Carpet & Underfloor Heating

In recent times underfloor heating has become increasingly popular for new-build residential and commercial developments. Modern underfloor heating systems are considered an extremely efficient and comfortable option for heating the home. In order to maximise the effectiveness of any underfloor heating system installed it is important however to get the right combination of floor covering to complement the system being considered.

Traditionally heavy Axminster and Wilton carpets have been installed in the home for their comfort factor and their heat insulation properties. Up until recently under floor heating companies have recommended that the combination of underlay and carpet should have a heat resistance of no more than 2.5 ‘togs’ for their systems to work efficiently. Some of our heavier wool rich carpets have tog ratings of between 1.5 – 2.0. If these are combined with underlay with a ‘tog’ rating in excess of 1.0 it has been argued the performance of the heating system might be compromised. Research carried out by the Under Floor Heating Association (UHMA) in conjunction with the Carpet Foundation has found that carpets and underlay actually perform very well with underfloor heating systems up to a combined ‘tog’ rating of 3.5. Rooms with the heavier combinations do take slightly longer to heat up but actually hold their temperature for longer periods. As a rule of thumb it is now recommended that a figure of 1.0 should be subtracted from the combined ‘tog’ value of underlay and carpet when assessing suitability for underfloor systems. It is important however that specialist advice is sought when choosing the best combination of floor covering to suit the particular heating system being installed.

Types of underfloor heating systems

There are several different systems available for under floor heating. These include:

- Water pipes buried in a concrete screed
- Electric cables buried in screed
- Electric Heating mats set on top of a structured floor

Each system has stringent technical specifications as regards installation that need to be followed to ensure a successful outcome. The manufacturers of these systems will advise the type of floor covering most suitable for use with their particular system. It is very important that these recommendations are followed, as mistakes can be costly to correct after installation is complete. E.g. If underfloor heating is to be installed over a wooden sub floor it is important to ensure the timbers are completely dried out before installation. Heat from the system can cause movement of unseasoned timber that can show through the installed carpet and can cause unsightly wear marks in time. Also if using an electric mat system some form of flexible levelling compound should be used to fill all gaps to ensure an even surface for the installation of the underlay and carpet. As with any carpet installation the floor should be level, as otherwise imperfections are likely to be felt underfoot when the project is finished.

Choice of underlay

Several underlay manufacturers now supply specially formulated products for laying over underfloor heating systems. These have a flat profile and have tog ratings of 0.8 or less that allow heat to rise virtually unimpeded. Dispensing with underlay or using a light or overly thin underlay is not recommended, as this will compromise the comfort feel of the installed carpet.

Use of adhesives

If it is required that the carpet or underlay has to be stuck to the floor it is important that this is done carefully. Normal tackifiers and adhesives can be used at the normal operating temperatures for underfloor heating systems. It is very important to ensure that the heating system is switched off 48 hours prior to installation and for 48hrs afterwards. The system should then be gradually brought up to full working temperature over a 7 day period.

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