Guides|26 October 2020

Your Guide To Electric Underfloor Heating


Eoin McDaid-Digital Lead

During the last ten years the popularity in electric underfloor heating has risen significantly in the UK. Gone are the days that underfloor heating is considered an expensive luxury that’s just a ‘nice to have’, it is now considered one of the most efficient ways to heat the home.

It costs less than one average takeaway coffee to run 2m² of electric underfloor heating for one month.

No more fighting over the chair nearest the radiator, electric underfloor heating provides a perfectly even level of heat throughout any room.

Unlike conventional central heating systems which cause the warm air to rise, electric underfloor heating is designed to provide evenly distributed heat throughout a room. Once installed, electric underfloor heating requires very little maintenance and rooms benefit from reductions in drafts and airborne allergens.

If electric underfloor heating sounds like the ideal option for your project, it is likely you are wondering how it is installed, what systems best and how to measure up for it. Fear not, this guide has got you covered.

Chose a type of Electric Underfloor Heating:

When you are finishing your floor with either tile or stone, there are a two main types of electric underfloor heating to choose from, ThermoSphere Membrane or ThermoSphere Mesh.

Thermosphere Mesh are electric underfloor heating mats. They are so easy to install and great for both new build and retrofit projects. Just take the mat out of its packaging and roll out on to the sub floor. The pre-spaced cable within the heating mat means that the work has been done for you so no need to worry about measuring cable spacing.

ThermoSphere Membrane is a combined electric underfloor heating system, consisting of a decoupling membrane layer which encases an innovative electric heating cable.

The uncoupling membrane layer neutralizes the stresses caused by different rates of expansion and contraction in a tiled floor, this minimizes the risk of tile delamination and cracking, meaning once installed it stays installed.

If you are wanting to create the perfect level of warmth for a wet room, then we would recommend the ThermoSphere Membrane.

When used with compatible tanking products the wet room remains watertight for the life of the tiles with the added benefit of ThermoSphere Membrane being waterproof and coming with an IP68 rating.  It can also be used on walls for that ultimate heating experience.

Choose an Electric Underfloor Heating thermostat:

Being able to effectively control your electric underfloor heating system is paramount to getting the best out of it and reducing energy waste

When sourcing an underfloor heating thermostat make sure to look out for Lot 20 compliance. This piece of legislation came into effect in 2018 and is specifically for electrical heating products to help reduce environmental impact and help consumers achieve energy savings.

Fundamentally the more energy-saving features an underfloor heating thermostat has, the greater the compliance with the Lot 20 legislation.

For example, the Thermonet Programmable Thermostat has features which include, flexible scheduling, an automatic open window sensor an energy-saving adaptive start.

Options also include the Thermosphere Smarthome Control Thermostat that allows the control of your electric underfloor heating via a mobile app or Google Assistant and Amazon Alexa.  This functionality is great when you are out travelling, you can switch it on from wherever you are and arrive back to a warm home.

All Thermosphere heating thermostats are designed to look great and provide simple, efficient control of your electric underfloor heating – reducing energy waste and helping you create the perfect atmosphere for your home.

More importantly Thermosphere products are totally compliant and so are you when you use, specify and install Thermosphere electric underfloor heating and thermostats.

Measuring Up - Floor size, temperature and heating options:

Put simply, the higher the wattage, the faster the heat-up time.

For example, 200W/m2 is most commonly used in conservatories because they are more susceptible to heat loss. 100W/m2 electric heating mats are typically used when you require a secondary heat source or have a highly insulated property where heat loss is never going to be an issue.

Remember that you can Increase efficiency by more than 50% when you install electric underfloor heating in conjunction with Dukkaboard tile backer boards, thanks to their superb insulating qualities.

The size of the room will have a direct impact on the heat output, with larger floor areas requiring a higher heat output. It is important to bear in mind that for underfloor heating to act as a primary heat source, it will need to cover at least 80-90% of the total floor area. If the area of a room which can be heated covers less than 80% of the total floor space due to obstacles, the system is unlikely to provide enough heat, unless the home is well insulated.

The maximum power of an underfloor heating system is usually measured in Watts per square metre, with figures normally specified between 65 and 85W/m².

To guarantee the required heating output, most homes will require a heating system which provides between 150-200W/m² once installed.

Calculating your Electric Underfloor Heating requirements:

  1. The first step is to measure the total floor area, which is the length multiplied by the width of the room in m². For example, 2.5 x 2m = a total floor area of 5m².
  2. Then you need to calculate various areas in the room which will not be heated. For example, in a bathroom you need to calculate the total floor areas for the toilet, bath, sink and shower.
  3. Once calculated, add these non-heated areas together to find the total of all non-heated areas in the room.
  4. Subtract the total of the non-heated areas from the total area of the room. For example, the total non-heated area could be 1.2m², which would provide a total heated area of 3.8m².
  5. To ensure that you do not over order, reduce this figure by 10%. For example, 3.8m² reduced by 10% equals 3.42m².
  6. Finally, reduce this figure down to the nearest available heating mat size. In this example, the closest heating mat size is likely to be 3m².

If a room has multiple obstacles, many installers will prefer to use the Thermosphere Membrane, with its loose underfloor heating cables. This system makes it easier to navigate obstacles in the room. Each cable kit is designed to cover a range of floor areas as the heating output can be managed by adjusting the spacing between cables. For example, a cable spaced at 95mm instead of 75mm will provide a lower wattage but will cover a larger floor area.

The steps to calculate the exact cabling length are:

  1. As described above, calculate the maximum heated area of the room.
  2. Decide the wattage output for the room, the higher the wattage the quicker the floor will warm up. Base your calculation on the Thermospheres recommended figures of 136W/m2 or 200W/m2.
  3. Calculate how what length of cable you need to cover the floor area. Cables are then connected to a thermostat via a junction box.

Whichever system you decide to install, it is worth bearing in mind that any cables which are too long due to calculation errors cannot be cut. It is always better to use slightly smaller heating mats and cables, as any cuts to cables to make them fit will stop your heating from working.

Here at Trimline Group we stock a variety of electric underfloor heating products, including underfloor heating mats, thermostats, heating cables and heating sensor probes.

In the unlikelihood that you do experience a problem with any Thermosphere electric underfloor heating solution, don’t worry, you can relax knowing that each installation is covered by a lifetime guarantee.

To buy these Thermosphere products visit or contact a member of our experienced sales team on 020 8778 9000.


Eoin McDaid

Digital Lead

Trimline's Digital Lead since 2021, Eoin adeptly enhances online presence. Overseeing websites, social media, and digital marketing, he drives remarkable outcomes.