection
OFF - Disables pump over run. When
all controller are switched off the
pump will also switch off immediately
as well
Jumper Function Default Setting
J1-Boiler and pump
protection ON -OFF
Jumper is ON (3
minute) position
ON -Enables boiler and pump protec-
tion (delays turning on pump and boiler
relays for 3 minutes when a controller
calls for heat)
OFF - Disables boiler and pump
protection (immediately turns pump
and boiler relays on when a controller
calls for heat

14
4.
4.5
REHAU STAR TECHNICAL DATA
STAR CENTRE
Wiring Centre
This is a specifically designed wiring centre interface that is used
primarily in the control of underfloor heating. Its inbuilt logic distributes
the Night set back and time signal specifically to the controller,
actuators and if installed the boiler/pump logic module. It can connect
up to six various combinations of controllers. On the output side each
zone can have a maximum of four actuators allowing in total the
facility of twenty four thermal actuators.
General
The wiring centre has an unique system of terminations and are easily
pushed into the appropriate terminals using the insertion tool supplied
with the unit.
Technical Data Wiring Centre
Article No: 205578
Operating Voltage: 230V AC
Circuit voltage: 230V AC, 5 A
Dimensions H/W/L in mm: 64 x 86.5 x 304
Safety fuse: T2A
Max. no. of controllers: up to 6
Max. no. of actuators: up to 24
Flexible cable: 1.0 - 1.5 mm2
Solid Cable: 0.5 - 1.5 mm2
Ambient temperature: 0°C to 50°C
Storage temperature: -25°C to 60°C
Relative air humidity: max 95% non condensing
Type of safety cut-out: II
Protection rating: IP20

15
Building Regulations and the Environment
REHAU have a commitment to assist building owners and occupiers
to reduce their carbon footprint. One such way of reducing the energy
used, is the effective control of heating and hot water. One way to
reduce this energy is to only burn fuel when there is a demand for
heat from the boiler, either for heating or hot water. When this demand
is satisfied, then the boiler should switch off again – it should not
be able to fire until a new demand is created by the controls. This is
called Boiler Interlock and represents the minimum standard required
under the Building Regulations for new and existing heating systems.
Valve Protection Feature
In order to ensure that the valves remain movable and functional
even after long periods out of operation - i.e. in summer, the REHAU
controller is supplied with a switchable valve exercising operation,
this ensures that the valves remain functional by operating the output
each week. This valve protection feature can be deactivated if required.
Controls are the most important points
Spending time getting the underfloor heating controls system right
for your project will pay dividends of comfort and efficiency long into
the future. Our expertise in control systems sets us apart from our
competitors.
Our controls are tried and tested by our distinguished team of experts
in controls who’s main interest is client comfort, We can provide you
with a range of underfloor heating controls, from a simple manually
mixed system to a highly sophisticated remote sensing and automated
system, accessible via BMS and the internet.
Our Control Principles
We believe that each room is unique and will therefore have its own
needs, in terms of comfort and control. As a result, it’s generally good
practice to combine individual room controls with overall system water
temperature control.
This makes sure that you achieve the comfort you require and
maximise the efficiency of the system.
Room comfort control is normally achieved using room controllers but
remember, an underfloor heating controller or room thermostat only
acts as a switch, it cannot control the heat output of the system, it can
only switch it on or off.
The heat output and therefore comfort level, of the system relates
directly to the system water temperature.
For increased efficiency, we normally operate the room controller
in conjunction with a setback control, which maintains the property
at a core temperature during off peak periods.
Night Set Back
REHAU controls offer night set back to reduce energy and this is
simply set on the STAR 50 controller selecting time of operation
and this sets all controls to a night or reduced mode of 4°C (fixed).
Electronic Pulse Width Modulating
The electronic Pulse Width Modulation (PWM) system used throughout
operates using a constant comparison of desired and actual temperature.
The opening period of the actuators is adjusted to avoid over and
under shoot, achieving more precise and comfortable control of the
set point desired temperature.
Pulse width modulation itself is a way of delivering energy through
a series of pulses rather than a contiounsly varying analogue signal.
By increasing and decreasing pulse widths, the controller regulates
the energy flow to the underfloor actuators and hence the floor.
Pulse Width Modulation (PWM)
Since the PWM control method allows the heater on when the actual
temperature is lower than the desired setting temperature, thus, PWM
control method is the best intelligent temperature control method to
control the slow responsive circuit.
5.OVERVIEW OF MAIN FEATURES
H
HHH
H
HH
L
LL
L
High
Low

16
PWM works on a setting temperature and a cycle time. The cycle time
is measured in cycles per hour (cph). PWM also uses a differential
that is centered around the desired setting temperature. The system
operates once per cycle to control the heater on and off in the
operation “triangle” (figure1).
span: rate of temp changed
t: u
p
date interval
cycle
Max.
temp
Setting
temp
Min.
temp
Span
Figure 1
In one cycle, PWM has many update intervals. Different update
intervals have different temperature. The heater on is determined by
the position of the actual temperature. If the actual temperature is
below the desired temperature in the particular update interval, the
heater is turned on (figure 2). Otherwise, if the actual temperature is
higher than the desired temperature, the heater is turned off. When
the time is changed, it will move to other update interval, the desired
temperature in new update interval is also changed. The system then
uses the new desired temperature to compare the actual temperature
to control the heater. Since different intervals have their desired
temperature, thus the operation triangle is formed.
Setting
temp.
Min.
temp.
Max.
temp
t: update interval
Heater off
Setting
temp
Heater on
t
Figure 2: Comparison in each update interval t.
The length of the heater on is determined the difference between the
desired setting temperature and the actual temperature. If the desired
setting temperature and the actual temperature is the same, the
heater is turned on for 50% of cycle time. If the actual temperature
is higher than the maximum setting temperature, the heater is turned
on for 0% of cycle time. Therefore, the length of the heater on is
determined by the change of the actual temperature.
The Δ span and span is the sensitive of the control system. If the span
is large, the heater is turned even for higher actual temperature. The
cycle time and update interval is the rate of heater on and off. If the
cycle time is long, the heater is turned on longer for in cycle time.
To Conclude
PWM is somewhat like pushing a playground-style merry-go-round.
The energy of each push is stored in the inertia of the heavy platform,
which accelerates gradually with harder, more frequent, or longer-
lasting pushes. The riders receive the kinetic energy in a very different
manner than how it’s applied.
Pulse Width Modulation
0% Duty Cycle – analogWrite (0)
25% Duty Cycle – analogWrite (64)
50% Duty Cycle – analogWrite (127)
75% Duty Cycle – analogWrite (191)
100% Duty Cycle – analogWrite (255)
5v
0v
5v
0v
5v
0v
5v
0v
5v
0v

17
6.
Design Limits
BS EN 1264-2:1997 states that floors may be raised to a maximum
of 29°C and up to 35°C in peripheral areas. For screeded floors with
maximum design surface temperature of 29°C, the floor could emit
100W/m2with an indoor temperature of 21°C.
Pipe Spacing
Based on many years of design experience, REHAU established that
pipes should generally be spaced at 200mm centres to achieve
optimum working efficiency. In areas of high heat loss, the pipe
spacing may be decreased to 150mm.
This is a guide only and REHAU would recommend a system design.
Screed Thickness
For solid floor construction, a normal floor screed can be used. No
special additives in the screed are required. Where the pipe is laid on
insulation, the minimum screed depth must be 65mm for domestic
applications and 75mm for commercial applications as specified in UK
Building Regulations. Where heavier floor loadings are required, the
construction engineer should advise on the screed thickness. Where
special screeds are specified, the manufacturer must be consulted
as to the screed thickness.
Floor Coverings
REHAU must be notified of the floor covering type before design
commences.
While floor coverings laid above the UFH system do not normally
present problems, they must be taken into consideration at the design
stage to ensure that a good design is established. After installation,
the UFH system can be “tuned” to match the variations in floor
coverings from room to room by adjusting the Lockshield valves for
the individual loops.
Timber Floor Surfaces
Careful consideration of the type of floor to be laid must be
established before the system is designed and installed. Particular
attention should be paid to moisture content of the wooden floor.
Consider if the timber floor will be floated on a screed or fixed to
battens. This will determine which type of UFH system will be used.
Not all timber floors are suitable for UFH and advice should be sought
from the flooring supplier from the trade association TRADA. Details of
the British Standard BS8201 should be observed.
Glazed Areas
In most areas of a building the heat losses are relatively similar and
unless very large areas of glass are used, the pipe centres do not
need to vary. When designing the UFH system, the warmer flow pipe
should be positioned to run immediately next to outside walls or other
potential cold spots. This ensures a slightly higher heat output in these
areas. Extensive areas of glazing in modern developments may require
special design consideration. A closer pipe spacing of 150mm may be
chosen.
In double height rooms, e.g. barn conversions or conservatories,
the pipes may be spaced at 150mm centres. During extreme winter
conditions, supplementary heating may still be required in glazed areas
such as conservatories where the heat losses are excessively high.
Positioning the Manifolds
It is important to fix the positions of the manifolds at the beginning of
the design process. The position of the manifolds should be as central
as possible in order to minimise the lengths of pipe tails and unequal
loop lengths. One manifold set typically serves a floor area up to
150–240m2.
Optimising Loop Lengths
To allow for different loop lengths, heat outputs and different floor
coverings it is necessary to balance the loops on each manifold. In
summary, the flow in short loops serving small rooms needs throttling
relative to longer loops serving larger rooms. If the loops are not
balanced, the shortest loop would “steal” all the water flow from the
longest loops, resulting in reduced heating to the largest rooms.
To help achieve flow balance in the system, loop lengths are normally
designed to be of similar length. To avoid many short loops serving
small rooms, some areas may be linked into one operating zone,
e.g. hallways, toilets and common areas. Two or more loops may be
required to serve larger areas.
GENERAL UNDERFLOOR HEATING GUIDE

18
Insulation
A layer of insulation should be laid immediately below the heating
pipes to prevent downward heat losses. For screeded floors, REHAU
normally supplies a plastic Clip Rail for fixing the pipework. Clip Rail
is laid onto the insulation to which the pipes are attached. This means
that the client can use the insulation material of his choice to lay
underneath the fixing system.
Minimum insulation thickness and type should be specified by
the architect and/or builder to comply with the current Building
Regulations.
Thermal Response Time
The better the U-value of the building and the higher the degree
of insulation, the faster the response time of the system.
In wooden suspended or floating floors, system response time is
comparable to a radiator system. However, there is no thermal lag with
these types of floor construction and good levels of insulation
are required under these systems. Where it is necessary to allow a
small gap between the insulation and the UFH system, there must be
no air movement in this air gap.
Where the UFH system is to be installed in wooden suspended ground
floors with an open void below, all air movement must be prevented
between the insulation and the UFH system to ensure maximum
efficiency from the heating system.
For systems installed in screed operating on a daily basis, the
response time is fast. This is because the temperature drop during
“off” periods of up to 8 hours is of the order of only 3°C due to the
thermal lag in the floor created by the energy stored in the screed.
By carefully setting the system time clock, comfort can be maximised
whilst minimising the system “on” time.
Sound Insulation
Depending on the type of insulation installed, the insulation will
provide a degree of sound insulation. If a specific level of sound
insulation is specified, details must be advised to the design team
before the design process begins.

19
PRINCIPLES OF CONTROLLING AN
UNDERFLOOR HEATING SYSTEM (UFH)
REHAU Underfloor Heating
REHAU Underfloor Heating is a favoured choice for industry professionals.
Practical, cost-effective and flexible, Underfloor heating is increasingly
being specified over traditional radiator systems and establishing a
reputation as the preferred modern-day heating solution.
Most common are the wet systems (using warm water), though there
are also electric (dry) systems available. Pipes are normally buried in
the screed, or run underneath the floor surface. The pipes transfer
heat from the (slightly warmer) floor into the wider room space, which
is more efficient than traditional plumber-installed radiators which
transfer heat from a relatively small and very hot surface into a much
larger and cooler space (the room).
Advantages
- Comfort – Even spread of heat provides a high level of comfort.
- Economy – reduced demand on boilers and no wasted heat at
ceiling height saves costs.
- Cost-efficiency – Reduced on-site maintenance – servicing of
boilers and pumps only.
- Flexibility – Unrestricted wall surfaces in both old and new buildings.
- Safety – No hazardous wall projections or hot surfaces.
- Control – REHAU comprehensive controls package offers a solution
for the majority of building applications.
Underfloor Heating Power Source
The heating can be powered by many types of boilers, ground source
heat pumps or even solar thermal panels, and your corgi plumber can
advise on the best boiler solution for your system. Gas, oil or solid
fuels can be used to power up the system, and the best advise is to
consult your professional plumber for the appropriate solution for your
requirements. Your plumber can further direct you to a condensing
boiler that is most suited to your system, as condensing boilers are
highly efficient and match well the requirement of the underfloor
heating system, thus operating at their most efficient point.
Underfloor Heating Considerations
Your plumber can install the REHAU Underfloor heating system
at either new property developments or as refurbishment and
redevelopment or an existing property. Your plumber will be able to
design a combined system that uses both traditional radiators and
underfloor heating. For example your corgi registered plumber can
design a system that uses underfloor heating system for the ground
floor of your home and radiators for the upper floor. Alternatively,
the plumber can advise to use wet radiators in specific rooms (e.g.
bathroom, toilet). The best advice is to use a qualified corgi plumber
that can design a heating system that is unique and bespoke to your
needs.
Further Information on Underfloor systems can be obtained from
REHAU such as:
- Explain the basic principles of warm water underfloor heating (UFH)
systems
- State the advantages of UFH systems
- Identify the design conditions and relevant standards appropriate
with UFH systems
- Carry out heat loss calculations
- Describe the floor systems and finishes associated with UHF
systems
- State the various UFH systems types of the market
- Explain the operation of UFH systems and components
Carry out UFH system design using worksheets, including working on
a project building
Zone Control
The REHAU STAR control system is a sophisticated electronic control
system that has been specifically designed to give optimum and
accurate control of FH systems. FH circuits are connected to a central
manifold. Each circuit will have a thermoelectric actuator (AC) on the
manifold operating the return valve for the circuit.
The heat output in each room is controlled by a room controller, which
continuously compares the required room temperature with the actual
room temperature. If the room temperature is too low, it will signal the
actuator (AC) to open the return valve of the circuit and allow warm
water to flow through it. (as shown in figure 3)
Zone controls give control over local/room temperature by adjusting
the amount of water circulating within individual circuits/zones.
7.

20
Adjustments are made dependent upon:
- Continuous temperature readings from each room controller
- The end user setings such as room temperature set point and
programmed night set-back periods on the timer
UFH - Manifold
AC
ACAC
HLS
IV
CP
IV
IV
ZV
UFH - Return
UFH - Flow
RT
VM
T
AC
RT
RT
RT
UFH
Control
centre
Figure 3. Individual zone controlwith FH
Constant Temperature (CT) Mixing Options
Compact Mixer Unit
- Only for domestic/light commercial applications
- For outputs up to 12kW use 1/2” valve set (not to be used to size
primary pipes)
- For outputs between 12 - 18kW use 3/4” valve set (not to be used
to size primary pipes)
- The circulating pump only circulates the warm water through the
circuits. A separate main system pump is needed to supply the
manifolds with hot water from the boiler
Working Principle
The compact mixer regulates the main system flow from the boiler
directly into the manifold. It mixes the high temperature water from
the main system flow (usually required temperature + 70°C), with
the cooler water from the FH return of the circuits to ensure the right
temperature. The thermostatic inlet valve (TIV) allows small amounts
from the main system flow to enter the return header, where it mixes
with the return water from the circuits. The circulating pump (CP)
maintains an uninterrupted flow of water from the return header up
into the flow header and back into the floor circuits as long as there is
a demand signal present from any of the room thermostats.
The temperature of this mixed flow is measured by the in-line
temperature probe, which feeds back to the thermostatic head on the
(TIV). The thermostatic head of the thermostatic inlet valve (TIV) is set
to achieve the required design flow temperature. Once the required
design flow temperature is detected by the in-line temperature probe
it closes the thermostatic inlet valve (TIV), No further main system
flow is allowed into the return header, until the measured temperature
falls below the design flow temperature. The unit also features a high
temperature limit stat (HLS) which is explained later in the section on
Temperature Safety Options.
Ω"or æ"
Ω"or æ"
Figure 4. Compact mixer unit fitted to the right side of the manifold with FH flow header on top, FH return header on bottom.