Frequently Asked Floor Heating Questions


How to fit new DEVI electrical heating mat?
Fitting a DEVI heating mat is simple to do by yourself, should you choose to install it. However, please note that all electrical connections must always be carried out by a qualified electrician. Step 1 Start by measuring the area where you want your floor heating. This way you can determine the size of DEVI heating mat you need. Always select a heating mat package that is slightly smaller than the floor area. Step 2 Mark the positioning of the toilet before you remove it. This helps you avoid placing the toilet on top of the mat, and prevents you from piercing it with screws. Step 3 Cut a 10 mm-wide groove into the floor and wall from the thermostat and about 1 mm out into the floor, for the floor sensor and tube. Glue the tube that houses the floor sensor into the channel and seal the end of the pipe with duct tape. Step 4 Before laying the self-adhesive mat, your existing floor should be clean, dry, and primed, if necessary. Once the mat has been tested, it can be rolled out and laid on the floor. Step 5 Roll out the mat. When reaching the end, simply cut the mesh, turn the mat and lay the next strip close to the first one. The red heating cable must NOT be cut. The mat can withstand 3-5 adjustments as long as you do not press the mat to the floor. Step 6 When you are satisfied with the result, press the mat to the floor. DEVImat™ will now adhere firmly to the surface Step 7 Cover with one layer of flexible tile adhesive/self-levelling compound, and allow it to dry before tiling or lay the adhesive and tiles in one operation. A flexible adhesive and grout should always be used. Step 8 Mount the new tiles on the adhesive. Joint the tiles and let the floor dry for two weeks before turning on the heat.
What is the width of the mat?
The actual width of the mat is 480 mm, but it is recommended that it be laid at 500 mm intervals to ensure the correct gap between runs is achieved.
What is the difference between twin & single conductor mats?
The difference between the two is the ‘cold tail’. With the twin conductor, there is no second connection tail to return to the thermostat. With the single conductor there is a cold tail at each end of the cable or mat and they have to be brought back together at the connection point. The twin conductors have a very low Electromagnetic radiation (EMF). Both the single conductors and twin conductor cable and mats are well within recommended EMF standards.
What is the black thing at the far end of the twin conductor mat?
This is the connection at the end of the twin conductor mat where the heating element is connected to the neutral return. This is manufactured within the cable.
The DEVImatTM is too big for the room. Can I cut it?
No, the electrical heating mat cannot be shortened as this will alter the resistance of the element, which may lead to overheating. It is therefore important that the area to be heated is measured accurately (free floor area only) and that you select the closest smaller area element. Please ask your DEVI Supplier for help. Mesh can be cut, but take care to not cut or damage a cable.
I have a large area that requires two mats. How do I connect them together?
The cold tails/leads have to be brought out of the floor and have to be connected in parallel, e.g., core colors connected together, brown with brown, blue with blue, etc. into a thermostat.
The fuse keeps blowing when I use the mat. What should I do?
CONTACT YOUR ELECTRICIAN. Fuses can blow or circuit breakers can trip on either short circuit or overload, short circuit being the most common cause.
What floor finish is suitable for use with the DEVImatTM system?
Most floor finishes are suitable for use with underfloor heating, provided the floor has been prepared correctly and any manufacturer’s temperature guidelines have been followed. With finishes, such as wood laminates and carpets, it is essential that the heating mat is completely covered with a suitable floor leveling compound before the specified finish is applied. Moreover, for flooring, such as laminate, wooden parquet or carpet, we recommend DEVIdry™ solutions as well as the use of a thermostat/regulator with a floor sensor.
Do we need insulation with DEVImat products?
The DEVImat is designed to be laid directly onto an existing floor surface, so it does not require insulation. However, if there is room within the floor to add insulation or a tile-backer board, we strongly recommend this as it will enhance performance and reduce operating costs. Please contact DEVI for information.
Does the floor need to be primed before laying the DEVImat?
The mat has an adhesive backing; if the floor is dusty or greasy, it will not stick particularly well. Priming the floor will significantly help the mat to fully adhere to the floor surface.
I want to use DEVImat underneath a laminate flooring, what type of underlay do you recommend?
The underlay that is usually supplied with wood laminate is an acoustic about 2-3mm thick; this is acceptable. If you are installing anything else, please call our technical team at DEVI for advice. For laminate, we recommend DEVIdry solution.
Can I put the DEVImat underneath a bath or shower tray or kitchen units?
DEVI does not recommend any heating to be installed under such fixtures for a number of reasons. 1. It can inhibit the flow of heat being produced from the system 2. If ever a fault was to occur, it can be very difficult to carry out a repair.
I have a floor which is made up of both timber and concrete. Can I use a single heating mat for the floor?
DEVI strongly recommends that each section of floor with a different covering has its own ‘mat’ as well as thermostat since each floor surface has a different maximum temperature limit. We advise to use a thermostat with a floor heating sensor. Contact DEVI to discuss the best options for this floor.
I have a tiled floor over both a timber and a concrete floor structure. Which mat should I use?
DEVI would recommend that each section of floor has its own ‘mat’ and thermostat. In this case, each mat would have its own floor sensor preventing an uneven temperature between the two floor areas. DSVF-150 would be recommended for the concrete floor and DTIF-100 would be recommended for the timber floor.
Can floor heating be installed into a thin adhesive bed?
Yes, it is possible to install a DevimatT on top of most existing floor surfaces, including concrete, timber, fibre cement sheet and existing tiles using a thin adhesive bed or levelling compound.

Cables and Mats

My electrical heating mat or cable has been damaged/broken. Can I fix it?
Yes, all mats and cables can be repaired. DEVI offers a comprehensive and accurate fault (location) finding service. Contact us more details.
Can I extend the cold tails/sensor cable?
Cold tails can be extended based on wire length, specific output, cross sections, but it needs a separate calculation. Please contact your local technical support. In the case of a broken cold lead a equal length of the same cross section and type cold lead can be used as a replacement when mounted by authorized personnel. Sensor cable can be extended up to 100 m without contacting local support, using the same cross sections of wires (e.g. 0,75 mm2). For longer lengths please contact local technical support.
What is the maximum floor finish thickness I can have with DEVImat/DEVIlex heating cables?
This will depend upon the finish specified. For timber surfaces: 20mm for soft wood; 30mm for hard wood; most wood laminates are OK, but may need to be treated on merit. Talk to your floor covering supplier. Most vinyl floor coverings are suitable as long as you adhere to the manufacturer’s temperature limits and the elements are encased within the floor or a surface screed/FLC. Most carpets and underlays are suitable.
What type of power supply do I need?
This will depend upon the area being heated and the density of electrical heating cable/mat installed. Typically, we install at approx. 140 to 150 W/m² of heated floor area. Contact an installer recommended by DEVI for advice.
Is underfloor heating suitable for use underneath carpets?
Yes, provided the mat/cables are first covered with latex floor leveling compound, and the carpet used with a floor heating system is certified, approved, and confirmed by its manufacturer.
If the heating cable is damaged can it be repaired?
Should a cable be damaged either during or after construction, the location can be detected using special testing equipment. Repairing a cable is normally straight forward and can usually be confined to a small area.


What is a ‘floor sensor’?
A floor sensor is a device that is connected to the thermostat, and allows the floor temperature to be fully controlled.
Where is the floor sensor wired?
The floor sensor is wired back to the thermostat, and connected to the “NTC” terminal. There is no polarity on the cables.
Is the floor sensor necessary? I haven’t installed one.
DEVI always recommends to install a floor sensor. The DEVIreg Touch / 550 / 535 / 540 thermostats can be programmed to operate as any 1 of these 3 options: Air sensing. Floor sensing only. Air & floor sensing. A Floor sensor must be installed when floor or floor/air sensing is chosen. Without a floor sensor, the maximum floor temperature cannot be controlled. A floor sensor is essential with wood, vinyl or carpet floor coverings.
Away mode of DEVIreg Touch – what is the timing?
The heating will start and end the away mode at the beginning (00:00) of the day. If the start day is today, then away mode starts immediately.
Can the backlight in stand-by mode be turned off on the DEVIreg Touch thermostat?
Yes it can. From the main menu, go to Settings > Options > Dim level, and select OFF. With the same navigation, the safety lock, forecast (adaptive function, both start and end), window open and min. floor temperature can also be turned off.
What are the PWM cycle times on DEVIreg Touch?
Twenty minutes in room regulation mode and 20/40/60 minutes in floor regulation mode or room/floor regulation mode. The time depends on the response time of the floor (light/heavy floor).
DEVIreg Touch - How can you unlock the safety lock again?
Temporary unlock by pushing the quick button on the side. To unlock permanently from the main menu, go to Settings > Options > Safety lock, and select OFF.
DEVIreg Touch - Can a front part be used with any back part?
Yes it can. The back part only contains a relay, power supply, and terminals.
What do I do if ‘Unrecoverable Error’ appears on the DEVIreg Touch?
1. Turn the thermostat off at the mains, and turn it back on again. 2. If this doesn’t resolve the issue, the back section and the front section are not connected properly. The user should remove the front section and the back section, move it forward then try putting the front section back on again. This should resolve the issue.
What do I do if ‘Floor Sensor Short Circuited’ appears on the DEVIreg Touch?
This indicates the 2 cores are touching on the floors sensor, which happens if the sensor has been damaged. If this is the case, you can start by checking the wiring on the back of the thermostat to make sure there are no loose connections. If the connections are okay, then you will need to test the resistance of the floor sensor using a multimeter; it should get a reading of between 10-20 kohms. If the reading is significantly lower or higher than this, the floor sensor is damaged and will require replacement.
Can I use DEVIreg touch with other manufacturers floor sensors?
Yes you can. The DEVIreg Touch works with floors sensors from DEVI, Warmup, Aube, OJ, Eberle, Ensto, Fenix, Raychem, Teplolux and many others.
What does the target symbol mean in the bottom corner of my DEVIreg Touch?
The target (3 circles) symbol on the bottom right of your screen indicates a point to press the screen if you wish to wake it up.
What does the hand symbol mean on my DEVIreg Touch?
The hand symbol in the top left corner indicates the timer function is off, and the thermostat is operating in manual mode.
What do the arrows going up mean on the left of the temperature screen of DEVIreg Touch?
These arrows indicate the thermostat is providing power to the underfloor heating system, and it is currently warming up.

Troubleshooting & Support

The system is not heating up. What should I do?
There are a number of reasons why this could happen: * Check that you have a supply (voltage) to the thermostat. * Check to make sure the thermostat is operating. * Check the settings on the thermostat. * Check the continuity and resistance of the mat. These checks should be carried out by a qualified electrician.
Can we get a DEVI technician to come out and look at the system?
Yes, contact us to discuss your issues and schedule a site visit if needed. Most issues can be resolved over the phone.


What type of tile adhesive/leveling compound/tiling grout do you recommend?
The covering has to be flexible or have a flexible additive. Talk to your tiler for advice.
How thick does the layer of tile adhesive/leveling compound need to be?
The adhesive bed has to be thick enough to cover the cables; generally 4-5mm is sufficient.
How long do I have to leave the heating system, after tiling, before I can switch on?
DEVI would recommend that the adhesive used is allowed to dry/cure naturally and to follow manufacturer’s recommendations. Turning the floor system on too early can result in damage to the floor (to quick drying out).
How long do I have to leave the heating system, after screeding, before I can switch on?
It is recommended that any screed be allowed to cure naturally, and this would also depend upon its thickness. Generally, the length of time from the screed being laid and the system being ready to switch on is sufficient for it to dry out.
Installation - Required output
The required output heat can be anything from 40-150 W/m². It must be based on a detailed calculation of the room heat loss in W/m² from an architect, consulting engineer or your local DEVI Office. The next step is to determine the heatable floor area heat. This means that the area covered by cupboards, bathtubs, lavatories, etc. has to be deducted from the total room area of a room. In order to ensure a quickly responding heating system, the total calculated output has to be increased by approx. 30%. The required output can now be found heat [W/m²] = 1.3 x room x room/heat.
Installation - Rim zones
Locally, the output may be up to 2 times higher, e.g., in front of larger window areas. These rim zones are achieved by reducing the distance between the cables.


What is total heating?
Total heating, also called primary heating, means that electrical floor heating is used as the only source of heat in a house. DEVI floor heating is an effective heating system that can easily heat up your house as the only heating source. The DEVI total heating system is designed to cover total heat loss and provide full heating. Normally, DEVIflex™ heating cables are placed in the lower part of a reinforced concrete layer with a maximum thickness of 5 cm.
Are there restrictions on what furniture I can have on top of my underfloor heating system?
Underfloor heating relies on the heat produced being unrestricted. If it is restricted, it may cause “hot spots” and, at worst, discolor the floor. Things such as beanbags, mattresses laid directly on the floor may cause problems. Any object that allows air movement underneath it is OK.
How long does the heating system take to warm up?
This depends on various factors, such as: * What system has been installed and where (under tile or in slab)? * Type of screed that has been laid? * Depth of the floor screed? Warm-up time could be anything from 30 minutes for a DEVImat placed under tiles through to 5 – 7 (or more) hours for an in-slab storage system.
Can suspended slabs be heated?
Yes they can. However, the exposed underside of the slab must be insulated to minimise downward heat losses. Styrofoam and/or polystyrene insulation boards are often used.
Is supplementary heating required?
If steady 24 hour a day warmth is required, the building is well insulated and the correct electricity tariff is used, then generally no supplementary heating is required. However, timber floors may require supplementary heating because the amount of heat permitted under a timber floor is limited.
Do the systems require any maintenance?
No. They are virtually ‘maintenance free’ because there are no moving parts to break down, with no grills or ducting to clean and maintain. Compared to alternative central heating systems such as ducted gas or Hydronic systems, DEVI floor heating systems are truly maintenance free.
Is it possible for the heating cable to become faulty or burn out?
If the system is properly designed and installed, and it is controlled by a Devireg floor sensing thermostat, the cable will not be allowed to run hot enough to cause damage. Please refer to the 20 year warranty for further details.
If the heating cable is damaged can it be repaired?
Should a cable be damaged either during or after construction, the location can be detected using special testing equipment. Repairing a cable is normally straight forward and can usually be confined to a small area.
Does the heating cause structural damage such as cracking of the slab or tiles?
No. A properly designed floor heating system does not overheat the concrete or tiled surface. The concrete is typically heated to a maximum temperature in the range of 25°C to 45°C, much less than the temperature a concrete footpath would experience on a hot sunny day.
What value of home insulation is recommended?
We recommend that you provide for at least the minimum requirements as set out in the Building Code Australia. We also recommend the use of perimeter and under floor insulation to the slab itself, particularly in cold areas. The higher the levels of insulation, the lower the running costs.


How much does it cost to run electrical floor heating?
The cost depends on the size of the room, available floor space, and whether the system is to be used as the only heating source or as a warm floor. A 5m² bathroom with shower would normally requires 4 m² DEVImat™ and DEVIreg™ thermostat. Dimensioning of total heating requires contact to the DEVI partner in your local area. Electrical floor heating normally costs less in purchasing and installation than any other conventional heating system. The general rule is: the bigger installation area is, the lower the system price per square meter.

Bathroom Installations

Do I need to change the flooring when I want to install DEVI floor heating in my bathroom?
An easy and clean solution such as DEVImat™ gives you possibility to leave an old floor without removing it and creating unnecessary mess. The thought of broken up floors and craftsmen running in and out of the house used to be enough for most people to simply drop the idea of having their feet and floors heated. Today, there is no need to shiver when thinking about floor heating. You are able to get a warm floor without going through the expenses, dirt, and fuss of having to break up the old floor. The DEVImat™ is only between 2.3 mm and 4 mm thick, depending on type. It can therefore easily be fitted directly on to your existing floor, whether it is concrete, timber or even an old tiled or terrazzo surface, without needing to cut up the existing floor construction. The DEVImat™ is installed within the thickness of the tile adhesives and, therefore, adds no significant height to the floor level. Consequently, there should be no need to reduce door heights, raise skirting boards, etc.

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