What flooring can I use with Underfloor Heating (UFH)?

Introduction

This is one of the most frequently asked questions we get. It is a very good question as this is a very important consideration.

There are a lot of variables to consider when choosing flooring to lay over UFH, such as thermal resistance, installation, style, easy to clean etc.

In short, almost any type of flooring can be used – as long as the product specification is within the suggested parameters (as set out below). 

Common flooring types

Listed below are the most commonly used flooring types, ranked from best to worst (top to bottom) for heat output.

1. Tiles/natural stone – Porcelain, ceramic, marble, travertine etc. (also includes polished concrete or similar)
2. Glue down LVT (Luxury Vinyl Tile) – Karndean, Amtico, Luvanto etc.
3. Rigid core / Click LVT
4. Laminate
5. Engineered wood
6. Solid wood
7. Carpet & underlay

The further down this list you go, the more important the thermal resistance, or tog is. Think of it in terms of tog rating of a duvet, the thicker the duvet, the warmer/more insulating it is and hence has a higher tog rating. Thermal resistance is measured in m²K/W and 1 tog = 0.1m²K/W. The UFH industry standard for thermal resistance of flooring, with any underlay is a maximum of 0.25 m²K/W or 2.5 tog combined. As mentioned in the details below, the underlay is as important as the flooring.

Important note regarding some floor coverings

All manufacturers of LVT, rigid core/click LVT, laminate, engineered wood and solid wood will state in their Ts & Cs that the floor surface temperature must be limited to around 26ºC-29ºC  (differs by manufacturer and product type). It is your responsibility to check with the manufacturer and manage the temperature. We can advise on how to control the floor temperature, to ensure you will not invalidate the floor covering’s warranty.

We strongly recommend that you inform your flooring supplier(s) and installer(s) of your intention to use UFH at the earliest opportunity.

Installation of the floor covering

The flooring should always be installed in accordance with the] the manufacturers’ instructions, paying particular attention to any instructions telling you how to climatise the flooring (if required), commissioning the UFH with the flooring applied and also what floor surface temperature the UFH can be used at. 

Flooring types in detail

Tiles/Natural Stone/Polished concrete (typically 0.00 m²K/W)

For several years now, there’s been an increasing trend in home building and renovating towards open plan living. Tiles of all kinds are generally easy to clean, but grouts can discolour over time with dirt and food and drink spillages. All the materials in this category have almost no thermal resistance at all i.e the material won’t hinder or insulate the heat at all and therefore are superb for UFH output and the warmth is felt very quickly compared to other materials.

An added advantage of tiles etc. with UFH is that they create thermal mass and hold onto heat, dissipating it long after the heating is turned off, effectively giving free heat – think of a dinner plate that’s been warmed in an oven.

Glue down LVT (typically 0.012 m²K/W)
The popularity of LVT has rocketed in recent years, whether it is for use with UFH or not, and we can clearly see why. 

A lot of people are surprised to learn that for UFH use, it is the next best product to tiles for heat output. The incredible number of designs available and realistic wood and tile effects, coupled with the easy clean nature of it has made it an extremely popular choice.

Rigid core / click LVT (typically 0.034 – 0.074 m²K/W) 

If you are unaware of this product, think of it as a cross between laminate flooring and LVT. This LVT type is not glued down and simply clicks together, making it much faster to fit (and more for the DIYer). Rigid core / click LVT often has a thin underlay as part of its construction which also improves soundproofing. It usually has a lower thermal resistance than laminate flooring.

Laminate 8mm – 12mm (typically 0.06 – 0.09 m²K/W) 

The main component of laminate flooring is HDF, High Density Fibreboard. All types of wood and fibreboard-based flooring will hinder heat slightly as they are insulating materials. The thermal resistance of laminate is less than other types of wood, it has a better wear layer and more resistant to damage, so therefore a good choice over engineered or solid wood etc. We recommend that an underlay with perforations and/or specifically for UFH is used and your supplier will be able to advise you on this.

Engineered Wood 14mm – 18mm (typically 0.1 – 0.12 m²K/W) 

Similarly to LVT, engineered wood has really increased in popularity over the last 10 years. The herringbone look is by far the most common style we see. Engineered wood flooring is made from around 6-9mm of plywood layers with a 3-6mm layer of solid wood on top. The plywood layers make this composition very strong. You get the solid wood look in a stronger format, making the flooring more stable than solid wood – this is particularly important when using it with UFH.  We always recommend engineered wood flooring over solid wood flooring.

Solid Wood 14mm – 22mm maximum (typically 0.12 – 0.18 m²K/W) 

Solid wood can be used with UFH, but it needs very careful consideration. Some suppliers and manufacturers of this product will not warrant it over UFH. Because of the completely natural make up, rather than being strengthened like engineered flooring, it can move more than normal with the UFH.

Carpet & underlay (typically 0.15 – 0.25 m²K/W) 

Most people want carpet in their bedrooms and why not have UFH in there too? Yes, carpet can be used with UFH! Remember though that carpet is an insulator. 

As above, the maximum tog rating is 2.5 and we would always say to keep the tog rating to the absolute minimum – pick the thinnest carpet and underlay you’re happy with, so as not to hinder UFH performance. That said, with carpet being the warmest material in this list, it is warm underfoot, even without UFH warmth. We have found over the years that rooms with carpet tend to have the UFH set at 1ºC-2ºC less than rooms with other types of flooring, which improves efficiency. We recommend underlays that are specific for UFH use and your supplier will be able to advise you on this. 

Examples of heat output by floor covering

Please note that this is a guide only. Thermal resistance varies by manufacturer products within the flooring types. The following outputs are based on a 50ºC flow temperature, 20ºC room temperature, and an in-screed UFH system with pipe at 200mm spacing on insulation.

If you would like to discuss this article, have some questions of your own or would like to discuss
your project then please don’t hesitate to get in touch.

VarioHeat Ltd
Unit 5 Tanshelf Industrial Estate
Colonel’s Walk
Pontefract
WF8 4PJ
01977 798720
damien@varioheat.co.uk