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Installing Wet Underfloor Heating

If you are considering a wet underfloor heating system for your property, this guide will give you an idea of what’s involved with the installation.

If you are at the design stage of a new build, then now is the right time to look into the types of heating systems available.

If you have already chosen to use water based underfloor heating, it is important to integrate the system into the design, to reduce fitting costs and time on site when it comes to installation.

How the system is installed

It is important to research the types of wet systems available.

Wet underfloor heating being installed.

A series of pipes are laid under the floor, and warm water is circulated through them to heat the floor, and is then returned to the boiler or heat source.

The loops of pipe work are usually laid into the floor screed during construction, which is why this method of heating lends itself to new buildings rather than refurbishments.

Insulation is laid underneath the heating system to prevent heat loss through the ground, and to reflect the heat upwards towards the floor.

The piping is connected to the boiler via one or several manifolds which control the flow of water to each zone within the system. With most systems, each room has its own thermostat, which is linked to a timer and control unit; much like conventional central heating.

In a typical installation there will be approximately five metres of pipe per square metre, laid at 200mm centres.


How long does it take?

Installing a wet system into a typical new build house could take between 2-4 days, but larger or more complicated installations will invariably take longer. If the heating is to be installed in an existing property, there will be a reasonable amount of preparation work to do before the pipe can be laid.

Getting as much of the floor prepared as possible in advance can reduce the time tradesmen need to spend on site, and therefore reduce the cost of the fitting.

The existing flooring can be taken up, and any dust and debris swept away. The closer you can get down to the subfloor the better; but if it requires digging work, its best left to the experts.


Tips on preparation

For wet underfloor heating systems, preparation begins at the design stage. The type of system and the layout of the pipes must be pre-determined by the heating requirements.

Water based systems can heat the floor to a maximum of 100 watts per square metre, so it is essential to assess the systems ability to fully heat the property.

The type of flooring must also be considered as some have limits on thermal tolerance, and the kind of finish you use will affect the performance of the heating system.

The manifold valve assembly needs to be fitted somewhere in the system. Usually they are tucked away in a cupboard so they are out of sight, but accessible for servicing. Plan the system and pipe runs so that the manifold can be placed in a convenient position.

To prepare for the installation, clear the floor of any dust and debris, and ensure that the surface is perfectly flat and even. The floor insulation and edge insulation, can be laid in advance to save the fitter time on site.

Edge insulation has two purposes, it prevents any lateral heat loss into the walls and also acts as an expansion gap for the floor and the screed as they expand and contract with the heat.


Things to look out for

One of the more common mistakes is to fit a type of flooring, which does not work effectively with the particular heating system that has been used. A little bit of research into the best kinds of flooring is worth doing, as the right flooring will aid better performance and greater efficiency.

Ensure that your chosen flooring will be right for your system

Research to find the best flooring for wet underfloor heating

Cork and softwood floors are not usually suitable for use with an underfloor heating system, and some laminate boards have an underlay which is too thick (more than 2mm) and insulates against the heating.

Natural stone or concrete, and slate or ceramic tiled floors all provide excellent heat transfer and compliment underfloor heating.

If Lino or Vinyl is used it should not be thicker than 5mm, while most carpets are fine as long as they do not exceed 12mm in thickness.

The system should be filled and tested to a pressure of 6 bar before the screed is laid; make sure your installers do this, as any leaks or weak points are better identified at installation rather than at some point in the future, when damage has been caused.

Doors and windows should be in place and interior walls finished before the installation; this helps to ensure the correct location of the pipe work.


Can you do it yourself?

The laying of a wet underfloor system is probably best left to experienced plumbers and electricians. The work has to be signed off by a competent and qualified person, so unless you happen to be a tradesman, you will need the experts for this if nothing else.

An experienced DIY enthusiast may be capable of installing a heating system, and you might want to take the challenge on yourself.

If you are set on carrying out your own install, make sure you are fully conversant with the plans; also be well prepared and have all the tools and equipment ready and on site.

You will also need to look into local regulations regarding the signing off of the work you have completed.



Water based systems are the most energy efficient type of underfloor heating, as they use heat from a gas boiler rather than using the mains electricity to heat the floor.

They are versatile systems which can be linked to renewable sources such as solar panels, potentially making them even more energy efficient.

The installation process is complicated, but a system can be fitted quickly and easily by experienced fitters on a new build, as the heating is part of the design and part of the construction process.

Installing a wet system into an existing property can cause a variety of headaches, from the digging up of the floor, to the raising of the floor level to accommodate pipe work; in general, the cost of installing this system in a refurbishment is prohibitive.

If the system is integrated into the design, and fitted with a floor finish that allows maximum performance, wet underfloor heating can be energy efficient, while providing a touch of luxury at the same time.


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