Electric Underfloor Heating and the BSI 17th Edition IEE Wiring Regulations

The BSI 17th Edition IEE Wiring Regulations, which come into force for all installations designed after 30th June 2008, introduce specific requirements for all installations of electric floor heating systems used within buildings.

The following commentary reflects Heat Mat's interpretation of these guidelines and how they will affect the planning, design and installation of future electrical underfloor heating projects. The vast majority of the requirements have been considered as either 'best practice' or as a specific requirement by the majority of quality underfloor heating suppliers in the UK for some time. It is now specified that all systems must be protected by an RCD with a rated residual current not exceeding 30 mA, a recommendation that most suppliers have been making for many years. The regulations also state that any products that are installed into a floor of concrete or a similar material must have a degree of ingress protection of no less than IPX7, and our interpretation is that this includes systems laid beneath tile adhesive.

Yet again, the vast majority of quality products meet these specifications. Section 753.411.3.2 states that for any heating units that are delivered from the manufacturer without exposed-conductive-parts, the installer must place a suitable exposed-conductive-part, such as an earth grid, above the underfloor heating system. We believe that this requires all mains voltage underfloor heating systems to be suitably earth protected for safety. If our interpretation is correct, then all of the un-earthed systems currently sold for use directly beneath laminate floors and tiles, including carbon films, will now require some form of earthing grid to be installed above them in order to comply with the 17th Edition, significantly adding to the installation time and cost.

Section 753 also introduces a requirement that the floor temperature itself is limited to 80°C, and that the system can also limit the floor surface temperature in areas where people will walk. The simplest way to satisfy these requirements is to install a thermostat with a floor temperature sensor and program the thermostat appropriately. In addition to all of the above requirements, the installer of an underfloor heating system is now required to ensure that complete details of the system are left for the owner of the building along with full usage instructions, and these must be permanently fixed near the relevant distribution board.

The simplest way to comply with these requirements is to ensure that you install systems that have instruction manuals designed to help you meet these demands, by including as much of the required information as possible within them. For the electrician, it appears that the best advice continues to be to install products that carry independent British system approvals, such as BEAB, and to only install products supplied by manufacturers who understand the legislation and can assist the installer in meeting their requirements. The above commentary reflects Heat Mat's interpretation of the 17th Edition rules in relation to electric underfloor heating systems, and should not be used as a substitute for individual interpretation of the legislation. For further information on the 17th Edition, and how Heat Mat can help you fulfil your responsibilities, please contact us on 01444 247020.