How to Install Underfloor Heating


Underfloor heating has often been seen as a luxury, however it is fast becoming a popular and increasingly affordable solution to heating homes. To make sure your underfloor heating is as energy and cost efficient as possible, it is important to make sure it is installed properly.

We have put together a quick and easy guide for installing your underfloor heating, including a list of everything you’ll need before you start.

Before you begin

Before installation make sure your underfloor heating system is suitable for the type of floor and room you are intending it to be used for. Many systems are not suitable for use within wet environments such as bathrooms and wet rooms, whilst some systems are specifically designed for use with certain types of flooring such as tile, laminate, wood or marble. Consider also where within your house the underfloor heating will be placed, as higher wattage systems are available for areas with greater heat loss, such as conservatories.

What you will need

  • Dustpan and brush,
  • Floor primer
  • Insulation boards
  • Heating cable/heating mat
  • Adhesive tape
  • Thermostat

Here at Building Supplies Online we offer Flexel underfloor heating kits to help you make sure you have everything you need.

Preparing the subfloor

For the best results, you will need to prepare the surface your heating system will be laid on. Whilst it may be an additional cost at the time of installation, laying insulation boards on the subfloor will help to reduce heating costs in the long run by preventing downwards heat loss. Whether using insulation or not, use your dustpan and brush to ensure the subfloor is clean and free of dust, before applying your floor primer evenly over the surface; this will help to make sure the adhesive tape used to secure the heating systems will stick.

After allowing the primer to dry, use a pen to mark out the area that will be covered by the heating system and where the wires will be placed, leaving a border of at least 50mm at the edge of the room. Make sure you leave space for any permanent fixtures such as sinks, baths or counters – underfloor heating should not be installed directly underneath these. Finally, cut a groove within the subfloor near where the thermostat will be placed for the installation of the thermostat probe.

Installing underfloor heating cables

Before laying your cable, you should test its resistance using an ohm metre to make sure that everything is working properly. This is a problem that is much easier to fix before installation than after. Having done this, begin to roll out your cable until you reach the meeting point of the cold tail and the orange heating cable – this is the part you will be laying on the floor. Beginning close to wear you will install your thermostat, lay your cable in a line along the previously marked out area. Try not to unravel too much of the cable at one time. Once you reach the border you created, loop the cable back and lay another line parallel to the first.

These lines should have a gap of at least 50mm between them. As you lay out these loops, fasten each one with small pieces of adhesive tape. This will secure them whilst you continue working, but will allow you to adjust the cables afterwards if need be. Once you are happy with the layout of your cables, making sure they are sufficiently spaced out and you have no cables crossing, secure the entire length of your cables with adhesive tape.

Installing underfloor heating mats

Just as with the cables, before laying down your heating mat make sure you check the resistance. Once happy with this, begin to roll out your heating mat within the marked-out area, beginning at the location of the thermostat. Having rolled out one length of the mat, cut the mat itself, making sure you do not cut the orange heating cable. Then, turn the mat and run it back the other way, lying parallel to the one before.

When turning the mat, make sure the cables do not become twisted, and that they are still at least 50mm apart from each other. Having covered the necessary area, adjusting any mats where necessary, you can now use the self-adhesive strips to fix your mats to the subfloor. For added security you may choose to use additional adhesive tape or hot glue on the edges of the mats to make sure they are firmly in place.

Once you have laid out your heating cable or mat, a qualified electrician should be used to connect the cold tail cable to the power supply, as well as installing the thermostat. You should then use a self-levelling compound or appropriate adhesive before laying down your choice of flooring.