30 Mar 2017

How different floor types respond to underfloor heating

The self-build market is increasingly turning to underfloor heating (UFH) over alternative radiator solutions. However, the practicalities of incorporating UFH systems into a self-build design project depend on several considerations. In this feature, Nigel Sanger, Technical Manager at JG Speedfit, a leading underfloor heating specialist, looks at how different floor types respond to UFH.

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Underfloor heating, both wet and dry, is compatible for installation with the wide majority of floor systems if there is enough space available to build-up the floor. However, the type of flooring does affect the overall performance of a system. While it is widely accepted in the self-build and installer networks that flooring material which offers good conductivity is the most effective for UFH system performance, not every project is the same.

As such, there are several variables to consider. For any self-build project, be it a new-build or a retrofit, it is important to understand the suitability of different floor surfaces and how this affects heat up times, heat outputs, energy efficiency and overall system effectiveness. Surfaces with a low thermal resistance, ceramic and stone are often the preferred floor types for underfloor heating installation, and are consistently used in self-build projects. Heat transfers quickly and easily on these surfaces, making them ideally suited to rooms with high heat loss, such as conservatories.

Screed solutions

If you are planning to have underfloor heating installed on these surfaces during a self-build project, you do need to bear in mind that you will require a screed solution, which means the pipes will have to be buried in a screed on top of the floor insulation. Be aware that a screed construction will expand and contract with the heat. In the screed, this is absorbed by an expansion gap and edge insulation, so ensure that any tiles on the surface are also laid with an expansion gap around the perimeter of the room. For improved aesthetics, this gap can easily be covered with a skirting board, for example.

There is a common misconception that timber wood floors are all highly compatible with underfloor heating systems. However, not all wood is the same. Typically, self-build projects will utilise solid, laminated and engineered timber flooring, which all have different densities and mechanical strength.

It is important to consider moisture when using a wooden surface. As a natural material, wood absorbs humidity, and this can dry the timber out, causing shrinkage in the panels, or forming gaps between the floorboards. This makes it important to assess the moisture level of the floor prior to installation to calculate the right heating cycle for underfloor heating systems. The heat should be restricted to 27ºC using floor probes and the supplier should always be consulted for best practice recommendations when installing underfloor heating. Suspended timber floors also tend to move a lot more than screed but this can be controlled by using tiles to cover the joists, and tying them down securely with flexible adhesive and grout.

Despite many popular misconceptions, carpet can be laid over a wooden surface when underfloor heating is installed; you just need to ensure you have the correct combination of carpet and underlay. Quality manufacturers will have technical information available to help make sure you get this right.

Vinyl and linoleum are very popular flooring surfaces in the self-build market, because they enable a high-quality finish that allows for more customised interiors, without breaking the bank. However, due to the poor thickness of these surfaces, it can be more difficult to make underfloor heating compatible with vinyl and linoleum. The homeowner needs to ensure the system is installed with a suitable sub-floor. Solid screed, concrete or joisted wood are often the best choices, over-floor panels should also be used for additional insulation. The heat should be restricted to 27ºC post-installation or whatever the manufacturer’s recommendations are, by using floor probes to prevent damage to the material.

A more traditional and aesthetically-comfortable floor surface for self-build projects is carpet, and this can be compatible with underfloor heating, but special attention should be given to the underlay. Underlay acts as an insulator when the system is turned on, extending warm-up times and delaying the passage of heat.

Although felt is one of the most commonly used materials for underlay, this should be avoided because it is most likely to block heat. Instead, a low-resistance underlay material should be used, ideally with a woven fabric-backed carpet. This will ensure that high levels of heat efficiency are realised.

JG Speedfit offers underfloor heating systems that are suitable for almost any floor finish, delivering exceptional results for a range of surfaces including ceramic tiles, carpet, vinyl and wooden floors. With leak-proof, push-fit connections, its plastic fittings and pipes are manufactured in the UK using cutting-edge technology, designed for quick and easy installation in commercial and domestic properties.

Of course, an underfloor heating system is only as effective if it is installed to be fully compatible with the floor surface. The floor always plays an instrumental part in the overall heating system, with the thermal resistance and insulation ability affecting the output from the floor. Self-builders are advised to consider the choice of floor surface very carefully in any project, and should be aware that the higher the floor thermal resistance, the lower the heating effect and therefore the longer the warm-up time. Typically, coverings that have low thermal resistance are the most suitable for underfloor heating installation when additional factors have been considered.

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