Danfoss Indoor Cable Floor Heating Systems Application guide

Indoor Cable Floor Heating Systems

Indoor Cable Floor
Heating Systems

Application manual

Intelligent solutions
with lasting effect

Visit devi.com

Index

Our quality management
system
and compliances

Along with full compliance with EU
directives and product approvals

ISO 9001 TS 16949

ISO 14001 PED

Let DEVI do the work

1. DEVI electrical heating systems 4

2. Application Briefing 5

2.1 General information 5

3. Product overview 6

3.1. Cables 6

3.2 Mats 6

3.3 Thermostats 7

4. Heating systems in floor
constructions 9

4.1. Comfort Floor Heating 9

4.2. Total (Direct) floor heating 13

4.3. Accumulating heating via
electrical floor heating system 18

5. Electrical heating system floor
constructions 21

5.1. Cable heating in thick concrete
floor construction 21

5.2. Electrical heating system in
thin floor construction 25

5.3. Heating in wooden floors 30

Appendixes 48

A.1. C-C distance and
corresponding output W/m² 48
A.2. Fitting 49
A.3. Floor sensor installation 50
A.4. General installation guide 51

DEVI - an abbreviation of Dansk El-Varme Industri – was established in
Copenhagen, Denmark, in 1942. As from January 1st 2003 DEVI has become
a part of the Danfoss Group - Denmark’s largest industrial Group. Danfoss
is one of the world’s leading companies within heating, cooling and air­conditioning. The Danfoss Group has more than 23000 employees and serves
customers in more than 100 countries.

DEVI is Europe’s leading brand of electrical cable heating systems and electric
pipe heating systems with over 70 years of experience. The production of
heating cables takes place in France and Poland while the head office is
situated in Denmark.

The value of experience

We have installed literally millions of systems across the globe, in every
conceivable setting. This experience means that we can offer you practical
advice about precisely which components you need to get the best results at
the lowest cost.

Indoor Cable Floor Heating Systems

This design guide presents DEVI’s recommendations for design and
installation of cable floor heating systems for indoor application.
It provides guidance for heating cable positioning, electrical data and system
configurations.

Following DEVI’s recommendations will ensure energy efficient, reliable and
maintenance free solution for constant wattage heating cables with 20 year
warranty.

6. Cases 52

1. DEVI electrical heating systems

This document includes all necessary
information about DEVI cable heating
systems which can be helpful in your
decision making during its design,
installation and operation. The
distinctive feature of DEVI’s profile is
production of cable heating systems.

DEVI A/S was founded in in Denmark
in 1942 and within over 75 years of its
existence it has made the way from a
private company to a large industrial
enterprise developing and providing
solutions for electrical heating
cables in more than 100 countries
around the world. DEVI takes a
leading position as a founder and
an innovator in the field of electrical
heating cable systems for indoor and
outdoor installation.
Since 2003 DEVI has being a part of
the Danfoss Group.

DEVI is the Europe’s largest supplier
of electrical floor heating. Our
business philosophy is based
on marketing electrical heating
solutions that clearly stand out as the
following:

• Increasing comfort in everyday life;

• Greater reliability;

• Better design;

• Improved operating costs.

DEVI develops, manufactures and
sells heating cable systems for the
following main applications:

• Total electrical floor heating;

• Comfort electrical floor heating;

• Ice and snow melting on ground –
roads, pavements / pedestrian
walkways, bridges etc.;

• Ice protection and snow melting
for roofs and gutters;

• Protection against freezing
and temperature maintenance
of pipelines, tanks and other
industrial applications;

• Heating of play-fields with
natural or artificial grass, soil in
greenhouses, etc.;

• Heating of agricultural premises;

• Frost protection of foundations
and floors in cold stores and ice
stadiums;
as well as many other heating
solutions.

Complete systems

DEVI is the only global company in
the industry that develops, pro­duces and markets complete systems
containing both heating cables and
thermostats in the global market.
Consequently, there is a full harmony
between the single components that
make up our heating systems, which
means high performance, optimum
reliability and usability and as a result
low energy consumption.

Integrated solutions

For almost 75 years DEVI has been
producing a wide range of proven
tested heating cable solutions –
everything from thin heating mat
systems mainly intended for renova­tion purposes, to complete heating
systems for room heating in private
dwellings as well as offices and in­dustrial buildings. DEVI also supplies
ice and snow melting solutions. Our
cables and thermostats keep traffic
areas, loading ramps and roof con­structions safe in cold areas through­out the world. We provide anti-frost
systems for pipes and roof gutters
and we heat the soil in greenhouses,
or even under football fields.

Intelligent heating systems

The main DEVI product is a complete
heating system (heating cable or
mat, thermostat and accessories).

Energy efficiency and it’s intelligent
use is built in DEVI thermostats
since the 90’s. Saving up to 30% of
electrical bill, compared with an
advanced electronic thermostat
without a timer, DEVI intelligent
thermostats are world leading
example to follow in the area of
intelligent electrical floor heating.

High quality heating elements
manufactured in EU

DEVI heating element is a screened
twin or single conductor made
with different specific outputs and
insulation options. DEVI heating
elements are produced in over thirty
different types allowing application
of the product that suits best to your
specific requirements.

Thin heating mats designed for
installation under the tiled floor are
most in demand. DEVI mats consist
of a thin cable fixed on a composite
or glass fiber self-adhesive mesh,
which makes mats easy to install and
a logical choice for thin floors. When
laying heating mats the floor level is
virtually the same since installation
can be performed with a standard
thickness of the tile glue.

System installation and calculation
of desired output shall be performed
based on specific conditions of
premises (application). To ensure
proper installation and operation of
each DEVI system it is accompanied
by multilingual detailed instructions.
In addition, most of heating cables
and mats have 20 year warranty.

DEVIreg™ Smart, the latest solution,
that is worth special attention – it
embodies the essence of DEVI
commitment to improve user
comfort, interaction with intelligent
electronic devices, Nordic design
and energy efficiency. DEVIreg™
Smart thermostat with:

• user-friendly interface via APP
and Wi-Fi control,

• touchs creen,

• intelligent timer functions with
an intuitive user-friendly interface
which is designed specifically to
meet the needs of modern users,

• extended warranty period –
5 years.

Reliable choice.

DEVI is the world leader in the
production of electrical heating
cable systems and is a part of the
Danfoss group. Presented in the
global market for almost 75 years
and available in more than 100
countries on five continents. You can
safely recommend products to your
clients as far as DEVI trademark has
occupied a leading position on the
world market and has been a trusted
partner for decades.

4 Division · Cable Floor Heating Systems · VGLUH102 · ©DEVI

2. Application Briefing

2.1 General information

Optimal comfort

All heat moves upwards! This simple
fact explains why a floor heating system
provides more comfortable heat, than
the alternative radiator system. The
radiator system provides convective
air movement up to head height and
ceiling, only to travel downwards and
return as a cold draft around ones feet.

DEVI’s floor heating system, on the
other hand, provides pleasant heat
for ones feet, body and head.

As it produces only a very gentle
upward air movement the amount
of travelling dust particles is reduced
considerably making the system a
great asset to people suffering from
allergies or asthma. It also minimizes
presence of moisture at floor level.

Minimal energy consumption

Thanks to heat distribution from the
floor and precise temperature control
system with a DEVIreg™ thermostat,
the average room temperature can
be reduced by 1-2 °C compared with
traditional radiator heating, without
influencing the thermal comfort
or even improving it. This enables
reducing energy losses, from a
dwelling, by 10-20%, which is both
economically and environmentally
beneficial.

Flexible system

DEVI’s floor heating system ensures
comfortable room temperatures, be it
at home, at the office, in a workshop,
sports hall or virtually anywhere
where comfortable heat is required.
Equally important is the fact that
DEVI’s floor heating system can be
installed in all floor types whether
they are new concrete or wooden
floors or renovated floors.

Invisible heat source

DEVI’s floor heating system is invisible.
As the system is hidden under the
floor it gives exciting new possibilities
for furnishing and interior design and
the problem of space-consuming and
unattractive radiators (or heaters) no
longer has to be considered.

Ease of Installation

DEVI electrical underfloor heating
provided as a system, be it a
heating mat, cable with installation
accessories or a thermostat with easy
setup feature, quick and effortless
installation.

High durability, no maintenance

DEVI’s floor heating system has a long
life. Practically speaking DEVI’s heating
cables and mats last as long as the
house where they are installed and no
maintenance is required!

Quick and Precise Response Time

Electrical floor heating system has
a quick response time. Along with
DEVIreg™ intelligent thermostats
it also offers precise increase and
regulation of room temperature
comparing to water based
floor heating systems. System’s
responsiveness to temperature
changes and user adjustments is
also better.

20-year DEVI Warranty™ and
Full Service warranty

20-year DEVI Warranty™ is valid
for most of DEVI heating mats and
heating cables. DEVI support Full
service warranty for cables and mats
installed indoor for floor heating –
included costs for installation and
floor materials such as damage to
bricklaying and tiles. Full Service
20-year warranty implies that
when there is a warranty case DEVI
undertakes a responsibility to
correct the defect free of charge or
offer product replacement during
the warranty period. In addition,
DEVI covers all costs associated with
the replacement of any heating
system element and floor cover
restoration costs.

5Division · Cable Floor Heating Systems · VGLUH102 · ©DEVI

3. Product overview

3.1. Cables

Electrical floor heating system
consists of two main components:

• Heating element (cable, thin
heating mat, or heating element
for laminate floors, etc.);

• Thermostat with air or/and floor
temperature sensors.

Heating cables are usually installed
in thick/concrete floor constructions.
The main feature of a thin heating
mat is its low thickness. This gives
the possibility for it to be installed
in a thin layer of tile glue avoiding
considerable increase of floor level.

internal insulation ( XLPE)

heating element (resistance thread)

DEVIflex™ heating cable construction

DEVI heating cable (e.g. DEVIflex™)
is designed for installation in thick
concrete floor constructions. Usual
thickness of top/finish floor layer is
at least 3 cm. Heating cables used in
floor constructions are serial resistive
cables, preferably twin conductor,
but also a limited range of single
conductor cable is available. Cables
are manufactured as ready-to-install
heating elements with specific length
(i.e. 7, 10, 15, up to approx. 410 m),
with a power supply cable (cold tail)
and hermitically closed connections
(muffs or end terminations).

outer PVC coating
protective screen foil (Aluminum)
protective conductor

supply cable

Output of heating cables for
installation in floor constructions is
limited to 20 W/m and DEVI cables are
available with 6, 10. 18 and 20 [W/m]
for 230 and 400 V. Most DEVI cables
are manufactured and approved in
accordance with the latest version
of IEC 60800:2009, with mechanical
strength class M2 (for rough concrete
constructions). The main type of DEVI
heating cables for installation in the
floor construction is DEVIflex™.

Internal and external design of
modern DEVIflex™ cable is shown in
the figures below.

heating cable

connecting muff

end of the heating cable

connection to power supply

DEVIflex™ 6T/10T/18T heating cable

3.2 Mats

The thin heating mat is designed
for installation in a thin tile glue
layer adhesive, self-leveling mixture
or alike. The standard minimum
thickness of the floor layer is 5-8 mm
while the thickness of DEVI mats
is 3-4,5 mm. It allows minimizing
the floor level increase. DEVI thin
heating mats consist of a thin cable
fixed on self-adhesive glass-fiber

heating cable

adhesive mesh

connection to

power supply

connecting muff

supply cable

DEVImat™ 100T/150T Heating mat

mesh usually of 50 cm width. Thin
heating cables are serial twin or
single conductor resistive cables.
Thin heating mats are manufactured
as ready-made heating sections with
a specific area (i.e. 0,5, 1, 1,5 … 12 m²)
including a power supply cable
(cold tail) and hermetically sealed
connections.

adhesive mesh

heating cable

connection to

power supply

connecting muff

supply cable

DEVIheat™ 150S Heating mat

Thin heating mats are available with
various outputs, for example: 70 W/
m², 100 W/m², 150 W/m² and 200 W/
m². DEVI thin heating mats comply
with IEC 60335-1 & IEC 60335-2-96.

The most commonly used DEVI
twin conductor heating mats for
installation in the floor construction
are DEVImat™ and DEVIcomfort™.

6 Division · Cable Floor Heating Systems · VGLUH102 · ©DEVI

Center-to-center distance between
mat’s cable lines is usually 7,5 cm. It
allows even distribution of heat on
the floor surface avoiding cold zones
between the cable lines.

The modern thin twin conductor
DEVImat™ and single conductor
DEVIheat™ are shown below.

3.3 Thermostats

DEVI heating cables and thin heating
mats mentioned above are the most
used floor heating elements. DEVI
also produces other floor heating
elements, i.e. DEVIdry™ and DEVIcell™
heat distribution panels for heating
constructions with wooden surface
(laminate, multi-layer boards,

parquet, etc.) or/and on wooden
subfloors. DEVIdry™ has 55 and 100
W/m² outputs.

For further information please refer
to the DEVI Product Catalogue.

DEVI offers specialized thermostats
for electrical floor heating systems.
All thermostats are electronic devices
allowing precise control of the
floor surface or air temperatures. In
general three types of thermostats
are available:

• for air/room temperature
control and limitation of floor
temperatures – with room sensor
and floor sensor;

• for floor temperature control –
with floor sensor only;

• for air/room temperature control –
with room sensor only.

DEVI offers thermostats that are:

• Intelligent, PWM (Pulse Width
Modulation regulated)

• Simple (hysteresis regulated).

Intelligent thermostats provide state­of-the-art wireless control system for
control of heating and electrical units
in private houses. Some thermostats
are fitted with Wi-Fi allowing remote
control of heating systems via mobile
application.

Simple thermostats are electronic
control units with or without
display allowing setting the heating
system type, adjustment of control
parameters and timer mode.

NEW!!

Adjust your
floor heating
from your
smartphone

DEVIreg™ Smart

DEVIreg™ Smart is the DEVI’s latest
solution and a further development
of, the very well known DEVIreg™
Touch with Wi-Fi control via mobile
application, unique Nordic design
and advanced user experience,
with application that enables up
to 10 different users to control
electrical heating systems from
anywhere in the world using a
smartphone or a tablet.

DEVIreg™ Smart is an intuitive
programmable intelligent timer
thermostat used for controlling
electrical floor heating elements.
The thermostat is designed for flush­mount installation into a standard
wall installation box, or on wall with
a special on-wall box. Due to the
special 2-part construction it fits a
wide range of frames and sensors.

DEVIreg™ Smart builds further on
energy saving functions introduced
earlier in DEVIreg™ Touch, like:

• fast and intuitive setup using the
built-in wizard;

• energy-saving program –
including optimum start/end
control ensuring the desired
temperature at the correct time
and thereby reducing heating
costs;

• open window function;

• very precise regulation of user set
room temperature by means of a
specially developed PWM (Pulse
Width Modulaton) regulation,
including optimal change from
comfort to economy mode.

DEVI Link
system

covers the control
of both radiator
heating and
floor heating –
individually or
combined

DEVIlink™ CC

DEVIlink™ CC (Central Controller)
is the central brain in the DEVIlink™
system which includes several
wireless DEVIlink™ devices installed
inside the building.

Several functions, i.e. room control,
intelligent timer, modes for the whole
house – “Away”, “Comfort”’, “Frost
Protection”, are integrated into the unit
to reduce energy consumption when
using electrical floor heating system.

The idea of the DEVIlink™ System is
to provide wireless connection of
your heating system and to control it
from one central point. The DEVIlink™
CC communicates wirelessly with
all other DEVIlink™ units of the
installation. A single DEVIlink™ CC
can control up to 30 rooms and
allows connection up to 50 units and
specially developed to satisfy the
needs of any family house: it can
be also used for apartments, and
multifamily buildings.

DEVIlink™ is fitted with Danfoss
Link™ App, and the latest version
provides the possibility of Wi- Fi
control by mobile application,
anywhere in the world.

7Division · Cable Floor Heating Systems · VGLUH102 · ©DEVI

DEVIreg™ Touch

DEVIreg™ 130

DEVIreg™ 330

DEVIreg™ Touch is a thermostat
fitted with a display and an intelli­gent timer. It is designed for flush­mount installation into a standard
wall installation box. It operates with
two sensors – floor wire and built-in
room sensor. It allows control setting
for one of 3 heating systems: with
wire floor temperature sensor, with
built-in room sensor or with built-in
room sensor and wire floor sensor
for limitation of floor temperature.
The touch screen menu and intuitive
user friendly interface allow easy use
and quick service. The thermostat
has four original colors – polar white,
pure white, ivory and black. It can be
installed in complex frames of differ­ent manufacturers.

DEVIreg™ Touch is fast and intuitive to
setup using the built-in wizard. It has
an energy saving program – including
optimum start/end control ensuring
the desired temperature at the correct
time and thereby reducing heating
costs.

DEVIreg™ 13x series thermostats
are designed for mounting directly
on the wall. Following models are
available:

• DEVIreg™ 130 with wire
temperature sensor;

• DEVIreg™ 132 with built-in room
sensor and wire floor sensor for
limitation of floor temperature.

DEVIreg™ 233

DEVIreg™ 233 is an electronic
thermostat designed to be flush­mounted in an installation box
from the LK FUGA series frame. The
thermostat is provided with a single
pole switch and a floor sensor (wire)
to measure and control the desired
floor temperature. Alternatively an
external room sensor can be used, for
room temperature regulation.

The thermostat has a button to adjust
the temperature setting in the range
of (0) 1 to 6.

DEVIreg™ 330 (5…45°C) – is an
electronic thermostat to be installed
in electric cabinets with DIN rail
attachment. The set includes wire
temperature sensor. To control room
temperature an external air sensor is
required.

DEVI offers over 20 different types
of thermostats. The product range
includes easy to operate (by APP)
intelligent Wi-Fi control thermostats
to specifically designed digital,
thermostats with moisture sensors
for ice and snow melting on ground
as well as ice protection for roofs and
gutters (refer to Ice & Snow melting
Application Sheet). DEVIlink™ and
DEVIreg™ Smart system is equipped
with wireless functions and Wi-Fi
control of heating systems and
indoor electrical equipment.

DEVI provides a unique solution –
that is “top quality intelligent heating
system”, giving consumers the
highest level of comfort and safety!
The intelligent component of these
systems is the DEVIreg™ electronic
thermostat which is available in
several options, i.e. for total heating
or comfort floor heating.

More information about DEVI
thermostats you can find further
in this document and in the DEVI
Product Catalogue.

DEVIreg™ 530

DEVIreg™ 53x series thermostats are
designed for flush-mount installation
into a standard wall installation box.
Three models are available:

• DEVIreg™ 530 with wire tempera­ture sensor;

• DEVIreg™ 531 with built-in room
sensor;

• DEVIreg™ 532 with built-in room
sensor and wire floor sensor for
limitation of floor temperature.

8 Division · Cable Floor Heating Systems · VGLUH102 · ©DEVI

4. Heating systems in floor constructions

Electrical floor heating systems for
indoor heating can be divided into
3 main heating categories (types):

• Comfort floor heating;

• Total or Direct heating;

• Accumulating heating.

4.1. Comfort Floor Heating

4.1.1. About the system

Comfort Floor Heating or “Warm
Floor” system provides heated floor
surface, in any rooms, and especially
used for bathrooms and kitchens.
Comfort floor heating can be used
in any room fitted with another
heating system to provide required
air temperature, for example water
based radiators on the walls. Warm
Floor/ Comfort heating installed
in such premises only maintains
constant floor temperature at all
times, regardless of the heating
season. As an additional benefit
the Comfort heating increases air
temperature in the room, and due to
large heated floor surface will allow
compensation of inadequate heating
during extremely cold winter days
or in case of lack of heat regulation
in rooms which are not fitted with
a modern thermostat controlled
room heating systems. Comfort
floor heating system is controlled
by a thermostat with a floor sensor
(usually wire sensor). The heating
element is activated by a thermostat
based on the floor temperature set
by the user.

A comfortable floor temperature
has been evaluated many times, for
example, described in standard ISO/
TS 13732-2. The maximum long term
comfort floor surface temperature
is defined at the level of 29,5 °C.
Additionally: sedentary people
needed extra 1-2 °C. For floors in
wet rooms maximum temperature
can reach 31 °C. These maximum
temperature values can be used for
calculation and selection of installed
outputs (in [W/m²]) of comfort floor
heating systems. Different types of
floor surfaces need different comfort
floor temperatures, e.g. wooden
floor surface has an optimal comfort
temperature of approximately 26
°C, carpet – approximately 24 °C.
But it is impossible to predict type

of floor surfaces during life time of
floor construction, as well as that
comfort temperature is perceived
differently by different individuals. It
is advised to use maximum comfort
floor temperature level to satisfy all
possible options, but often a floor
temperature few degrees above
the current room temperature will
already satisfy the needs of most
users. It is important that most of
wooden floor surfaces have limitation
of max. temperature at the level of
27 °C (for more details concerning
maximum allowed temperatures
of the floor surface please refer to
a manufacturer of wooden floor
materials).

EXAMPLE:

The optimal required output (in
[W/m²]) for comfort floor heating
system, can be evaluated by a simple
calculation. Assuming that the room
temperature is 20 °C (supported by
another heating system during the
heating season) and the floor surface
needs to reach up to 29 °C. The floor
temperature must be increased as
follows: 29 - 20 = 9 °С. Information
about the installed output (in [W/
m²]) needed to heat up 1 m² of
floor surface to 1 °C can be found in
physic books and standards (e.g. DS/
EN 1264. Heat exchange coefficient,
usually named alfa – α [W/(m²·K)], can
vary, however for general evaluation
α =10 W/(m²·K) can be used.

This will be described in details on
the following pages.

Consequently to heat 1 m² of floor up
to 9 °С in relation to air temperature,
approximately an installation of
9 °С · 10 W/(m²·K) = 90 W/m² is
required.

As a “rule of thumb” a safety value of
30% should also be added offering
a minimum output for electrical
heating element used in comfort
floor heating system as calulated in
the following example:
90 W/m² · 1,3 ≈ 120 W/m²

Recommendation: output for
comfort floor heating systems should
be no less than 120 W/m², unless any
special restrictions are specified.

The following power outputs for
comfort floor heating systems
are recommended based on floor
constructions, insulation levels,
surface types, room air temperature
and individual user preferences:

• Wooden floor constructions – no
more than 100 W/m²;

• Dry rooms, thermal insulated
floors – 100 W/m² or more;

• Floors without thermal insulation –
130-160 W/m²;

• Wet rooms – 150-180 W/m²;

• Low voltage, insufficient insulation,
covered balcony slabs –
160-200 W/m²;

• maximum output in floor
construction – should not exceed
200 W/m².

Find more details and restrictions for
special floor constructions such as
wood, later in this document.

9Division · Cable Floor Heating Systems · VGLUH102 · ©DEVI

Comfort floor heating systems do
not require heat loss calculation. It
is advised to install power at least
100 W/m² in all dry premises, and
at least 150 W/m² in wet premises,
however note that norms for wooden
floors specify no more than 100 W/
m², and require a thermostat with a
floor sensor to limit maximum floor
temperature. Heating system must
be controlled by thermostat and it is
worth mentioning that installation
of increased power, e.g. 150 W/m²
instead of 100 W/m² does not affect
energy consumption of the system,
but can influence user comfort
feeling.

C-C distance

Heating cables are installed inside
floor construction with some
distance between them (or so called
installation step, centre-centre
or cable-to-cable distance: C-C
distance). To achieve a warm floor
with even distribution of heat and
to provide comfortable temperature
on the floor surface, the floor surface
temperature variation should not
exceed 1,5 °С (e.g. DIN 44576).
There will always be a difference in
temperature on the floor surface, in
areas between heating cables and
directly above them. The bigger C-C
distance – thicker layer of concrete
above cable is necessary to ensure
a uniform/comfort temperature
distribution along the floor surface.
This difference is always more
pronounced during periods, when
electrical heating cables are turned
on (providing heat to the floor
heating). The instant thermostat
disconnects the heating cables,
because desired floor temperature
is reached, the temperature on the
top of the floor surface is equalized
greatly, giving an increasingly
comfortable floor surface.

A rule of thumb indicates:

• The thickness of concrete & floor
structure above the heating cables
need to be ~½ the C-C distance.

Here is the additional explanation:

For Warm Floor system installed
into a thick concrete slab the
C-C distance of 5-10 cm is
recommended. The thickness of the
concrete slab top layer is usually

not less than 3-5 cm, regardless
whether heating cables are to be
installed there or not. For thin floor
constructions, such as tile glue,
laminate etc., the C-C distance
should not exceed 10 cm and is
recommended to be even less: 7,5
cm. To install heating cables under
the tile glue the best solution is
DEVI thin heating mats with
C-C = 7,5 cm that guarantees floor
surface without cold zones.

Recommendation: it is always
advised to insulate the floor structure
below the heating cables.

More details about cable installation
step (C-C distance) and appropriate
outputs are described below in this
document.

Thermostat with floor sensor:

The thermostat uses a wire sensor to
measure the temperature inside the
floor construction. The sensor needs
to be placed directly between, and if
possible, slightly above the lines of a
heating cable or a mat. Temperature
measured by the floor sensor is
not the real surface temperature
and depends on placement of the
floor sensor. It is difficult to give
any recommendations about the
thermostat settings for a specific floor
construction.

The thermostat with a floor sensor
has a scale without degree marking.

4.1.2. System Design

Following stages will help you to find
a right solution for your comfort floor
heating system (more about DEVI
products find in the DEVI Product
Catalogue):

Choice of a heating element type
(mat or cable).

Define the thickness of floor
construction over the cable, and a
type of the installation. For example
for renovation, where small floor
structure needs to be enlarged, a
heating mat is a preferable solution
due to the element’s height.

If you plan to increase the floor
construction by less than 30 mm,
it’s preferred to use a heating mat,
suitable for floor increase of 3-5 mm.

If you plan to increase the floor
construction by more than 30 mm,
a heating cable is usually applied.
It should be noted that there are
no restrictions for use of heating
mats in concrete or thick floor
constructions. The question of
thermal insulation, installation
thickness in floor construction should
also be addressed, as it’s important to
minimize heat losses downwards.

Choice of specific output.

Specific output (p in [W/m²]), for
Comfort Floor Heating usually does
not require calculation and is selected
from recommendations for specific
floor construction and environment.
For standard floors without insulation
the output of no less than 100 W/m²
is usually chosen and for wet rooms –
no less than 150 W/m². In the lack of
reliable information about the floor
construction, flooring type, supply
voltage, etc., it is better to choose
an output as close as possible to the
maximum recommended (see page
above).

To fix heating cables DEVIfast™ fitting
bands are usually applied, it offers
a cable attachments with a step
distance (C-C) of 2,5 cm.
This leads to the situation that the
value of the specific output for a
heating cable cannot be chosen
arbitrarily, and it should be taken
into consideration that the cable can
be installed at 2,5 cm intervals only,
and respectively output will match
attachment distance.

For example if:

• cable is DEVIflex™ 18T,

• supply voltage is 230 V,

• the C-C distance of 12,5 cm
gives output of 145 W/m².
And for installation step with the
C-C of 10 cm – 180 W/m² (see the
DEVI Product Catalogue for product
selection). Thereby, for heated area
the value of the specific output - p

INST

[W/m²[, which is actually installed,
should be chosen for fixed C-C,
following the table or calculated
value.

It should be noted that in some
countries the supply voltage is lower
than 230 V that leads to decrease
of the cable specific output and
respectively, different [W/m²] with

10 Division · Cable Floor Heating Systems · VGLUH102 · ©DEVI

the same step (C-C). For example,
if the given output is 230 V the
coefficient of 0,915 should be applied
with 220 V supply.

Estimation of heated floor area.

Installation area of heating cable/mat
has to be calculated A

[m²]. To do

INST

this, from the total area of the room
(in [m²]), the area under stationary
objects (bath, toilet, shower, cabinet,
cupboards, etc.) and a strip of free
floor along walls (usually 10-15 cm
wide) is deducted, as well as special
customer’s preferences should be
taken into account.

The heating cable or mat is set
into the floor for many years, so it’s
advised to exclude from heated area
items/furniture that can be moved
over the operation life of the premises:
cupboards, cabinets, bed etc.

Along the interior walls, where
any furniture most probably will
be located up to 30-40 cm can be
allowed. For heating systems installed
in the floor construction, furniture
on legs, that provide air circulation
underneath is recommended.

Choice of a specific heating
element (length of heating cable or
area of heating mat).

Heating cable is normally chosen
based on required heating output
for room (the calculated total output

P

[W]). This output is calculated as

CALC

the chosen specific output

P

[W/m²] multiplied by the installa-

INST

tion area A
P

[W] = P

CALC

[m2]:

INST

[W/m²] · A

INST

[m²]. The

INST

heating element is selected from the
product list of factory-produced ele­ments, with specific output P

INST

[W].
Always the product nearest to, but
larger than, calculated total output

P

[W], is to be chosen. For indoor

CALC

heating DEVI recommends to use
screened twin conductor DEVIflex™ 18T,
DEVIflex™ 10T, DEVIflex™ 6T heating
cables or if nothing else is suitable, a
screened single conductor
DEVIbasic™ 20S heating cable.

The number at the end of the cable’s
name refers to: its specific output for
1 m in [W/m] at 230 V, and letter “T”
means a twin conductor cable (Twin),
letter “S” - single conductor cable
(Single).

The most frequently used cable type
is DEVIflex™ 18T – twin conductor,
18 W/m at 230 V (16,5 W/m at 220 V).
A linear output of DEVIbasic™ of
20 W/m, is not the best choice for
even temperature distribution along
the floor construction, if installed in
the same floor, compared to
DEVIflex™ 6,10 or 18 W/m.

The heating mat is selected from a
range of factory-produced elements
(covering area from 0,5 to 12 m²),
with an area covering usually the
nearest less value to available
installation space A
installation area (A

[m²]. If the

INST

[m²]) exceeds

INST

12 m², a multiplication of chosen
heating mats needs to be applied.

For example, DEVI screened heating
mats designed for floor installation
have the cable/mat thickness for:

• twin conductor of ~3,0 mm:
DEVImat™ 70T, DEVImat™ 100T,
DEVImat™ 150T, DEVImat™ 200T;

• twin conductor of ~4,0 mm:
DEVIcomfort™ 100T, DEVIcomfort™
150T;

• single conductor of ~3,0 mm:
DEVIheat™ 100S or
DEVIheat™ 150S.

The number at the end of a mat’s
name refers to its specific output for
1 m² in [W/m²] at 230 V, and letter “T”
means twin conductor mat (Twin),
letter “S” a single conductor mat
(Single). A single conductor heating
mat requires more planning before
installation, to ensure that the power
supply cord attached to both ends
of the heating mat starts and ends at
the same place.

For Comfort Floor Heating
DEVImat™ 150T and DEVIcomfort™ 150T
heating mats are used most often –
twin conductor, 150 W/m² at 230 V
(135 W/m² for 220 V ).

Calculation of the fitting band
length (DEVIfast™).

If heating cable is applied, it is
recommended to use fitting band to
fix it to the floor base. For example,
metal galvanized DEVIfast™ fitting
band. It is attached to the floor
(nailed or fixed with screws or glued)
in parallel lines, usually every 50 cm.

This equals to two (2) meters of band
for each square meter [m²] of cable
installation.

Simple calculation of the fitting band
length L

(m): cable installation

FIX

space is multiplied by two, e.g.

L

= S

FIX

· 2 (m).

INST

Thermostat selection.

Thermostat for Comfort Floor Heating
system should be fitted with a floor
temperature sensor.

Choice recommendations:

heating area is larger than 5 m² –
programmable thermostat with
timer, for example, DEVIreg™ Smart;
smaller than 5 m² – simple one
without a timer, for example,
DEVIreg™ 530 or DEVIreg™ 130, can
be chosen. Simple thermostats are
only recommended due to their
lower cost, and as there are no
restrictions for use of thermostat with
timer for small areas.

The maximum output (in Amperes),
that thermostat is able to switch on
usually varies between 3450-3600 W
(15-16 A). This needs to be taken into
consideration for larger rooms. If
more than maximum 3450-3600 W is
needed the following two solutions
are possible:

1. Heating area is divided into
independent zones with separate
cables and individual thermostats.
Each zone not exceeding the
connected output indicated
above, and with the same output
(in [W/m²]) installed;

2. Contactor (additional relay) with
increased maximum current is
used (e.g. 20 A or more), usually
mounted on a DIN rail in the
electrical switchboard.

Recommendation: it is advised to
choose thermostat load of 70-80% of
maximum installed output.

Choice of additional equipment.

Mounting box for thermostat,
conduit pipe for floor temperature
sensor, screws, nails or anchors for
attaching fitting band to the floor, etc.

It is assumed that the voltage supply
is stable and properly connected,

11Division · Cable Floor Heating Systems · VGLUH102 · ©DEVI

according to electrical laws of the
country of installation e.g. fuse and
RCD (Residual Current Device) are

of power supply cable are properly
chosen. Otherwise these elements

have to be selected too.
installed in switchboard, section and
length and cross section area

4.1.3 Design Example. Calculation and selection of equipment

Floor construction.

Follow installation instructions
provided by manufacturers of
floor elements, and local building
regulations.

Comfort floor heating for
bathroom.

Input data: bathroom, 2nd floor (over
heated room), no floor insulation,
size 3 x 4 m, total area of 12 m², with
installed 0,9 х 1,7 m bathtub, stable
power supply voltage of 230 V, floor
surface made of tiles.
Restrictions for the floor height: can
be increased maximum by 2 cm.

Heating mat or cable?

Since the floor height is an issue
the concrete thickness is less than
3 cm. Choose a mat, DEVImat™
or DEVIcomfort™ twin conductor
screened mat (find a detailed
description of products in the
DEVI Product Catalogue).

Installed output.

Wet room, stable voltage, 2-nd floor,

tiles, heated room below: an output

of 150-180 W/m² (chapter 4.1.1) is

recommended.

Calculation of heated floor space

(area of cable installation).

Out of the total space A (in [m²])

bathtub area (0,9 х 1,7 m) and strips

of floor of 10 cm along the walls are

subtracted:

A

= 12 m² – (0,9 m · 1,7 m) – ((3 m + 4 m) +

INST

+ (3 m – 0,9 m) + (4 m – 1,7 m)) · 0,1 m =
= 12 m² – 1,53 m² – 1,14 m² ≈
≈ 9,33 m².

Select the desired mat size.

Available floor area is 9,33 m².

DEVImat™ 150T covering 9 m² of

floor, and with total output of 1235 W

at 230 V, is chosen.

If the mat covering 10 m² of floor is
chosen, there will be a surplus of
0,67 m² of mat, and since it’s not
allowed to cut or shorten a heating
cables and mats, the mat covering
9 m² of floor is a preferred choice.

Fitting band.

It is not needed, since DEVImat™ has
a self-adhesive glue on the underside.
We advise to clean the floor and
remove all debris and dust.

Thermostat selection.

DEVImat™ 150T with 1235 W output,
less than 3450- 3680 W maximum

allowed, can be connected to a
DEVI thermostat. For the heating
area exceeding 5 m² – thermostat
with a timer is recommended. For
example, choose the most modern
programmable WiFi thermostat with
intelligent timer – DEVIreg™ Smart.

Type System Temperature sensor Range IP class Load, max.

DEVIreg™

Programmable:

Air: embedded,

Floor 5…45 °С.

IP21 3680 W

Smart

Comfort Floor Heating or Heating
with floor temperature limiting

As an option, simple thermostat
with floor sensor can be chosen:
e.g. DEVIreg™ 530. When thermostat
is installed in a wet room, the
requirements of electrical safety
norms and corresponding IP
class should be strictly followed!
It is recommended to install the
thermostat outside the bathroom.

Additional equipment.

Electrical materials necessary for
installation will typically include
the following: wall mounting box
for thermostat, 4-5 m conduit pipe
for a floor temperature sensor and
additional power supply if necessary.
It is assumed that there is a proper
power supply, according to the rules

Floor: included wire
sensor

Air 5…35 °С

and regulations for safety elements
of electrical installation, e.g. fuse and
RCD are installed.

Summary:

For comfortably warm floor in 12
m² bathroom (with free area of 9,33
m²), the following DEVI floor system
elements are recommended:

Equipment Characteristics Quantity

Twin conductor screened DEVImat™ 150T

9 m² 1235 W (at 230 V), (150 W/m²) 1 pcs.

heating mat
DEVIreg™ Smart thermostat Programmable, WiFi, APP enabled, intelligent timer,

1 pcs.

air and floor sensors, IP21
Conduit pipe Ø 16 4 m
Mounting box 1 pcs.

12 Division · Cable Floor Heating Systems · VGLUH102 · ©DEVI

4

2,3 1,7

0,1

0,9

3

Temperature sensor in corrugated pipe

0,5

0,075

C-C distanceConnection muff

Thermostat

Figure 1 – Example of heating mat installation in bathroom. All distances are in [m].

4.2. Total (Direct) floor heating

4.2.1. About the system

Total or Direct electrical floor heating
is the only heating system installed
in a room (or area) for maintaining a
user specified room temperature. It
is ensured by adjusting floor surface
temperature, due to the changeable
heat transfer from the surface of
the floor. Such a system is regulated
by a thermostat with air & floor or
only room temperature sensor. Air
room sensor is an integrated part
of DEVIreg™ room thermostats. A
floor heating system has a large
heated surface of the floor, and it is
a convection and radiation heating
system. Advantage of a floor heating
system is to provide heat in the
lower part of a room near legs and
relatively less heat around room
ceiling, where it’s not so highly
needed. It is proven by many studies,

that such temperature division is the
most comfortable for any person,
independent of gender, age and
activity level. Floor heating system
provides a feeling of the same or
improved thermal comfort at lower
overall room temperature setting.

As a result, it can be lowered by app.

1...2 °C, compared with an earlier
used radiator heating system, with
heating element installed visibly
under the window. This provides a
user with improved thermal comfort
and energy savings of approximately
10-20%.

Output of a heating system is chosen
based on the level of calculated
heat loss (in Watts). Energy, which is
provided via a floor heating system,
must cover heat loss and support
a specified air (room) temperature.

End muff

Usually a safety factor of 20-30% is
added to the heat loss calculated
output value, depending on room’s
specific thermal condition. As the
heating system is controlled by a
thermostat, installing larger power
output does not affect the overall
consumption of electrical energy for
heating.

Total electrical floor heating, “Heating
via floor” should not be confused
with “Comfort Floor Heating/Warm
Floor”. The need for warmth is
variable, because of the changing
outside temperatures during the
heating period, and accordingly
floor temperatures varies too. As
an example, in October, when the
outside temperature is +5 °C, it
would be enough to heat the floor
up to 21...22 °C to maintain indoor
temperature of 20 °C. But in February,

13Division · Cable Floor Heating Systems · VGLUH102 · ©DEVI

when the outside temperature is
lower e.g. -15 °C, floor will be heated
more e.g. 25...26 °C, to maintain the
same room temperature.

When utilizing floor heating system
for total heating you should always
choose as technically correct
solution, but observe the limitation
of the maximum floor temperature.
For regulation of a total heating
system a thermostat measuring
air (room) temperature and fitted
with floor temperature sensor is the
preferred choice. Allowing setting
maximum floor temperature level
and constantly monitoring prevents
overheating of floor. Such limitations
are strictly necessary for floors with
wooden surface.

Special DEVI thermostats are used
where setting of the maximum
floor temperature is necessary or
advisable:

• in programmable models: by

setting of special option.

• in simple models: by manual
potentiometer under the
thermostats cover.

Factory default setting for maximum
floor temperature limit is 35 °C.

Even if a specific floor installation
doesn’t particularly require a floor
sensor to be installed, it’s strongly
advised to do so. Install a plastic pipe
conduit where, at later date, floor
sensor could be fitted. The heating
element (cable or mat), is installed in
the floor construction where it forms
parallel lines. When using a heating
cable: output density of heating
system (in [W/m²]) is determined
by C-C distance (cable-to-cable or
center-to-center distance) of heating
cable. Increasing the distance
between cables leads to decreasing
of output and vice versa. When a

desired output density is calculated
and chosen, than C-C distance,
that will determine the number of
cable lines per 1 m² of floor or the
cable length per 1 m² is calculated.
Multiplying the chosen cable length
on a total area of heating cable
installation will give the calculated
length of heating cable.

C-C distance (cm) =

Available floor area (m²) · 100 (cm/m)

=
Length of chosen cable (m)

Detailed information about cable
installation procedure is found later
in this document.

For modern houses or dwellings
calculated heat loss is small and,
consequently, the output of floor
heating system is also limited. As a
result, to prevent a heating cable
from being installed with a large C-C
distance, it’s advisable to use one
with less linear output. For example,
for calculated heat loss of 50 W/m²,
when using the most common
DEVI cable: DEVIflex™ 18T, the C-C
distance will be as big as 36 cm. That
will inevitably lead to a floor surface
pitted with cold zones situated
between lines of the installed heating
cable. As aim for a floor heating
system is to achieve and maintain
a constant and comfortable floor
temperature, for heating systems
with required low specific output,
we recommend heating cables with
lower linear output (in [W/m²]): for
example DEVIflex™ 10T or DEVIflex™ 6T.
This allows reduction of C-C
distance and leads to a more even
temperature division on the floor.

Safety coefficient.

For heating systems installed in
floor structure, it’s necessary to add
a safety coefficient of 1,2-1,3, when
designing a power output that needs
to be installed in the floor. This factor
is an experience value used by the
industry, and is based on following
facts:

• heating cables length, resistance
and wattage tolerance,

• power supply voltage has some
accuracy,

• heat loss downwards, floor
buildup, and surface material type.

Floor surface temperature.

It should be taken into account that

the big heat loss leads to necessity
of big output from a heating
system and, accordingly, to high
and perhaps not a comfortable
temperature on the surface of the
floor. The maximum temperatures
of the floor surface for different
types of applications are specified in
the relevant standards. For a rough
estimation of the possible floor
temperature for a given output the
value of heat exchange coefficient of
α =10 W/(m²·K) (more description is
found in paragraph about Comfort
floor heating) should be used. For
example, if the output of the heating
system is 150 W/m² and heat loss
down is ~ 20%, than the heat flow up
is 150 – (150 · 20%) = 120 W/m².
If actual heat loss is close to that
value, it will imply a requirement
of an increase of a floor surface
temperature with as much as 12 °C
(120 W/m² /10 W/(m²·K) in relation
to air temperature. E.g. if the air/
room temperature is 18 °C, the floor
temperature can reach 18 + 12 = 30 °C
in the coldest time of the year to
satisfy the rooms actual heat loss.

4.2.2. Calculation and selection of
elements/products

For more detailed information refer
to the DEVI Product Catalogue and
previous chapters of this document.

Estimation of a heating system’s
calculated output.

Define heat loss of the premises
Q [W]: from documentation or by
calculation (e.g. EN 12831).

Floor heating system calculated
output is determined with taking into
account a safety factor of 1,3:
P = Q · 1,3 [W].

Choice of a specific heating
element (mat or cable).

Define the thickness of floor
construction over the cable. If
planned concrete height is 3 cm
or more, heating cable is usually
installed, if floor construction is thin
(tile adhesive, etc.), heating mat
(with thickness of ~ 3-4,5 mm) is a
preferred choice. It should be noted
that there are no restrictions for use
of heating mat in concrete or thick
floor construction.

14 Division · Cable Floor Heating Systems · VGLUH102 · ©DEVI

It’s strongly advised to install
insulation in the floor construction
if possible. Its thickness should be
selected according to local norms.
When heating system works for a
fairly long period during the year
(e.g. in the Nordic countries for
6-8 months per year), thickness of
thermal insulation in the floor has a
direct influence on level of heat loss
and therefore additional electricity
costs. For the durability of the floor
construction concrete installed
over/onto insulation, has to have
a thickness of at least 3 cm and be
in accordance with local building
norms.

Estimation of heated floor area.

To estimate installation area of
heating cable or mat A

(in [m²]):

INST

deduct the area, where cable is not
installed, from the total area of the
installation (room). It’s recommended
that strip along the walls without
cable/mat has width of ~ 10-15 cm
and along the interior walls, where
furniture will be most probably
installed, is within 30-40 cm.
For heating systems in the floor
construction, furniture on legs
(min. 5 cm of air gap to the floor) is
advised, allowing airflow underneath,
so the cable/mat under the furniture
will not overheat.

Estimation of the calculated output
per [m²].

Specific calculated area output, p

CALC

[W/m²] is calculated by dividing the
calculated heat loss Q [W] by the
installation area A

p

= Q / A

CALC

INST

[m²]:

INST

[W/m²].

It should be noted that the calculated
output is typically slightly less than
real chosen output of heating cable,
which is installed in the floor. This
is due to the fact that cable can be
attached on DEVIfast™ fitting band
with a fixed distance of 2,5 cm (or
multiplication thereof) only.

Choice of length of heating cable
or area of heating mat.

Total cable/mat output should not
be less than the calculated heat loss,
including the safety factor of 1,3.

Heating cable.

Cable is usually fixed with help of
DEVIfast™ metal fitting band, with
cable attachment points every 2,5 cm
and allows to implement different
fixed output on 1 [m²]. This fact
should be taken into consideration
during calculation of a specific
solution. For example, if the cable is
DEVIflex™ 18T and supply voltage
is 230 V for C-C distance of 12,5 cm,
output is 145 [W/m²], and for
C-C = 10 cm – 180 [W/m²]
(See also Appendix A.1).

It should be noted that in some
countries supply voltage is lower
than 230 V, which leads to a decrease
in cable output and, respectively,
different [W/m²] with the same
installation distance. For example

at 220 V electrical supply, the output
form a heating element, rated at
230 V is only 91,5% (coefficient
0,915 should be applied to heating
element output from DEVI Product
Catalogue).

For heating cable with defined
installation C-C distance, a specific
output p

[W/m²] is selected,

INST

with help of a product table or
calculated using the formula. Usually
a product with nearest larger value
to calculated output p

is chosen.

CALC

This chosen/calculated output will
be the actual output for 1 m² of the
heating system. In other words, it is
area specific output p

[W/m²] of

INST

selected heating cable installation
C-C distance.

Heating cable total output p
calculated as the specific output p

CALC

[W] is

INST

[W/m²] multiplied by the installation
area A

p

CALC

[m²]:

INST

[W] = p

[W/m²] · A

INST

INST

[m²]

Cable is selected from a list of factory
produced products, with output

p

[W], usually the nearest larger

INST

to calculated output p

[W]. The

CALC

nearest lower output can only be
recommended, if it differs from the
estimated no more than ~5%.

Output of the selected cable is
the actual output of the heating
system.

For total room heating DEVI
recommends to choose screened
twin conductor DEVIflex™ 18T,
DEVIflex™ 10T, DEVIflex™ 6T heating
cables or, only if necessary, a single
conductor DEVIbasic™ 20S heating
cable.

The number at the end of the
cable’s name refers to its specific
output for 1 m – W/m at 230 V,
letter T – twin conductor cable
(Twin), letter S – single conductor
cable (Single).

In floor construction the most
frequently used cable is
DEVIflex™ 18T – twin conductor,
18 W/m at 230 V.

Heating mat.

When installing thin heating mat, it
is chosen with a specific output

p

[W/m²] the nearest larger to

INST

calculated output p

. However

CALC

installation also needs to look at
the available floor area A
and choose a mat, that covers an
area close to available. Otherwise
installation will leave unheated
and cold floor areas, resulting in
users dissatisfaction with the total
heating system.

For example, DEVI screened heating
mats designed for installation in
floor construction:

• twin conductor of ~3,0 mm:
DEVImat™ 70T, DEVImat™ 100T,
DEVImat™ 150T, DEVImat™ 200T;

• twin conductor of ~4,0 mm:
DEVIcomfort™ 100T,
DEVIcomfort™ 150T;

• single conductor of ~3,0 mm:
DEVIheat™ 150S.

The number at the end of the mat’s
name refers to its specific output for
1 m2 in [W/m²] at 230 V, letter T –
twin conductor mat (Twin), letter S –
single conductor mat (Single).

INST

[m²],

15Division · Cable Floor Heating Systems · VGLUH102 · ©DEVI

For example, DEVIcomfort™ 100T
heating mat is a twin conductor,
100 W/m² at 230 V (91 W/m² at 220 V).

Output of the selected heating mat
will be the actual output of the
heating system.

Calculation of the length of the
fitting band.

If heating cable is chosen, it is
recommended to use fitting band
to fasten it to the floor base, for
example, galvanized DEVIfast™
fitting band. DEVIfast™ is usually
attached to the floor (screwed,
nailed or glued) in parallel lines
spaced every 50 cm, but not more
than 1 m. As a result, approximately
two meters of band for each square
meter of installation area are used.

Calculation of fitting band length

L

(m) - cable installation area is

FIX

multiplied by two:

L

= AS

FIX

· 2 [m].

INST

Alternatively, if installation allows,
heating cable can be fixed to metal
reinforcement mesh placed in the
floor construction with help of
DEVIclip™ twist.

Choose a thermostat.

Thermostat designed for electrical
floor heating system for total
heating is fitted with an internal
air temperature sensor and
usually with an additional floor

temperature sensor (included
with thermostat). The floor sensor
allows controlling and limiting the
maximum temperature of the floor
surface. This restriction is often
mandatory and standardized for
some producers of floor coverings,
e.g. for laminate or parquet boards.

Following is recommended, if:

• heating area is larger than 5 m²:
programmable thermostat with
timer, for example, DEVIreg™
Smart or DEVIreg™ Touch

• heating areas is smaller than 5 m²:
simple thermostat without timer,
for example, DEVIreg™ 532 or
DEVIreg™ 132, can be chosen.

Simpler thermostats are only
recommended in terms of their
lower cost. But for heating system
thermostats with timer are the
most energy-efficient choice, since
there is a possibility to save energy
during the absence of people in the
room, e.g. reduce temperature in
the room at night.

Thermostats have an internal
relay that has a limitation of the
maximum output (Amperes), that
thermostat can switch on: typically
3450-3680 W (15-16 A).

In case of need to install more than
maximum 3450-3600 W, following
two solutions are possible:

1. Heating area is divided into

independent zones with separate
cables and individual thermostats,
each zone not exceeding the
connected output indicated
above, and with the same output
(in [W/m²]) installed;

2. Contactor for proper current
isused (additional larger relay),
usually mounted on a DIN rail in
the switch panel.

Recommendation: it is better to
choose thermostat load at 70-80%
of maximum.

Choice of additional equipment.

Mounting box for thermostat,
conduit pipe for floor temperature
sensor, nails or anchors for
attaching fitting band to the floor,
etc.

It is assumed that the voltage
properly supplies the place of
the thermostat installation, e.g.
fuse and RCD are installed in
switchboard, section and length of
power cable are properly chosen,
etc. Otherwise these elements have
to be selected too.

Floor construction.

In multi-layer floor construction,
consisting of many elements, a wide
range of considerations need to be
made. Always follow the national
rules for construction and in case of
uncertainty get in contact with your
local DEVI product supplier.

Example. Direct Floor Heating – calculation and selection of equipment

Total heating system for new build
living room.

Total heating via electrical floor, using
the heating cable including limiting
of maximum floor temperature.

Data:
Room size 3 x 5 m, total area of 15 m²,
concrete floor, stable supply voltage
230 V, ground floor, concrete is
assumed more than 3 cm thick,
calculated heat loss is 1100 W.

Definition of cable system’s
calculated output.

The calculated heat loss Q is 1100 W
or per [m²]: 73,3 W/m². To select cable
heating systems take into account
the safety factor of 1,3, the calculated
output is: P = 1100 · 1,3 = 1430 [W].

16 Division · Cable Floor Heating Systems · VGLUH102 · ©DEVI

Choice: heating mat or cable.

Concrete is assumed not less than
3 cm thick, floor construction is
“thick”. Twin conductor screened
DEVIflex™ 18T heating cable is
chosen for installation.

It is assumed that insulation of
necessary thickness will be laid under
the cable, so downward heat loss is
minimal and does not require taking
into account.

Estimation of heating cable or mat
installation area.

It is proposed that the cable is placed
at a distance of 10 cm (0,1 m) from
the 3 m length outer wall and the
same from opposite wall with the
door. There are no other permanent

(fixed) installations in the room,
limiting the availability of the floor
area. Under these assumptions for
3 x 5 m room the area for cable
installation is:

A

= 15 m² – (3 + 5 m) · 0,1 m –

INST

– (5 + 3 m) · 0,8 m =
= 15 m² – 0,6 m² – 3,2 m² =
= 11 m²

4. Estimation of the calculated

output per 1 m².

The calculated heat loss Q [W] should
be divided into cable installation area

A

[m²]:

INST

p

CALC

= Q / A

= 1430 W/11 m² =

INST

= 130,3 ≈ 131 W/m².