Underfloor Heating Buying Guide

Electric underfloor heating systems are comprised of a roll of cable spaced out beneath the floor covering. As the cables heat up, the floor radiates heat up into the room.

Advantages

Electric underfloor heating is usually cheaper to install than wet underfloor heating. It can be fitted directly on top of your existing flooring, with nothing more than a layer of insulation beneath to capture the heat. Many of the initial stages of installation can even be tackled DIY, although you’ll always need a qualified electrician to hardwire the system into the mains and wire your thermostat. Electric underfloor heating cable can be as little as 2mm thick, so your system will only raise floor heights to a minimal degree. For both these reasons, electric underfloor heating is the most popular choice for retro-fitting projects.

Electric systems usually heat up faster than water systems. They are maintenance free and do not require you to balance the hot water supply from your boiler. Electronic thermostats offer precision control of your floor and room temperature, helping you to manage your system more efficiently. If you are looking at heating an eco-home, electric underfloor heating can be a suitable option powered by electricity generated from wind turbines or solar panels.

Disadvantages

Electric underfloor heating has many advantages, but does share some disadvantages with other types of electric heating. Electricity is usually more expensive than gas, so running costs of electric underfloor heating tend to be higher than water underfloor heating. These costs may or may not be balanced out by the relative cheapness of installing electric underfloor heating. Electricity generally works out cheaper overall in retro-fitting projects, or in well-insulated locations that only require low levels of heat to maintain comfort temperatures.

Another drawback to electric underfloor heating is that it will not work if there is a power cut.

Water underfloor heating systems are comprised of a system of pipes. As hot water flows through the pipes, the floor heats up and radiates heat into the room.

Advantages

Like central heating, water underfloor heating systems are powered by your boiler. This means you can take advantage of the cheaper cost of oil or gas over electricity; water underfloor heating systems are usually cheaper to run than electric underfloor heating systems. You’ll also avoid the risk of losing your heating because of a power cut.

Water underfloor heating systems can be effectively paired with a ground source or air source heat pump to provide an eco-friendly heating solution.

Disadvantages

Water underfloor heating systems are more expensive to install than electric systems. Ideally, the pipes will be recessed into the floor, either between the joists if you have a wooden sub-floor, or set in screed if you have a concrete sub-floor. This is a time-consuming and disruptive process in an existing house because you will need to refit your subfloor. Retro-fitting systems are available, however, because heating pipes are thicker than heating cables, these systems will raise your floor level by a considerable amount. It is usually only economical and practical to fit water underfloor heating in a new build, where you can take advantage of a “clean slate” for installation. In new build projects, the cheaper running costs of water underfloor heating will outweigh the initial cost of installation.

Another disadvantage to the more “integrated” installation of water underfloor heating is that the system is difficult to access in the event of a problem. Water underfloor systems also heat up slower than electric systems, and are difficult to install in upstairs rooms. You will also need to factor into your budget the cost of having your boiler maintained and serviced every year.

To get the most out of a tile, stone or concrete floor, we recommend choosing floor coverings with a maximum thickness of 20mm. Thicker stone floor coverings will not reduce the heat output but they will take longer to heat up. Popular choices include ceramic tiles, stone tiles, polished screed, slate, flagstone and marble.

Many types of vinyl, rubber and linoleum floor coverings are suitable for use with underfloor heating, however you should always check with the manufacturer before fitting.

The most effective wooden floor coverings are those which are thinnest and most dense. Thin wooden floors will heat up faster than thicker wooden floors, whilst dense wooden floors will conduct heat more effectively than porous wooden floors which effectively insulate the heat with pockets of trapped air. As a general rule, you should look for wooden floor coverings that are no more than 18mm thick. Engineered timber and kiln dried floors typically make the best pairing with underfloor heating because they adapt well to changes in temperature. Solid wood floors are usually unsuitable because they are very sensitive to changes in temperature and humidity; they are also more likely to act as an insulator, because they are typically thick and not very dense.

Such is the range and diversity of wooden floor coverings available that you should always defer to the manufacturer’s guidelines regarding installation instructions and suitability for use with underfloor heating.

Carpeted floors should not be heated beyond 27 °C, so should only be used with systems of 150w/m² or less, unless fitted with a temperature-limiting thermostat. It is also important to ensure that the carpet, underlay and any overlays required for your installation do not exceed a combined tog rating of 2.5 tog. A combined tog rating of more than 2.5 tog will insulate your system to the extent that it will not be able to provide a sufficient heat output.

Always check with the manufacturer before purchasing a carpet for use with your underfloor heating system.

Foil mat heating systems should not be used with these floor types because tile adhesive, screed and concrete will not adhere to the foil matting.

However, it is possible to use wood, laminate, carpet and vinyl floor coverings with a sticky mat or loose cable system. The main reason for doing this is to futureproof your system. Tile and stone floors cannot be used with foil mat systems, so if you want the option of a tiled floor in future, you should choose a loose wire or sticky mat system. You will need to use a layer of self-levelling compound at least 10mm deep before fitting a wood, laminate, carpet or vinyl floor on a loose wire or sticky mat system.

Loose wire kits offer the most flexibility of all the underfloor heating systems. The cables are easy to fit around small spaces and awkward items of furniture such as basins and toilets. This makes them particularly popular in small rooms and bathrooms. Loose wire kits are easy to retro-fit over existing floors, and can be used beneath all major floor coverings – including tiled, stone, vinyl, carpet, wood and laminate floors.

Like other retro-fitting options, a loose wire kit will raise your floor height somewhat, but this will only be a matter of millimetres. The main disadvantage of loose wire systems is that they can be time consuming to install. The cables must be spaced out and taped down by hand, which takes longer than mat systems which simply unroll over the floor.

Sticky mats can be installed much faster than loose wire systems. All you have to do is unroll the mats over the floor, cutting the netting when you reach the wall so you can flip the mat and continue unrolling in the opposite direction. You must never cut the cables. Sticky mats are suitable for use with all major floor covering types, including tiled, stone, wood, laminate, carpet and vinyl floors.

Like all retro-fitting options, sticky mats will raise your floor height by a few millimetres. Whilst sticky mats are faster and easier to install in large, square rooms, you may find the flexibility offered by loose wire kits more practical when installing underfloor heating in a small or awkwardly shaped room.

Foil mats are the easiest underfloor heating system to install. Like sticky mats, they simply unroll over the floor. Unlike sticky mats, however, they do not require any adhesive layers; wood and laminate floors can be laid directly over the foil, whilst carpet and vinyl floors need only an intermediary layer of MDF overlay to protect the heating cables. Foil mats are the best system to choose if you want a fast and easy installation that’s possible to undertake as a DIY project. However, you will still need the help of a qualified electrician to connect your system to the mains and wire your thermostat.

The main drawback to foil mat systems is that they cannot be used with tile or stone floor coverings. This is because adhesive layers such as tile adhesive, self-levelling compound and screed will not adhere to the foil surface. We don’t recommend choosing a foil mat system if you think you may want a tile or stone floor covering in the future. Loose wire and sticky mat systems are the futureproof choice; they can be used with carpet, vinyl, wood and laminate floor coverings as long as a 10mm layer of self-levelling compound is used on top of the cables.

Like all retro-fitting underfloor heating systems, foil mats will raise your floor height by a matter of millimetres. It’s also worth noting that the MDF layer required when fitting carpet or vinyl floor coverings over a foil mat is not waterproof. For this reason, we do not recommend foil mat underfloor heating in a carpeted or vinyl-floored bathroom.

The main advantage of in screed cables is that they do not raise overall floor heights. They can also be used with all major types of floor covering, including tiled, stone, carpet, vinyl, wood and laminate floors.

However, the installation process for in screed cables is tricky and time consuming. It is best left to the professionals, and is usually only a practical option in new build properties.

If you just want to keep your floor warm, a low wattage system will be adequate. Look out for heating mats and cable kits with wattages from 100w/m² to 130w/m².

If you want to use underfloor heating as your primary room heating source, you will need to choose a system with a wattage sufficient to warm the entire space. To do this, you will need to consider the rate of heat loss from the room.

As a general rule, a system of 140w/m² to 150w/m² should be adequate for a room with a standard rate of heat loss.

Rooms with a high rate of heat loss will require a higher wattage system to ensure temperatures can be maintained. Wattage kits of 190w/m² to 200w/m² are recommended for rooms which are poorly insulated – such as period properties, conservatories and garage conversions – and rooms which have a high volume to heat, such as high-ceilinged rooms, hallways and multi-storey spaces.

It may also be advantageous to use a 200w/m² system in rooms such as kitchens which have a lot of floor space taken up by fixed furnishings. This is because your heating area will be much smaller than the overall area of the room you are trying to heat. If more than 20% of your floor surface area is taken up by fixed furniture, you should be considering a 200w/m² heating system.

It goes without saying that high wattage systems are more expensive than lower wattages, because you will be using more cable to heat the same sized space.

Only tile and stone floor coverings can be heated to the level required in areas of high heat loss. For this reason, we always recommend choosing a tile or stone floor finish for conservatories, garage conversions, and other high wattage environments that need a 200w/m² kit for comfortable heating.

Most wood, laminate, carpet and vinyl floor coverings are subject to a 27 °C temperature limit to prevent damage. This can be achieved with a 140w/m² to 150w/m² kit and is sufficient for comfort heating in rooms with standard levels of insulation. However, this may not be hot enough if your room has a high rate of heat loss. You can still use a high wattage system with these floor coverings if you want to take advantage of their faster heat up times, but you must use the thermostat to restrict the floor temperature, which means the room will not get warmer overall.

We always recommend checking the temperature limit of your floor covering with the manufacturer before choosing an underfloor heating system.

Calculating your heated floor area is simply a matter of subtracting the area of any fixed or permanent room furnishings from your total room area. We then recommend taking a further 10% off your total, to ensure you do not purchase a heating system which is too large. We’ve made this even easier with our room area calculator.

It is very important that you do not order an underfloor heating kit which is too large, because the wires cannot be cut.

If you prefer, you can send the details of your installation to our sales team who will happily send you a free quote.

Permanent furnishings with a solid base will obstruct the heat output of your underfloor heating. This wastes energy, does nothing to warm your room and can also damage the cables over time.

Examples of permanent fixtures and solid furnishings which you should plan around include kitchen units, washing machines, fridges, shelving units, cabinets and sofas. You may also wish to plan around smaller, semi-permanent items of furniture which nevertheless cover a significant amount of floor space: dog beds, washing baskets and storage boxes are good examples. We do not recommend using rugs in rooms with underfloor heating.

You can, however, fit underfloor heating beneath larger items of furniture that have plenty of clearance from the floor. Tables, chairs and raised desks can all be positioned over underfloor heating systems because they allow plenty of room for the heat to radiate from the floor and circulate around the rest of the room.

If more than 20% of your floor space is excluded from your heating plan, you may wish to consider a 200w/m² heating system to ensure your system can keep the entire room at a comfortable temperature. 200w/m² systems will only be effective if used with tiled or stone floor coverings.

We sell our underfloor heating cables and mats in pre-assembled packages for set floor areas. Simply click on the product of your choice and choose your heated area from the dropdown menu.

If we do not stock a package just right for your room size, you may need to combine heaters to make up your floor area. For instance, to heat a 9m² room with our Warmup sticky mats, you will need to use a 4m² and 5m² sticky mat system. Combining floor area packages in this fashion is fairly intuitive. However, for clarity, you will find a chart showing recommended combinations for selected floor areas on every product page.

Remember, it’s always wise to choose a heating system which is slightly smaller than your heated area, rather than larger. Cables can be rearranged to fit a larger area, but they cannot be cut to fit a smaller area. If your area falls between two available sizes, always go for the smaller size – do not be tempted to round up!

Even if you are retro-fitting your underfloor heating over an existing, already insulated floor level, it is still important to fit your heating with a new layer of insulation. This is because your old floor covering will act as a conductor, allowing heat to escape downwards until it reaches your in-situ insulation. With a new layer of insulation in place, all this heat will be directed upwards, into the room.

Insulation can also serve a number of other purposes, depending on what type of underfloor system you’re planning to install. Soft insulation boards provide cushioning to foil mat systems, whilst cement coated insulation boards provide support to tiled floor coverings. You can also use suitable insulation boards for waterproofing and soundproofing.

To make this easier for you, we’ve specified on every product page what type of insulation board you need, depending on your sub-floor. We’ve even added calculators to show you how much you’ll need, so you can add the boards to your basket there and then. But if you’re interested in why you need certain boards for certain projects – read on!

Insulation boards vary in several ways, including: density, rigidity, solidity, thickness, the level of sound-proofing they offer, whether or not they are waterproof, and whether or not they have a cement coating.

Coated vs Uncoated

The most important thing to check when choosing your boards is whether the boards need to be coated and whether they need to be dense.

Coated boards are necessary whenever a firm, level surface is required – for example when under-tile systems are used on top of a timber substrate. Conversely, uncoated boards may be required if your heating system needs cushioning to prevent damage – for example when a foil heater is used directly under wooden flooring.

Uncoated boards vary in their density. Dense boards are better insulators and can be stuck down with a suitable adhesive. They are the best choice for installations that don’t require a coated board but do require boards that can be fixed to the substrate – for example, under-tile systems over a concrete substrate. Dense boards can also be used without adhesive with foil heating mats if you want to take advantage of their superior insulative properties. Less dense boards are cheaper, but are less insulative and too spongy to be used with adhesive. This means they are only suitable for use under foil heating mats.

Confused? You can check what sort of boards are needed for your heating system using the table below.

Thickness

You will find that some boards are available in different thicknesses. Choosing the thickness of your insulation is always a trade-off between making your system more efficient and minimising the degree to which your floor level is raised. The thicker your insulation, the faster your system will heat up and the more efficient it will be. As a general rule, all underfloor heating installations should have a minimum of 5mm insulation between the sub-floor and the heating system.

R Value

An easy way to compare the level of insulation offered by competing boards is to check the boards’ R Values. R Values measure the level of thermal resistance offered by the boards. The higher the number, the higher the quality of insulation.

Insulation boards are sold in packs by floor area coverage, so, in theory, it is quite easy to work out exactly how many boards you will need to cover a certain size area. However, in practice, you will find that you need several more boards than the total required to make up your surface area. This is because boards will have to be cut and rearranged to suit the exact shape of your room and fit around any awkward fixtures.

The board calculator takes this into account, ensuring the number of boards you order will be sufficient to insulate your entire room – no matter how awkward the shape.

The job of the thermostat is to measure and maintain temperatures. Underfloor heating thermostats are unique in that they measure the floor temperature as well as the room temperature. This allows you to set a maximum temperature for your floor. This is essential for safety, ensuring you never overheat your floors and risk damage to the system. This also allows you to lay temperature-restricted floor coverings such as wood, carpet and linoleum, safe in the knowledge that your heating system will not exceed the standard limit of 27 °C.

The thermostat is your main point of control over your underfloor heating system, so it’s important you choose a model which offers the level of control you require to run your system efficiently and conveniently.

Most thermostats are limited to two input cables and a maximum load of 16 Amps. In standard UK 230V systems, this equates to a limit of just over 3600W.

You can check the total wattage of your chosen underfloor heating system by looking in the product specification. However, as a general rule, a 16 Amp thermostat will be sufficient for the following room areas, depending on what wattage system you are using:

If your underfloor heating system is made up of more than two separate heating mats or cables, your electrician may need to use a junction box to wire all the cables into the thermostat.

If your underfloor heating system exceeds the thermostat’s maximum load, it is possible for your electrician to use a contactor to switch the load. However, you should consider at this point whether it would be more advantageous to install a second thermostat. Large rooms and multi-room setups may have localised hot and cold spots, so a single thermostat may no longer give a representative reading for the entire space.

We recommend seeking the advice of your electrician before choosing a location for your thermostat. The most sensible location for your thermostat will depend on the layout of your existing wiring, although it should be possible for your electrician to connect your thermostat to the mains from any position in the room.

Pre-existing wall mounted controllers will give a good indication of the best place to fit your thermostat. Most thermostats use the same basic wiring, so replacing an obsolete wall mounted controller with your underfloor heating thermostat would be a quick and easy job for any electrician.

If you are installing underfloor heating in a bathroom or wet room, the thermostat should be mounted in the next dry room – usually the hallway.

Here are some of the features to look out for when making your choice:

Manual or Digital

Manual thermostats offer rudimentary heating control with a traditional-style dial to adjust the temperature. Manual thermostats are easy to use but give you limited control over your heating. Most manual controllers give you basic on/off on-demand control and do not allow you to program your heating.

Digital thermostats are more accurate than manual thermostats and offer a greater degree of control. They typically sport more modern designs, with LCD or touchscreen displays. Most digital thermostats allow you to program your heating, and may well offer a raft of additional smart features.

It’s true to say that not all digital thermostats are equally easy to use. Older digital thermostats sometimes suffer from unintuitive interfaces which are difficult to use without consulting the manual. However, the most up-to-date digital thermostats have been carefully designed to optimise ease-of-use: employing sliders, touchscreens, Wi-Fi control and everyday language to make programming as intuitive as possible. A good digital thermostat will be as easy to use as a manual thermostat.

Programming

Programming your underfloor heating is an easy way to reduce your energy usage without compromising your comfort. When you program your heating, it will follow your personalised schedule automatically, switching on and off and changing temperature according to your needs. Your house will be warm when you wake up in the morning and get in from work, without wasting energy heating overnight, or when the house is empty.

The level of programming offered will vary between models. The most sophisticated thermostats will offer a range of pre-set programs as well as several customisable programs. They will allow you to set a different heating mode for every half-hour interval of every day of the week, and you will be able to choose from a range of customisable heating modes, such as comfort, economy and anti-freeze.

Thermostats which do not offer programming will work on a simple off/on, on-demand basis. This may be suitable for rooms you use on an occasional basis, such as workshops or conservatories, but is not recommended for your primary living spaces.

Wi-Fi Control

Thermostats with Wi-Fi control allow you to control your underfloor heating from anywhere in the world, provided you can connect to the internet. This is a very convenient feature which allows you to make adjustments to your heating while you’re at work, away on holiday, on public transport, or, indeed, sat comfortably on the sofa unwilling to get up and walk to the thermostat!

Wi-Fi controllable thermostats wire into the mains and connect to your underfloor heating in the same way as a regular thermostat. The thermostat will then connect to your Wi-Fi network in the same way as a phone or laptop. You will be able to control the thermostat by downloading the manufacturer’s app onto your device or creating an account on the manufacturer’s website.

Note that although Wi-Fi controllable thermostats are commonly referred to as “wireless”, they are only wireless in the way they communicate with mobile devices and laptops. They must be fully wired into both the mains and your underfloor heating system.

Design

Your thermostat needn’t be an eyesore. We sell thermostats in a wide range of colours with something to suit most interior design schemes. Our most sophisticated touchscreen thermostats come with customisable displays that allow you to change the colour scheme or even upload a personal photo as your backdrop, so there are plenty of ways to make sure your thermostat fits into your interior design.

Smart Features

These days, heating thermostats are more than simple temperature limiters. Today, underfloor heating thermostats are available with a raft of intelligent features designed to do everything from measuring your energy usage to checking the weather. Here are some of the best to look out for:

Energy Monitor

Thermostats with an energy monitor will record your energy usage, calculate running costs and generate graphs which show you how and when you use energy.

Learning Mode

Thermostats with learning mode work continuously to optimise your heating, adjusting heat output and programming to ensure comfortable heating is always provided as efficiently as possible. This can work on both a long term and a short term basis.

In the short term, the thermostat will adjust its heat output to compensate for changes in the immediate environment. These adjustments can range from switching off the heating when an open window is sensed, to programming the heating to switch on earlier when colder weather is forecast.

In the long term, your thermostat will learn how you like to use your heating and will adjust your schedule to find the most efficient way of warming the room to your preferences.

Tariff Switching

Tariff switching thermostats monitor your energy usage and keep a constant eye on the energy market to make sure you’re on the best value tariff. The thermostat will notify you if it finds a more competitive tariff – or you can set it to switch automatically.

Energy Saving Advice

The thermostat will analyse your energy usage and generate energy saving tips and advice specially tailored to your habits.

Additional Apps

You needn’t limit your thermostat to just controlling your heating. Why not choose a thermostat with additional apps and make it the central information hub for your home? Our smartest thermostats give you scope to download a wide range of handy, non-heating-related apps onto your thermostat. These might include weather forecasting, an outdoor temperature display, and even traffic reports tailored to your morning commute.

Fitting your heating mats or cables is the easiest part of the installation process. If you are using mats, all you have to do is unroll the mats over the floor, cutting the mesh or foil and turning the mat whenever you need to go around a corner. If you are using loose cables, the process is more time consuming but not difficult. You will need to lay the cables out with the spacing prescribed for the wattage you want to achieve, taping the cables down as you go. This process requires more patience than skill, and is entirely suitable for home developers with the most basic levels of DIY experience.

What is required above and below your heating mats or cables will depend on three main factors: the sub-floor onto which the heating system will be installed, the insulation you need between the substrate and the heating system, and the floor covering you want to use on top.

Foil mat heaters are the easiest system to install DIY because they never require any adhesive layers: the floor covering simply lies on top of the foil, with an intermediary layer of MDF if you’re fitting a carpet or vinyl floor. Sticky mat and loose wire systems require a little more care, because you will need to work with either tile adhesive or levelling compound.

Some floor coverings may be more difficult to install, so, depending on your level of DIY experience and the advice of the floor covering manufacturer, you may prefer to have this top layer fitted by a professional.
Typically, you should be able to complete about 90% of the installation process DIY.

The installation build-up above and below your heating system will vary depending on your sub-floor, your floor covering, and the type of heating system you are using. Full installation instructions can be found in our product manuals and installation videos – however, to help you compare your options, we’ve summarised the main installation configurations below.

Sticky Mats & Loose Wire Kits

Sub Floor

If you’re installing a sticky mat or loose wire system on a wooden floor, you will need to use cement coated boards to provide a firm base for your tiles or any layers of self-levelling compound. Cement coated boards should be fixed to the floor with screws and washers.

If you’re installing a sticky mat or loose wire system on a concrete floor, you can use dense uncoated boards because your system already has a firm base. The boards should be bonded to the substrate with a layer of flexible tile adhesive.

Floor Covering

If you’re installing tiles or stone flagging over your sticky mat or loose wire system, you can apply tile adhesive straight over the heating system and fit your tiles above. Some installers prefer to lay an intermediary layer of self-levelling compound before fitting tiles. This can make laying the floor covering easier because it gives you a flat surface to work with.

If you want to use any other floor covering with your sticky mat or loose wire heating system, you will first need to lay a 10mm layer of levelling compound over the cables. This protects the cables from either the grinding pressure of wood and laminate floors, or the risk of penetration through soft floor coverings such as carpet or vinyl. Please be aware if fitting carpet that the combined tog rating of the carpet and underlay should not exceed 2.5 tog.

Foil Mats

All foil mats require a soft layer of uncoated insulation between the substrate and the mat. This cushions the cables in the mat and offsets the pressure from the floor covering, preventing damage. Foil mat insulation is available as boards or as a roll, and does not need to be adhered to the substrate; it can simply be lain beneath the heating mat.

Floor Covering

Laminate and wood floor coverings can simply be lain over the foil mat.

Carpet and vinyl floor coverings will need an additional layer of MDF dual overlay on top of the foil to protect the heating cables from damage. The MDF layer does not need to be fixed down – it can simply be lain over the foil mat. Please note that if fitting a carpet, the combined tog rating of the carpet and underlay should not exceed 2.5 tog.

Tile and stone floor coverings are not suitable for use with foil mats.

It is important to use flexible tile adhesive for any application involved with underfloor heating. This is because changing temperatures will cause the adhesive to expand and contract, which would cause a standard tile adhesive to crack and damage your floor covering. Only flexible tile adhesives can withstand the changing temperatures generated by underfloor heating systems. Always check that your chosen tile adhesive is suitable for use with underfloor heating.

Tile adhesives vary in a number of ways, including their flexibility, consistency, colour, resistance to frost, how long they take to dry, and the maximum thickness they can be laid as an adhesive bed. The right adhesive for your project will depend on your floor covering; we always recommend checking with the floor covering manufacturer before choosing a tile adhesive to use with your tiles.

Tile adhesive is sold in bags as a dry powder and must be combined with water to form a workable mortar. All floor surfaces and insulation boards should be primed before they are bonded with tile adhesive. Priming ensures all surfaces are as smooth as possible, strengthening the adhesive’s bond with the substrate. It’s important to use a notched trowel when laying tile adhesive. Notched trowels ensure you lay your adhesive with suitably sized ridges, and prevent you using too much adhesive. An excess of adhesive can ooze up between the tiles and may allow your tiles to move. The tile adhesive will specify what size trowel to use when laying. Tile adhesive used for floor coverings must be left to dry for a minimum of 7 days before you switch on your underfloor heating.

The amount of tile adhesive you need for your installation will depend on your floor area and the depth of your adhesive beds. Typically, you will need a depth of around 3mm to bond insulation boards to your subfloor, with a layer of around 5mm required to tile over your cables. However, full instructions should be found in the manual of your chosen heating product.

You should never use more than 10mm of adhesive beneath your floor covering because this will insulate your heating system and allow less heat to rise into the room.

It is important to use a flexible levelling compound for all underfloor heating applications. This is because the compound must be able to withstand the changes in temperature generated by the underfloor heating system. Standard levelling compounds can crack when used with underfloor heating, which risks damage to both your floor covering and your heating system. Always choose a levelling compound which is advertised as suitable for use with underfloor heating.

Levelling compounds vary in a number of ways, including: strength, time taken to dry, ease of flow, suitability for use with different substrates, and the maximum depth which can be laid. The best levelling compound to use with your underfloor heating will depend on the substrate on which it will be laid. Check product specifications to ensure compatibility.

Levelling compounds are sold in bags as a dry powder and must be combined with water to form a free-flowing, homogenous mixture. Before laying, it is advisable to prime the substrate. This provides a smoother surface and increases the strength of the adhesive bond. The mixture can then be poured directly onto the substrate. You can use a solid bed trowel to create a smooth, level finish at the required thickness.

The required thickness of your layer of levelling compound will depend on your floor covering. A layer of 8-10mm is required if you want to fit carpet, vinyl, wood or laminate floor coverings over a sticky mat or loose wire heating system. A 5mm layer is recommended if you want to use the compound beneath tiles. Drying times vary greatly from one levelling compound to the next and can be found in the relevant product specification or manual.

Some primer brands developed specifically for use with underfloor heating will also boast of their insulative properties, helping to prevent heat loss through the floor. Whilst these primers may offer some benefits for the overall insulation of your system, this does not compare to the level of insulation provided by insulation boards or rolls; primer should be used in combination with, not instead of, insulation boards.

You will find a few different kinds of primer on the market. Make sure you choose a brand which is suitable for use with both your substrate and the tile adhesive or levelling compound you want to use on top. Full details of compatibility can be found on primer product pages.

Primer is easy to apply with a brush or roller and typically takes 1-2 hours to dry.

The amount of primer you will need will depend on the floor area of your project. You can check the coverage offered by different bottles of primer in their product specifications.

Dual overlay systems are fairly standard, with little variation between different products on the market. Note that when used with underfloor heating, dual overlay layers need to be thin to allow heat to pass efficiently through to the floor covering, so make sure your overlay system does not exceed a total of 7mm in thickness.

Installation is a quick and easy process that does not require the use of adhesives. It is important to lay the base layer first before laying the top layer above in a staggered, brick-like fashion. This prevents joints showing through your floor covering.

Note that dual overlay is not waterproof, so you should not use a foil heater combined with vinyl or carpet in a bathroom or wet room.

This means, in theory, that you have as much flexibility to choose your bathroom flooring as any other room in your house. Whilst ceramic, stone and vinyl tiles are the most popular choices, it’s also perfectly possible to have a wood or even a carpeted floor in your bathroom.

As such, the choices for bathroom underfloor heating are similarly open-ended. All underfloor heating systems have very high IP Ratings to protect against ingress from water, which is a risk in any room in the house – whether through spills, soggy feet or floor mopping. This means all our underfloor heating systems are safe to use in bathrooms. The main thing to consider is whether any of the layers required for installation will react badly to frequent exposure to water.

The only type of system you are likely to have a problem with is foil mats fitted beneath vinyl or carpet floors. These systems require a layer of MDF dual overlay to protect the cables. The dual overlay should not be exposed to water over long periods of time because it can warp and soften. If you’re in any doubt, plump for a loose wire or sticky mat system under a layer of self-levelling compound; this will allow you to fit carpet and vinyl floors without the layer of overlay.

The only floor coverings which you should use in wet rooms are those which are water-repellent and non-porous – namely, tiled or stone floor coverings. For this reason, only loose wire and sticky mat heating systems are suitable for use in wet rooms.

Your wet room will also require a tanking system fitted beneath your floor covering which seals up any gaps between your walls and floors and makes an impassable seal which delivers all the water down your drain. If you already have a tanking system in place, you can simply fit your cables over the top. However, if you’re starting the project from scratch, it’s worth looking out for underfloor heating kits which include a tanking system.

For example, our Vario Pro Loose Wire Heating Kit includes both a reel of underfloor cable and a roll of waterproof membrane designed to function as a tanking system. The membrane is unrolled over the floor, where it is fixed with tile adhesive, and any are gaps bridged with sealing compound and sealing tape. The underfloor heating cables then slot into the grooves of the membrane. This provides a waterproof, fully tanked heating system with a much lower build-up than an equivalent system built over an existing tanking system.

Thermostat wiring is not a DIY job. All aspects of underfloor heating wiring – including connecting the system and the thermostat to the mains – must be completed by a professional electrician.