An Introduction to Heating Cable Technology
Introduction
Heating cables used in underfloor heating applications, are a far cry from those originally used in the 1960s. In those days, the only option was to embed heating cables into thick, poorly insulated, concrete floors, making underfloor heating systems uncontrollable, uneconomical and because of the quality of the available technology, largely unreliable. Electric heating cables today, feature fixed resistance or self-regulating elements spiralled into single or twin, core cables, complete with moulded insulation. They are typically produced on spools or reels so that cabling can easily be cut to length and laid as required, or, embedded into foil or polyester to form a heating film or mat that can be installed quickly and easily.
A room with a small floor area, possibly with nooks and crannies such as a bathroom for example, may be perfectly suited to the installation of single heating cable, but larger, perhaps more regular rooms may benefit from heating mats which do not need to be spaced or taped in place before laying the floor covering.On the whole, Electric heating cables are easier to install and require less space than "wet" underfloor heating systems and provide uniform heat output along the entire run of cable.
Heating Cable Characteristics, Benefits & Considerations
There are basically three different types of heating cables used in underfloor heating and more than one of these may be used in a single installation. So-called "standard" heating cables are used in dry areas, but there are also shielded or screened cables and those of the "extra thin" variety which are again screened but lack any outer insulation.
Advances in cable technology now mean that it is possible to produce "loose lay" heating cables with diameters as small as 3mm, which when combined with the height of tile adhesive or grout required only raise the height of a floor by a maximum of 10mm. Heating cables are typically insulated with silicone rubber making them suitable for applications over a wide range of temperatures, in fact from 60°C below freezing to 250°C above, and supplied with cold leads of sufficient length to allow them simply to be laid in evenly spaced loops and connected to a thermostat.
Generally speaking, a heat output of at least 80w/m2 is required in newly built homes or those where original insulation has been supplemented and 80w/m2, or more in older properties. In fact, heating cables are typically available with outputs between 100w/m2 and 200w/m2 depending on the climate and whether or not underfloor heating is to be employed as the primary heating source or as a comfort measure.
Electric heating cables should be looped across the shorter width of a room in a pattern resembling a snake. This does by necessity involve more 180° bends than looping along the length of a room, but also means that less cable becomes redundant if the cable needs to be cut, by way of repair.
The floor under which heating cables are to be laid should be measured accurately, taking note of any permanent fixtures, such as kitchen units, showers or baths. Such solid fixtures may produce "hotspots" and potentially damage to floor coverings because the radiation of heat from the floor is impeded. As far as less permanent fixtures, such as furniture, are concerned self-regulating heating cables can sense heat from other sources such as the Sun itself, or electrical appliances and adjust their own heat output accordingly, so you can position your furniture to take maximum advantage of all these heat sources. Self-regulating cables are suitable for installation onto subfloors and beneath floor coverings, of many different types, including timber, engineered wood, or laminated floors, in wet and dry areas.
Generally speaking, if electric heating cables are to be laid on a timber subfloor, existing floorboards must be sound and level and possibly strengthened with moisture resistant chipboard, or plywood. Un-insulated subfloors should similarly be laid with extruded polystyrene insulation board, of which many well-known brands exist, some of which feature a fibreglass mesh embedded in cement polymer to an appropriate depth, so that heat travels up into the floor covering and the room above, rather than down into the subfloor. The depth of insulation may be restricted by the level of the floor and the height to which it can be raised, but 10mm is more than adequate in most cases. If the floor is to be tiled, tile adhesive or a flexible, self-levelling compound, and then tile adhesive, should be spread evenly on the floor, in the same direction as the cable runs, covering the heating cables completely. It is advisable to use a plastic trowel, rather than a sharp, metal trowel for this purpose, to prevent damage to the heating cables.
Further heating cables Information
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