It has been mooted that underfloor heating (UFH) will become the heating method of choice over the next few years. There are various reasons for this, including the rising of energy costs and incoming regulations from government on heating alternatives compatible with renewable energy sources, as well as overall changes in consumer outlook and interior design trends.

This means that the UFH market is likely to boom in the next few years, and installers will benefit from being well versed in fitting various types of UFH to suit different customer needs. 

Underfloor heating can be used with a variety of floor finishes – from carpet to vinyl and laminate, through to the thermally ideal finish, ceramic tiling. Its low tog value – typically 0.1 – allows for a more efficient heat transfer.

However, ceramic tiles can also be prone to cracking if the UFH is not installed correctly, or if certain conditions are not met during fitting, screeding, pressure testing, and commissioning.

Certain crucial steps should be taken to ensure that the tiles do not crack and that the UFH pipework is laid correctly.

Step 1 – Plan your project

The first step of any UFH installation is to plan the project out, understand the floor construction and, importantly, the space that you are working with. 

Typically, newbuild homes will have a solid concrete floor. This is followed by insulation, which the underfloor heating pipework will be fixed on top of, before being screeded over. Finally, the floor finish goes on top of the screed.

There are several considerations and factors to bear in mind but, crucially at this stage, installers must remember that the insulation depth should comply with Building Regulations. This is to ensure that any downward heat loss does not exceed 10 watts per m2, in accordance with BS EN 1264.

Step 2 – Plan your pipework

After understanding the floor structure, you’ll need to look at the space you are working with. This will determine the pattern in which you lay the UFH pipework – whether it’s in a serpentine or counterflow configuration.

Serpentine is a simple up and down circuit pattern that is especially good for irregular shaped rooms, such as kitchens with an island or rooms with a bay window. Meanwhile, counterflow installation works well with square rooms. You can even combine both pipe layouts if required.

Planning how the pipework is laid out should be done during the design stage. As part of RWC’s JG Underfloor service, CAD drawings can be made available as long as the necessary level of detail is provided, which can then help when it comes to the installation.

Regardless of which pattern you choose, always remember to plan your route to and from the manifold, and out of the room, to avoid mishaps.

Step 3 – Choose your UFH fixing system

Once the pipework has been planned out, the next stage is to move to the installation and laying of the pipework.

Before laying the pipework, the insulation must be flat, and edge insulation should be installed throughout the room – this is to account for the expansion of the screed as it cures, to prevent it from cracking when it pushes against the edge.

Then, it’s down to choosing the system to fix the pipework, from the three main systems available for concrete floors.

First is the UFH staple system. With this system, the pipe is stapled down to the insulation using a staple gun. This system is the most cost effective of the three solutions, but the pipework needs to be marked and spaced out properly first – typically 200mm should be left between each circuit – which can add time to the project.
Next is the mounting rail system. The mounting rail is taped to the insulation with the supplied pins, and then the pipework is slotted into nodules on the rails. The key benefit is that installers can count between each nodule on the mounting rail to easily space out the pipe circuits.

Finally, there’s the floor panel system, which creates a simple grid to ensure quick and easy laying, and provides a precise guide for the pipe. As each ‘egg box’ gap where the pipe sits in the floor panel is 50mm, this makes pipe laying quick and simple – arguably making it the fastest system to work with.

Step 4 – Pressure test, screedibf, and tiling

After the pipework installation, a pressure test should always be undertaken, using water. 

A common misconception is that testing with air is enough. However, doing so will not allow the pipes to expand fully, simply because air, unlike water, can be compressed. It is also important to make sure there aren’t any traces of air in the system, which can have a detrimental effect on how the system runs.

Best practice is to perform the following pressure test before any flooring or screed is laid. Firstly, raise the pressure to 2bar for 10 minutes. Then, after 10 minutes, increase the pressure to 10bar for a further 10 minutes. Finally, reduce the pressure back to 6bar and leave it pressurised.

This will allow for any leaks to be detected and ensure the pipes reach maximum expansion. Maintaining the pressure until it has been fully laid and cured will also prevent it from cracking later on. 

Step 5 – Slowly bring the water temperature up

Once the screed has cured and the ceramic tiles have been laid, installers should slowly build the temperature up in the pipework. 

This is because the screed and the tiling adhesive can weaken if the heat builds up too fast after installation, potentially leading to cracking of the adhesive, as well as tile movement. 

On screeded floors, the initial water flow temperature should be maintained at 25ºC for three days. On day four, the temperature can be increased gradually, in increments of 5ºC a day, until the maximum design temperature is reached. Finally, it also must be maintained for a further four days at maximum design flow temperature.