Underfloor Heating - Frequently Asked Questions


How long will it take for the underfloor heating system to warm up?

The warm up time of an electric underfloor heating system will be dictated by the insulation used beneath it and the output of the system. In general, the better insulated the sub-floor the faster the system will warm up, with Heat Mat Underfloor Insulation boards facilitating a very speedy warm up time of as little as 15 minutes, and un-insulated concrete floors causing the slowest warm up time. Using a 200W system beneath ceramic/stone tiles provides a faster warm up time than 150W or 160W systems. We recommend using Thermal Underfloor Insulation boards wherever practical when installing Heat Mat systems onto concrete floors.


How much will it cost to run an electric underfloor heating system?

Although some people believe underfloor heating is expensive to run, the reality is that both the initial installation fee and the ongoing running costs can represent great value for money. The cost of running your system is based around many different factors so it is hard to generalise. It costs less than 10p to run 1m2 of underfloor heating at maximum power for 6 hours. However the running costs of a Heat Mat system will depend on: how well insulated the room is; the output and type of system; your energy tariff; the thermostat settings you choose.


Some suppliers offer electric underfloor heating which they claim to be 30-50% more efficient than ‘normal’ electric underfloor heating systems. Are they?

With any mains voltage electric heating system one kilowatt of electricity will produce one kilowatt of heat, whether it is a 3mm or 7mm cable or heating mats. With a low voltage system there is a small amount of wasted energy in the form of heat and noise within the transformer. The only things which significantly affect the cost of running one system compared to another are the insulation used beneath the system, the output of the system and the use of an intelligent thermostat. In general, the better the insulation used beneath it, and the higher output of the system, the cheaper it will be to run as long as it is used with an intelligent thermostat like Heat Mat’s NGT thermostat/timer.


I want to replace one of my old underfloor heating thermostats with a Heat Mat thermostat. Is this possible without taking up my floor to install a new floor sensor?

Yes, Heat Mats 4th generation NGT Thermostat and NG Touch are designed to be a straight swap with older thermostats, even those produced by other companies. Each brand’s floor sensor operates on a different Ohm rating, but our NGT thermostats are designed to take this into account.


What does a BEAB (British Electro-technical Approval Board) or VDE system approval mean?

This means that BEAB and VDE have independently verified and tested the heating mats with Heat Mat’s thermostats and they have confirmed that the system is safe and suitable for use as underfloor heating and that it complies with all necessary legislation. All of Heat Mat cables and thermostats are manufactured in BEAB approved factories. VDE (Association for electrical, electronic and information technologies)


Which is more expensive to run, 160W or 200W heating mats?

If the system is used with the thermostats adaptive function switched on then the 200W system will be slightly cheaper to use than the 160W system. This is due to the warm up time of the 200W system being slightly faster.


Can I turn my heating on the day it is fitted?

If you have installed your heating beneath tile adhesive, levelling compound or a screed you must allow this to dry out before turning on your system for the first time. If the system is turned on too early it will force the moisture out of the covering which may lead it to crack. We would recommend speaking to the manufacturer of your flexible tile adhesive, grout or screed to confirm the drying time required.


Are the heating systems connected in parallel or series?

The heating systems are always connected in parallel at the thermostat or in a connection box.


How do I install more than 14/16 Amps of underfloor heating?

If your chosen system exceeds the maximum Amp rating of your thermostat, you should consult with any one of our electricians who will be able to advise you on using a contactor to control the system.


Does each room require its own thermostat?

We would recommend that each room has its own heating system controlled by its own thermostat. This will allow for simpler and more accurate temperature control of each room and will avoid heating rooms which do not require it


Can the heating cable be shortened?

The heating cable cannot be shortened because each heating element has an adaptive resistance suitable for only one length of cable. If you shorten the cable it will not operate correctly.


I am uncertain of my final floor covering, what system should I install?

If you install 160W/sqm heating mats or 3mm cable beneath a levelling compound, or 7mm cable at 160W/m2 beneath a screed, virtually any floor covering can be laid on top.


Can I tile straight onto heating mats and 3mm cables?

You can tile straight onto heating mats and 3mm cables as long as you use a flexible tile adhesive and ensure that all of the heating cables are thoroughly covered. If installing a system in this way, the tiler should take particular care not to damage the heating cable when cleaning out grout line


If I damage a heating element can it be repaired?

Although the heating systems are very robust, accidents do happen! Luckily, it is very simple to repair all of Heat Mats heating elements (with the exception of the under laminate system element) if the damage is found before they are covered.


Can the heating system be repaired if it stops working, without taking the whole floor up?

On the very rare occasion that a system stops’ working once it has been covered all is not lost. Usually the problem is related to the electrical wiring or thermostat connections and if you speak to Heat Mat’s Technical Team they should be able to assist you in locating and correcting the error. If the fault appears to be located beneath a tiled floor or levelling compound, Heat Mat can provide the services of an independent engineer who specialises in locating and repairing damaged heating systems. The damaged area is located by using a thermal imaging camera and usually can be pinpointed to an area roughly the size of a ten pence piece. The engineer can then repair the cable beneath the floor by removing the minimum amount of tiles or compound. There is a charge for this service if the damage is found to have been caused subsequent to Heat Mat supplying the product.


If I need to drill a hole in the floor after my system has been laid, how do I miss the cables?

Although we do not recommend installing underfloor heating beneath areas where you will later need to drill into the floor, it does happen! Often a door stop needs to be installed or a pedestal requires screwing down and in these cases Heat Mat can supply Cable Trace film. Cable Trace film can locate 3mm heating cables and heating mats if they have been laid directly beneath tiled floors. You simply place the film on the cold floor and then turn the heating on, and the image of the cables will show up on the film.


What is a thermal block?

A thermal block is any layer of insulating material that is placed on top of an underfloor heating system that prevents the heat from leaving the floor. Thermal blocks include obvious items such as large beanbag furniture or a futon with no air gap beneath it but also include less obvious items such as rubber backed rugs or even a pile of newspapers. By preventing the heat from escaping the thermal block causes the floor beneath it to keep on heating up above its normal temperature and, unless the floor temperature sensor happens to be located beneath the thermal block, the heating system will not realise the heat is building up and will keep heating the floor. In extreme circumstances this can lead to the floor covering being damaged.


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