Underfloor heating is gradually becoming almost the norm these days, not only as a heating system but also as a comfort feature in the home. Almost everyone has heard of the pleasant sensation provided by warm tiles in the bathroom, and most of us know at least one person who uses this form of comfortable heating. That is why hardly anyone asks whether it is possible to install heating mats in the adhesive beneath the tiles – it is taken for granted and no one gives such an application a second thought. However, the situation is somewhat different for other types of floor covering.
Customers often turn to FENIX Group, as a manufacturer, to ask whether it is possible and advisable to lay something other than just tiles over electric underfloor heating. Of course, it is possible, and almost all manufacturers of the various types of floor coverings also offer a variant suitable for use with underfloor heating. For new installations, this is usually no problem at all – for tiles, PVC and carpets can easily be fitted with ECOFLOOR heating cables or heating mats in flexible sealant or self-levelling screed; for floating floors, the FENIX Group offers ECOFILM electric heating foils. However, the situation is more complicated for retrofit installations or renovations. As mentioned above, the comfort of a warm floor is nothing out of the ordinary these days, and if a homeowner is already renovating their flat or house, why not treat themselves to it?
Sometimes, however, it is not straightforward. We are often approached by customers seeking our advice. They are interested in underfloor heating for a living area, with carpet or PVC as the top layer. They don’t want ceramic tiles, and they aren’t considering laminate flooring. Wet methods – i.e. various floor screeds and sealants – are out of the question for a variety of reasons. In most cases, their interest then turns directly to ECOFILM heating foils, which they consider ideal – it is a dry process, the foil is very thin and heats the entire surface. However, even ECOFILM heating film cannot normally be laid directly under carpet or PVC. After all, it is a heating element operating at 230V mains voltage, and these floor coverings do not provide sufficient protection; and there is also a real risk of the carpet or PVC bunching up or buckling if you move heavier objects – such as an armchair or a sofa – across it.
That is why the FENIX Group offers the HEAT-PAK floor panel. This is a special underlay made from compressed cellulose, which the FENIX Group imports from the Netherlands. The panels have a high bulk density (770 kg/m³), making them very hard, with a flexural strength of >40 kg/cm² and good thermal conductivity (thermal resistance R=0.047 m² * K / W). When combined with ECOFILM heating foils, these panels form a dry-installation system specifically designed for renovations and the retrofitting of underfloor heating beneath carpets or PVC flooring.
Recommended installation method
Thanks to their good thermal conductivity, HEAT-PAK panels can be placed between the ECOFILM heating foil and the carpet/PVC without adversely affecting heat transfer into the room. The panels themselves are sold in packs in two thicknesses – 3 and 4 mm – which are laid on top of one another. The panels are factory-coated with an adhesive layer, so that when stacked, they form a rigid 7 mm-thick structure which provides the heating film with the necessary protection against damage, whilst being hard and sturdy enough to allow carpets and PVC to be laid directly on top.
- Wear layer – carpet or PVC
- HEAT-PAK 7 mm – a two-layer structure bonded with staggered joints (3 mm base layer, 4 mm top layer)
- Vapour barrier – PE film, min. thickness 0.20 mm
- ECOFILM heating foil 40 W/m² (60 W/m², 80 W/m²)
- Floor insulation made of extruded polystyrene (min. 3 mm)
- Existing floor
The installation method is as follows:
We lay thermal insulation on the existing floor, which also protects the heating film from any unevenness in the subfloor. We lay the ECOFILM heating foil, with a maximum power of 80 W/m², on top of the insulation. We cut grooves in the insulation for the supply cables and lay a PE foil with a minimum thickness of 0.20 mm over the heating foil. The PE film serves as additional electrical insulation and also protects the heating film from any moisture. We now lay the HEAT-PAK panels in two layers. First, the bottom row of 3 mm panels, onto which we then glue the top row of 4 mm panels. The top row must be offset so that it overlaps the joints of the bottom row, and vice versa – this prevents the joints from showing through the carpet or PVC, whilst ensuring the entire surface forms a single, continuous unit. The thermostat probe, which will regulate the floor temperature, is placed in a groove cut into the HEAT-PAK panels beneath the heating foil.
Laying all the layers is very straightforward, and if you use the ECOFILM Set, you won’t need any special tools at all apart from a sharp knife and a rubber mallet. You can use the knife to cut the floor insulation, the PE film and the HEAT-PAK panels. By tapping the top row of HEAT-PAK panels with a rubber mallet during installation, we ensure perfect adhesion and bonding between the two layers. The thickness of the entire structure (floor insulation, ECOFILM, PE film, HEAT-PAK) is just 10 mm! Carpet or PVC, as the top layer, can then be glued to the panels as standard, or simply laid loosely.
Heat-up testing
As FENIX is committed to the quality of the products it offers its customers, it always tests them thoroughly before they go on sale. Similarly, the HEAT-PAK panels were tested in a test chamber to determine how and at what rate temperatures spread through the structure when combined with the ECOFILM heating foil. The tests were designed to confirm the good thermal conductivity of HEAT-PAK panels and to rule out the possibility of the heating film overheating. The ECOFILM heating foil itself has a temperature resistance of 90°C, which cannot under any circumstances be reached at a power input of 80 W/m². However, if the HEAT-PAK panels did not possess the declared thermal conductivity, undesirable heat loss into the substrate would occur, leading to a significant deterioration in the system’s economic and operational performance. First, load tests were carried out, during which the entire structure with the heating film was operated without any regulation. The aim was to determine the rise-up dynamics and the maximum temperatures that can be achieved.
The entire test took place at a room temperature of approximately 24°C, which was maintained by air conditioning. The graph shows an initial, relatively rapid rise in temperature; subsequently, the carpet’s higher thermal resistance became apparent and the temperature difference between the individual layers began to increase. After nine hours of operation, the temperatures stabilised – at 32.7°C for the carpet and at 36.2°C on the surface of the heating foil within the assembly. The graph also demonstrates the good thermal conductivity of the HEAT-PAK underlays – even at maximum temperatures, the difference between the temperature of the heating foil’s surface and that of the HEAT-PAK underlay was just 1.6°C.
In a further test, a thermostat probe was placed in the underfloor heating system, maintaining the temperature at 27°C. For the first three hours, the floor with HEAT-PAK panels was operated without a final wear layer; afterwards, a carpet was laid on the floor – in the graph, the temperature on the surface of the carpet is shown by the green curve.
Carpet was chosen deliberately because it has a higher thermal resistance than PVC and can therefore be described as a ‘worse’ option in terms of heat transfer. The graph shows that, for the floor not covered by carpet, the temperature difference between the heating foil and the surface of the HEAT-PAK panel is less than 1°C. The response time is also very good; the floor warmed from 24°C to 27°C in just under 20 minutes, which is the same as in the first test. This once again confirms the good thermal conductivity of the HEAT-PAK panels.
The probe of the thermostat, which was set to 27°C, was placed on the surface of the HEAT-PAK panels. The graph shows a certain degree of thermal inertia in the HEAT-PAK panels, which is due to the greater volume of material. Consequently, the temperature of the panels was more stable during the heating foil cycling. When covered with a carpet, their surface temperature increased by an average of approximately 0.5°C; the temperature difference between the foil and the HEAT-PAK panel remained within 1°C, and the temperature on the surface of the carpet was only 0.5°C lower than on the surface of the HEAT-PAK panels.
The tests carried out demonstrated the suitability of this design for underfloor heating applications beneath carpets and PVC. FENIX is therefore able to offer a technical solution to customers who are considering underfloor heating beneath carpets and PVC flooring, but who are unable or unwilling to lay a new concrete floor.
