Cable and foil underfloor heating under tiles in the bathroom

Recommendation points

• Classic underfloor heating system
• Selection of heating elements
• Placement of the thermostat
• Connection diagram
• Floor heating installation

Tiled floors feel cold due to their high heat capacity. To combine aesthetic qualities with comfort, you can use electric underfloor heating using cable or foil systems. Our instructions for arranging a warm floor in bathrooms will explain the key points of calculating and using a warm floor in a bathroom..

Classic underfloor heating system

The story about the intricacies of installing an electric underfloor heating under a tile should start, perhaps, with a description of its device. This heating system is based on the combined effect of three components: thermal insulation, heating elements and a protective absorbent screed. Let’s consider each component separately.

Thermal insulation is needed not only for more economical energy consumption. Floor heating in the bathroom, as a rule, is not always on, therefore the speed of reaching the operating mode is very important. With the correct use of the thermal insulator, it is possible to achieve the surface temperature reaches the specified values ​​in just 3-5 minutes.

Laying of cable underfloor heating under the tiles: 1 – overlap; 2 – rigid thermal insulation; 3 – heating cable; 4 – cement-sand screed; 5 – tile adhesive; 6 – tiles

The function of the heating elements is obvious, but additional requirements are imposed on them. In particular, the use of underfloor heating in rooms with high humidity requires compliance with electrical safety standards. It is also necessary to correctly calculate the power applied to a unit of area, otherwise the floor will be either too cold or unbearably hot..

The underfloor heating screed is often overlooked, although it is the most important functional element. And although the process of filling it is a topic for another conversation, understanding the basic principles of the device will help determine the type of heating elements and the method of their installation. In the underfloor heating system, the screed solves three tasks at once:

1. Fixation and protection of heating elements from mechanical damage.
2. Forming a flat and hard surface for laying flooring.
3. Even heat distribution and increased thermal inertia.

Installation of infrared warm floor under the tiles: 1 – rough floor; 2 – rigid thermal insulation; 3 – heat-reflecting material; 4 – infrared film; 5 – polyethylene film; 6 – mounting grid; 7 – cement-sand screed; 8 – tile adhesive; 9 – tiles

In order to fulfill all its functions, the screed must be of adequate thickness and have sufficient strength. We will give some recommendations regarding these qualities as the story progresses..

Selection of heating elements

There are only two types of heat sources for an electric floor: heating cables and infrared films. There is a misconception that the film is not used for laying tiles. However, in some situations it can be extremely useful, so consider both options..

The main difference between a cable and a film is that in the first case, heating is carried out exclusively along the laying route, while the film elements radiate heat throughout their entire area. Because of this, when using a cable, a so-called thermal zebra can form – areas with varying degrees of heating, such a defect is especially pronounced in the first minutes after switching on. There are two ways to eliminate the heat zebra: by laying the cable more densely or covering it with a sufficiently thick layer of screed.

Unfortunately, the actual heating temperature of the cable is not limited, and if it is laid too often, the floor will be noticeably hot. This is caused by a pronounced thermal inertia: while the heat sensor is activated, the material adjacent to the cable heats up so much that even after the heaters are turned off, the floor surface temperature will exceed 40–45 ° С, which feels very uncomfortable.

It is also not always possible to arrange a thick screed. According to the requirements of SNiP, the floor level in the bathrooms should be 50 mm below the mark in the adjacent rooms. Unfortunately, at secondary housing objects, the thickness of the screed covering the overlap is scanty, and you still need to arrange waterproofing and install insulation, observe the required thickness of the adhesive seam. In such cases, it is most beneficial to use a film warm floor..

There is no need to worry that the film will interfere with the adhesion of the screed to the heat insulator, in the classical system there is no connection between these two layers, that is, the floor can, in some approximation, be called floating. However, it is also not worth laying the tiles directly on the film: the strength of the screed must provide sufficient rigidity, and the weight of the accumulating layer must be comparable to the throughput loads. Only in this case, the top layer of the warm floor will reliably press the thermal insulation to the rough surface and will not be subject to sagging, respectively, the tile will never move away from it.

Placement of the thermostat

There is a not quite obvious rule – to start the process of installing a warm floor with the choice of a model and a place for installing the thermostat. The statement seems controversial, because the underfloor heating is done before the screed is installed, and the screed itself precedes the electrical installation. Of course, the installation of the thermostat and temperature sensor can be postponed to a later date, however, the place for the thermostat must be determined in advance.

With this procedure, you will not have to break the layout of the heating elements and take care of correctly assembling the electrical equipment. The vast majority of thermostats for underfloor heating are mounted in an installation socket box with an inner diameter of 60 mm. Unlike switches and sockets, this box should be positioned 140–160 cm from the floor for better control. It is better if the thermostat is not located in the bathroom, but in an adjacent room. So it will be possible to turn on the floor heating without going into the bathroom and not turning on the light, and after a few minutes calmly and comfortably start water procedures.

In a niche for an outlet, you need to drill a through hole to bring the wire of the temperature sensor into the bathroom. Further, from the exit point to the floor in the wall, it is necessary to cut a vertical line along which the wire will drop to the floor. Naturally, the place for installing the thermostat must be chosen in such a way that the distance from the projection of the electric point to the nearest heating element is minimal.

The temperature sensor should be installed close to the heating cable or foil. Unlike the underfloor heating film for laminate or linoleum, it is not required to cut the thermal insulation. The temperature probe is placed on top of the foil or pressed against the heating cable with a nylon clamp. But this must be done at the stage of pouring the screed or immediately after laying the heating elements. In advance, you just need to determine the sufficient length of the cables: one two-wire for the temperature sensor and the second three-wire for connecting the heating elements and grounding.

Connection diagram

In the electrical diagram, underfloor heating heaters are marked as resistive loads. The supply voltage can be either 220 V AC or 12 V DC. The latter is typical for the most part for heating films that do not require grounding in fact, at a safe voltage. Thus, two circuit topologies can be distinguished:

1. When powered by mains voltage, a normally open pair of relay contacts of the thermostat is switched on in the phase wire break. In this case, the heating elements and the control device are powered in parallel from the line protected by a 30 mA RCD.
2. When supplied with safe voltage, the thermostat is installed in the break of either of the two wires of the low-voltage network, that is, the secondary circuit of the transformer. In this case, the transformer itself is installed in the technical room, thus, it is required to lay two cables from the switchboard: one for powering the heating elements and one for connecting the thermostat.

Infrared underfloor heating connection diagram: 1 – bitumen insulation; 2 – contact clip; 3 – thermostat; 4 – temperature sensor

When heating a floor area of ​​more than 3 m² it is recommended to install an intermediate contactor, which is valid when supplying both mains and reduced voltage. The relay group of the thermostat is not designed to switch significant loads, even if the manufacturer declares permissible currents of 10 or even 16 amperes. Turning on a warm floor through a contactor does not require serious additional investments, it is enough to supply power according to a three-wire circuit, using a cable with a so-called negative conductor of low cross-section. This core is used to connect to the phase thermostat from the RCD output terminals. The working neutral conductor is removed from the common block without breaking, while the cable is routed through the installation box of the thermostat, for which the zero supply is removed through the piercing clamp. A contactor is installed in the phase conductor break, located in the switchboard. When supplying a warm floor, everything is even simpler: the contactor is simply installed in the break of the load circuit of the transformer.

Connecting an electric underfloor heating through a contactor: 1 – input automatic; 2 – counter; 3 – UZA 30A; 4 – circuit breaker for the contactor; 5 – contactor; 6 – thermostat; 7 – cable heated floor; 8 – temperature sensor; 9 – junction box; 10 – zero bus; 11 – grounding bus

Floor heating installation

So we come to the most interesting part – the installation of a warm floor. Beforehand, preparation of the rough surface must be done: the old screed is removed, large cracks and gaps in the floor are filled with cement mortar. If the curvature of the rough surface exceeds 2 mm per m² or 4 mm on a common plane, preliminary alignment is required. It is performed using the technology of rough plastering, controlling the flatness with a rule of 150 cm length.

A layer of thermal insulation must be laid on the leveled surface. Traditionally, extruded polystyrene foam (XPS) is used for this purpose. For a warm floor in a bathroom, a thickness of 10-15 mm will be enough. To facilitate the implementation of all further operations, it is recommended to fix the insulation plates on the rough surface using a universal tile adhesive. There are a couple more recommendations: use plates with a lock joint at the joints and do not lay thermal insulation under the elements of plumbing and in the areas of furniture placement.

Heating elements are laid on top of the insulation. Different installation technologies apply for cable and foil.

When laying the cable, it is fixed to the base of the floor through the insulation. For these purposes, it is most convenient to use mounting tapes, which are attached to the ceiling with plastic dowels, while the cable is pressed by the bending tape tongues. If the cable has only one core, it is better to lay it in parallel lines, either with a snake or a snail, so that both ends are connected at the beginning of the route. For the installation of a warm floor in the bathroom, only a cable with a grounding braid is suitable.

If a film is used, it can be fixed with disc dowels in places where there are no conductive tracks. 1 m² there must be at least 4–5 fastening points. If the film is powered by mains voltage, a grounded shield – ordinary aluminum foil – is laid on top before fixing it. The joints of the screen must be glued with copper or aluminum tape with a conductive adhesive.

After laying and fixing the heating elements, they must be connected. The cable is connected to the power wires by means of special sealed connectors included in the kit. The film is connected by means of standard piercing clips called crocodiles. In this case, the connection points are pasted over with a special insulating tape..

The cable is grounded with a separate PV-3 wire with a cross section of 4 mm² through a standard connector. The connection of the protective conductor to the foil screen of the film is performed by soldering, the optimum seam length is at least 50 mm. Do not forget to put in place and fix the temperature sensor and the wire with which it is connected. When all of the above is done, you can start pouring the screed and laying the tiles..