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Cablewarm® Electric Underfloor Heating FAQs

Underfloor heating - how do I work out what I need?


Floor Heating have produced a comprehensive under floor heating Installation Guide to help answer all your questions; whether you are a first time DIYer, builder, electrician, tiler or experienced trade installer. You will find a wealth of information, useful tips and advice on measuring up and selecting your correct cable or mat for the job, graphical images on cutting and laying heating mats and siting and wiring your thermostat controller.

A range of our recommended flexible tiling adhesives and levelling compounds are also available to add to your order and can be viewed by clicking here

To help simplify your new underfloor heating installation, we have also provided a range of low cost tools to complete the job and can be viewed on the website by clicking here.

Electric under floor heating - what is Cablewarm®?


Cablewarm® underfloor heating cables are manufactured from multi-strand copper, twin heating conductors with a PTFE outer insulation, high tensile film screen, copper braid earth shield with a high temperature PVC (melt point 105°C) outer protective jacket; to form a twin conductor heating cable.

Cablewarm® underfloor heating cables are totally waterproof and incorporate an earth screen, making them perfectly suited for installations in wet areas.

The resulting heating cable is extremely safe, durable and robust, with a thin profile of 3.5mm.

What is the Cablewarm®150 Standard Output heating mat?


Cablewarm®150 heating cables are attached to a 500mm open weave mesh mat backing at 75mm preset factory spacing, to produce the Standard Output Cablewarm150® heating mats (150W/m²) and are ideally suited for the majority of underfloor heating applications.

What is the Cablewarm®200 High Output heating mat?


Cablewarm®200 heating cables are attached to a 500mm open weave mesh mat backing at 75mm preset factory spacing, designed to produce a High Output heating mat (200W/m²). Cablewarm200® heating mats should be used in primary heating applications for conservatories; areas of high heat loss, or where no additional thermal insulation is being installed: where a high heat output is required.

What is the difference between laying a single cable and a heating mat?


Variable output heating cables are designed for installations where a higher degree of flexibilty is required for complicated floor areas. Heating cables are suitable for use over both concrete or wood sub-floors.

Cablewarm® heating mats consist of a single cable manufactured on to a glass fibre mat backing with a factory set spacing to achieve a consistent output of either 150 or 200 watts per m². All Cablewarm® heating mats are manufactured with protective sticky backing strips on the underside of the mat, allowing the installer to roll the mat out, peeling the protective layer to expose the sticky surface to secure the mat to the sub-floor.

Heating mats are the ideal solution to getting rapid floor coverage but retaining the flexibility of installation. The mat backing can be cut to manoeuvre the mat roll around obstacles; the cable can also be removed from the mat backing, allowing more flexibility to give maximum coverage over the floor.

When would you use a loose heated cable instead of a heated cable mat?


For small or complicated areas like bathrooms: a single heating cable is the answer but where larger areas are concerned underfloor heating mats are the ideal solution. A single heating cable will require an even spacing and taping down onto the heating insulation or sub-floor to hold in place prior to tiling.

For larger, more straightforward areas: Cablewarm® electric underfloor heating mats are the professionals' choice, pre-spaced and fast to lay; for more info on how to lay Cablewarm® heating mats click here. Tiling can commence straight away without the need to set the correct spacing or be concerned the spacings could be inadvertently altered before floor tiling was complete.

What if I have a large area to heat?


Larger installations are usually a combination of 2 or more underfloor heating mats or cables wired in parallel up to a maximum of 3,680 watts or 16 amps.

Alternatively, for areas in excess of the above or where only a single thermostat is required for large areas, a contactor can be used; this will control up to a maximum of 22K/w (22,000 watts) of heating mats/cables or 96 amps loading.

How do I work out what underfloor heating cable or heating mat size I need for my project?


To assist you in selecting the correct size cables/mats for your installation, Floor Heating has produced a Sizing Guide for each Cablewarm® product. From the area you plan to heat, deduct approximately 10% and select the nearest Cablewarm® heating cable/mat down from that in the Cablewarm® range. 

To control your underfloor heating system, a choice of market leading brands of fully programmable, digital thermostats are available from the Floor Heating range; be sure to select the appropriate ampage product to suit your heating mats/cables.

What is the advantage of a 200 watts per m² underfloor heating mat?


Cablewarm®200 heating mats should be used in primary heating applications for conservatories areas of high heat loss or where no additional thermal insulation is being installed, where a high heat output is required.

Can Cablewarm® under floor heating cables be cut to length if too long?


Under no circumstances can underfloor heating cables be cut to length.

For single heating cables the floor spacing pitch can be adjusted closer together down to a minimum of 50mm, this will result in a higher wattage output per m².

If under floor cable heating mats are too long select the nearest heating mat down from within the Cablewarm® range.

What can I do if I have made a mistake and ordered a Cablewarm® heating mat that is too long?


If in any doubt always work out how many widths of 500mm will be required to fill the area of the floor you intend to heat. Simulate the number of times you will need to cover the area by rolling the heating mat out back and forth and measure.
Provided you have not cut any part of the heating mat we will give you a full refund against a smaller heating mat.

How quickly can I expect my tiled floor to get warm with Cablewarm® heating mats?


This depends on a number of factors, like the sub-floor type and insulation: a cement sub-floor will be slow to warm without a thermal insulation barrier, creating a significant drag on the performance of the floor heating. A layer of high quality insulation will have a dramatic effect in these circumstances, speeding up the initial warm up times to within 15-20 minutes. We recommend the use of Fastwarm® underfloor heating thermal insulation - for more info on Fastwarm® floor insulation click here.

Will electric underfloor heating also warm my room?


This will depend on the U Value of your room. U Value is an industry term for the total measure of resistance of each component that makes up the fabric of the building. Simply put, this means that old buildings will lose heat faster than modern buildings where the latest materials are incorporated. Under floor heating insulation will go a long way towards offsetting these drawbacks, helping to retain the heat within the room.

Underfloor heating acts like a large, low level radiator gently heating the room from the feet up, this requires approximately 15% less energy to feel the same level of comfort experienced using convection heating.

Will electric underfloor heating provide enough heat for my conservatory?


With a good level of floor insulation and the correct choice of floor heating mats/cables to get the maximum coverage and output, then in most circumstances under floor heating will provide the required room temperature.

Most conservatories are not required to pass any building regulation U Values, so depending on the type of glass structure you have, supplemental heating may be required for odd occasions like cold winter nights.

Can I adjust the temperature of the floor heating mats?


Each under floor heating installation is controlled by a programmable, digital thermostat. This will maintain your floor temperature and on/off times at a precise setting according to your own individual lifestyle choices.

How can I control the under floor heating to come on and go off?


Each installation is thermostatically controlled using a digital interface and floor sensor to monitor the underfloor heating system within 1° C of your temperature settings. A thermostat can be selected to control either the floor only temperature (comfort heating) or the ambient, room and floor (primary heating) temperature.

All thermosats have 4 on/off settings within any 24 hour period, allowing complete control of the floor heating to suit your lifestyle and come with either a 2 or 3 year manufacturer's guarantee.

Are there any special tools required for the underfloor heating installation?


Tiling over under floor heating cables should always be done using a plastic trowel. Any damage by the the sharp edge of a traditional steel trowel may result in damage to the outer, protective jacket of the under tile heating cable, this could eventually result in a future failure of the under floor heating cable.

To test the under floor heating system is correctly installed you will also require an Ohmmeter or Multimeter to take a resistance reading, prior to commencing tiling.

Do I need to be an expert to install the under floor heating system?


All Cablewarm® heating mats come with a full set of installation instructions. Most small to medium size underfloor heating systems can be installed on a DIY basis but it is recommended that a fully qualified electrician be consulted beforehand to advise and connect the electric underfloor heating system to an electric supply via an RCD and fused spur.

Larger areas will need careful planning due to the extra electricity loading calculations that will be required, a separate power supply may be needed for large under floor cable heating installations.

How do I connect the under floor cable heating mats to the household power supply?


It is highly recommended that you connect your under floor cable heating system via a fused spur (to isolate the heating system for future maintenance). The power supply should be from a safety contact breaker (RCD) to the thermostat, an electrician will be able to advise you.

Will I need an electrician to connect the under floor heating mat installation?


In accordance with current Part P domestic electrical conections, we strongly recommend a fully qualified electrician to check out your electrical underfloor heating system and to advise accordingly.

Is there any special adhesive I need to use when fitting an under floor cable heating system?


Yes, a flexible floor tile adhesive will be required. The special polymers added to flexible adhesives will make allowances for any tile floor movements through heat expansion and contraction - don't forget to also add a flexible grout to your list.

Can I tile straight on top of the cable heating mats?


For single, loose laid underfloor cable heating systems it is usual to pour a leveling compound screed over the floor area to the depth of the heating cables, to fix and fully encapsulate the heating cable; tiling can commence as a separate operation.

For heated cable mats the heating cables are secure within the heating mat backing, the tiler can commence with the flexible floor tile adhesive and tiling operation as soon as the under floor cable heating system is fitted.

What extra height will the under floor cable heating mat add to my floor?


This will depend on the size of the cable heating mat but an allowance of an extra 4 mm to your planned finished height is a reasonable figure.

What guarantee comes with the under floor cable heating mats?


All Cablewarm® underfloor cable heating systems come with a 10 year manufacturer's guarantee.

Can I lay under floor cable heating mats under wood laminate flooring?


This is possible but there are a number of extra steps involved. All underfloor heating cables require fully encapsulating. The application of a flexible leveling compound screed to a recommended depth of 6-7mm is necessary to cover the heating cable/mat in preparation to laying the laminate flooring.

Can I install the underfloor cable heating mats without insulation?


Yes this is entirely possible but the laws of science state that heat will always be attracted towards cold: heat energy will dissipate into the sub-floor, requiring more heat energy to bring the heated floor up to temperature.

If no insulation can be accomodated due to the additional floor makeup, then it is recommended that the High Output Cablewarm®200 heating mat is selected.

How will insulation improve the performance of my Cablewarm® under floor cable heating?


A high quality thermal barrier will slow the process of heat loss into the sub-floor, significantly improving the performance, speeding the initial warm up times and reducing the electricity costs. We recommend Faswarm® under floor heating insulation.

What type of under floor heating insulation will give me the best all round performance?


Extruded polystyrene foams will give the best all round performance. Polystyrene has high thermal insulation properties, high compressive strength capable of supporting normal foot traffic impact loading, waterproof, rot resistant, light weight, easy to handle, easily cut and shaped with a sharp knife, available in various depths from 6mm to 60mm and low cost. We recommend Faswarm® under floor heating insulation.

Do I need underfloor heating insulation with a reflective surface?


Reflective surfaces will give a greater performance when an air barrier is present (like behind a radiator). If buried within a cement layer then the reflective surface will now act as a conductor and transfer heat or cold. No useful gain can be attributed to a reflective surface when applied in this way.

Isn't underfloor heating insulation expensive?


Yes, under floor heating insulation can be expensive if choosing tile backer boards as insulation. These boards are manufactured with a reinforcing cementitious face to give them extra rigidity when used as a wall and are perfectly suited as waterproof walls to tile on in wet areas. For heated floors however, this extra cementitious layer is entirely unnecessary and will not add any extra strength to the board.

What is Fastwarm® underfloor heating insulation?


Fastwarm® underfloor heating insulation boards are manufactured from extruded polystyrene foam, designed to meet the very specific needs of the under-floor heating industry.

How strong are Fastwarm® underfloor heating insulation boards?


Fastwarm® under floor heating insulation boards are designed to meet the very rigorous needs to be both high thermal value and high compressive strength, capable of normal foot traffic point loading.

What depth of under floor heating insulation do I need?


A simple rule of thumb is to incorporate as much heating insulation wherever possible. For new build projects this is easy to plan but in a typical refurbish situation this is not always possible where the finished heated floor height may restrict the depth available to add the heating insulation.

Fastwarm under floor heating insulation boards are available from 6mm to 60mm.

How do I fix Fastwarm® under floor heating insulation boards to the sub-floor?


For cement sub-floors Fastwarm® under floor heating insulation boards will readily bond to any good quality flexible, water based (solvent-free) floor tile adhesive.

For heated wood floors care must be taken to ensure that the floor is firmly fixed to the joists, following the recommended 300mm screwed centres as a guide, prior to applying the flexible floor tile adhesive and bonding the Fastwarm® insulation boards.

I don't plan to heat all the floor so can I tile straight on to Fastwarm® under floor heating insulation boards?


Yes, following on from the question above continue with the same flexible floor tile adhesive laying tiles in the normal way.
Even without under-floor heating the tiled floor will be warmer as a result.

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