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Advice

Underfloor Heating

Carpets with underfloor heating

Suitability of Carpets for underfloor heating.

Most Carpets are suitable for use with underfloor heating systems at the normal operating temperature of 27˚C, it must however be appreciated that all carpets and tiles act as thermal insulation materials and this means that carpeted floor takes slightly longer to get warm initially, but stays warm longer. The choice of underlay and installation system is also critical for best performance from the heating system. Carpets and underlays resist the transfer of heat to a lesser or greater degree and this "thermal resistance value" can be measured as a "tog" value. Were manufactures have provided tog values for each of their carpets, we will show each carpets tog value on our site.

Confirmed suitability testing of carpets

Recent tests carried out jointly by the UHMA (Underfloor Heating Manufacturers Association) and the Carpet Foundation have confirmed that carpets perform better than had been expected with underfloor heating. Previous combined tog values for carpet and underlay tested under the 2 plate method have been shown to be higher than the tog value obtained when tested in an actual room set condition with carpet open to the surrounding air. The combined tog value of carpet and underlays obtained when tested under the 2-plate system can be lowered by as much as 1 tog to give a more meaningful result.

We always stress to our customers the need to give the information on tog values for their choice of underlay and carpet to the heating manufacturer to ensure that the heating system can perform correctly.

Types of underfloor heating systems

There are a variety of underfloor systems available and the manufacturers tend to recommend different maximum tog values

Water pipes buried in screed

With an underfloor system which uses water pipes buried in screed the maximum acceptable combined tog value of the carpet and underlay is often given as 2.5 tog or even higher. Most wool carpets are generally suitable for use over this type of system (We always recommend that you consult with the heating manufacturer to ensure that the carpet/underlay combined tog value is suitable for the system)

Electric heating cables buried in screed or within a suspended timber floor

These systems have a greater tendency to overheat with thicker floor coverings and for this reason a maximum tog value of 1.5 may have to be adhered to. (We always recommend that you consult with the heating manufacturer to ensure that the carpet/underlay combined tog value is suitable for the system)

Electric heating mats set on top of a structural floor

These products are generally only recommended for use under tiled or other hard floors. If however carpet/underlay is installed then suppliers of these types of matting would generally recommend that they should be covered by a flexible adhesive/levelling compound before any floor coverings are laid. This is to prevent the underlay/carpet moulding itself to the levels of the shape of cables in the matting so that they can be seen in the carpet. The maximum tog value quoted by the system manufacturer should be adhered to (We always recommend that you consult with the heating manufacturer to ensure that the carpet/underlay combined tog value is suitable for the system)

Guidelines for Installation of Carpets and Underlay

As a general rule doublestick installation systems are recommended to provide close contact between the floor, underlay and carpet allowing better heat transfer and to avoid uneven heating pockets.

Choice of underlay

There is a balance to be sought in the choice of underlay. The underlay used should allow adequate heat to pass through the floor covering into the room space above whilst also giving the carpet adequate support to enhance the carpet's performance over it lifetime.

Thermal Resistance values of Underlays

The thermal resistance of underlay is dependant on a number of factors the most important being what it is made of and its thickness. Felt, which is not normally recommended, has a greater thermal resistance than crumb rubber. Generally thinner rubber products perform best. Tog values of underlays vary considerably. Typical Tog values for felt underlays (which are not normally suitable) would be in the order of 2.5 to 2.9 togs. However in recent years new underlays have been developed with low tog values designed for underfloor heating systems such as Roma and Radiance by Ball & Young which have values of 0.8 and 1.2 Togs respectively.

Adhesives/Tackifiers

Normal tackifiers and adhesives such as F Ball F41 & F3, are suitable for use at the normal average surface operating temperature of 29˚C. However, it is important to ensure that the heating is switched off for 48 hours prior to installation and for 48 hours afterwards. In addition, after installation, the heating should be brought up to full working temperature over a period of 7 days.

Wooden Subfloor

Where the carpet is due to be laid on a wooden subfloor it is very important to ensure that adequate time has been allowed for the wood to condition whilst the underfloor heating is running to avoid variability in dimension from changes in moisture levels. We have heard of carpet fitted by the double stick method on floating wooden floors where there has been considerable problems with bubbling. Manufactures cannot be held responsible for rucking or shrinkage of carpet and underlay caused by movement in the underlying floor surface. We advise that on floating floor installations it would be better to fit by a traditional stretch and fit method so that the carpet can be easily taken up and re-stretched or re-fitted if dimensional changes occur.

This information is given as a service to our customers only. Suppliers of the flooring timbers, underlays and adhesives together with the underfloor heating manufacturer should be made aware of the combined tog values of the carpet/underlay so that the correct settings and calculations can be used.

Laminates with underfloor heating

This is a general guide to fitting laminates with underfloor heating systems you should always check with the laminate manufacture and the underfloor heating system manufacturer for their recommendation before fitting

Beforehand

The heating elements of the (warm water) underfloor heating must be embedded in the basic floor.

The tubes must be min. 3 cm underneath the surface.

The heating system must be tested according to the directions of the installer before the laminate flooring is laid.

The moisture content in the concrete floor must not exceed 1.5% (CM method).

Installation

Before you start, switch off the underfloor heating as the floor should not be higher than 18°C before, during and 24 hours after installation of the laminate.

Install the dampscreen, the underlayment and the laminate as described in the installation instructions. In case another type of underlayment is used, check its suitability to use in combination with underfloor heating.

Leave an expansion gap of 8 to 10 mm on all wall sides and around obstacles. For larger surfaces a connecting profile should be used for each ten metres and between every room so there is an expansion gap of 8 to 10 mm.

The heating

After the installation of the floor wait at least 24 hours before you switch on the underfloor heating again and increase the temperature gradually.

Always change the temperature gradually (max. 5° C/day) - also at the start and the end of the heating period the contact temperature must not exceed 28°C; the maximum warm water temperature is 50° C.

T:	04293 28128
F:	04293 29504
E:	frankscarpets@gmail.com

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