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Controlled consumption, homogeneous heat, comfort, space saving... the hot water heating floors are not lacking in assets. First of them: a comfort without equivalent.

How to choose a low temperature heating floor (PCRBT)

With a maximum temperature of 28° C (1979 decree) and room-by-room regulation, the low-temperature hydraulic reversible heating floor (PCRBT) frees the walls. It allows to lower the temperature by 2 or 3° C, which, according to the Ademe *, represents a saving of 15% of the heating bill. Compatible with any type of energy production, it works by radiation by heating the mass and not the air. At 18° C, it provides the same comfort at 20° C produced with other modes of heating.
Reversible, it is also an alternative to air conditioning. In summer, it lowers the temperature from 4 to 6° C in a homogeneous way. For this, however, it is necessary to provide the connection as soon as it is implemented in order to complete it with a refresh system.
* Agency of the Environment and the Energy Management which puts at the disposal of the particular expertise and advice.

Flat or level slabs

The PCRBT consists of an insulator placed on the ground that supports tubes, mainly synthetic materials and more rarely copper. The insulation consists of slabs or plates that can be flat or studs (then forming a recess for the tubes). When flat, the tubes are held by expansion collars (staples) which serve as guidance.
The installation is then distinguished according to the architectural and technical constraints.
As for the principle of operation, it is simple: the water heated by a heat generator (boiler, heat pump or solar collectors) circulates in the network of tubes and warms the room where it is installed like a huge horizontal radiator.

The heat generator

Three types of equipment can be used.

• The boiler at low and very low temperature or, better, with condensation: it allows here a maximum comfort and a gain of about 10% on the consumption of heating, coupled with a system of control and regulation.
• The geothermal heat pump or air / water: when it is reversible, it allows to obtain a comfort all the year (hot winter, cold summer). This type of installation currently represents a high-end solution in a single-family house.
• A solar system: heat from solar thermal collectors is stored in a buffer water tank through a heat exchanger. This water is used for heating the home through the floor.

The coating

Floor covering support, the coating screed has the function of transmitting the heat flow. Properly fabricated coating, low thickness, and high thermal conductivity are critical factors in overall system performance and performance.

There are three processes:

• Sealing mortar: to be used mainly with tiling. Used with a welded mesh reinforcement or fibers, it offers a minimum thickness of 50 mm.
• Concrete coating: it is applied in floating slab, pulled to the ruler and smoothed with the trowel. Its density, floor covering included, must be 160 kg / m² maximum to limit the thermal inertia.
• The fluid screed: anhydrite or cement-based, it is the ideal solution for the coating of the heating network. It also offers a low inertia due to its thin thickness (30 mm above the tubes).

PCRBT: 3 methods of implementation

There are three implementation solutions: wet, dry and semi-dry.
With the first, the system is embedded under a fluid concrete screed on which the flooring is laid. So we add water to the coating (hence its name "wet").
This solution offers a higher calorific value. Originally reserved for the new because of its thickness, it now adapts to renovation with a thinner screed.
The dry solution is more particularly dedicated to renovation. This method consists in placing the tubes in pre-cast channels in the insulation. Added to this is a dry screed consisting of diffusion plates that replace the asphalt concrete. These plates can be made of cellulosic concrete, reinforced gypsum (Fermacell type), or even galvanized sheet steel. They are cut with a circular saw and placed next to each other.
Without slab or flowing screed, the floor here is a slimming cure.
The third solution is to lay the pipes on insulation panels specially studied and partially embedded in the slab (hence its name "semisèche"). The system is based on screed panels for screeds that rest directly on the carrier or on a thermal and / or sound insulation.
The total thickness of the screed is about 30 mm and the system much lighter than a traditional heated floor. The final coating sticks directly on the separating mat, which can be put in place as soon as the screed is accessible to walking.

Heated floor: which floor covering to choose?

In terms of thermal resistance *, tiling is the most suitable floor covering for underfloor heating. It does not include porous coatings with which condensation phenomena may increase, as well as carpets on foam or cork, due to their excessive thermal resistance.
The issue of parquet is quite delicate (even if flooring manufacturers offer compatible floors)... In solid oak, end-timber or on joists, it is not allowed on a heated floor, just as floating floors. Indeed, the air space between the underside of the slats and the heated floor would have much too much thermal resistance. It is also necessary to separate the beech and the flooring to clip. In all cases, the thickness of the floor must not exceed 18 mm.
And the heating pipes must be covered by a minimum of 30 mm thick screed. Its drying must be completed by a temperature rise of the installation (until reaching the temperature of use of 27° C maximum) maintained during three weeks before laying of the parquet floor. The heating is then interrupted for 48 hours before being restarted gradually at least one week after the installation of the parquet.

* For optimum performance of the underfloor heating system, the thermal resistance of the covering must be as low as possible and must not exceed 0.09 m2.K / W.

peripheral band (uncoupling band)

The peripheral strip (uncoupling strip) is intended to isolate the edges of the heating floor of constructive elements, such as walls or partitions, and to ensure the continuity of the insulation throughout the perimeter of the room.

Which coating on the floor heating

The construction site must take into account the flooring installed on the heated floor. Indeed, the thermal resistance between a PVC floor and a wooden floor is far from identical. The spacing between the tubes (called "steps") will also be very different.

Distribution and floor heating

Attention to the distribution nurse

The installation of a floor heating must take into account the location of the nanny.
Indeed, if it is implemented near the boiler for ease, it then becomes necessary to install pipe distribution paths before reaching the rooms to be heated.
This leads to losing any thermal control of the part traversed. If the collector is placed in a garage next to a kitchen (very frequent confi guration), the tubes pass under the wall of separation of the two spaces, cover the whole surface of the kitchen to then connect to the room to be heated: the occupants go usually complain that they do not have control of the power.
It is therefore better to multiply the collectors: two collectors of five circuits each are preferable to only one of ten circuits. Even if the cost of departure is greater, the comfort obtained will be better.

Heating parquet: 6 terms to know

BAO: Oxygen barrier to reduce slugging of heating circuits
PB: polybutene
PE: polyethylene
PERcross-linked polyethylene
PE-RT: high-strength and ultra-flexible polyethylene
PE-XA, XB, XC...: cross-linked polyethylene according to method "A", "B", etc. (There are four different methods of crosslinking).

Certitherm: a mark of quality


Launched two years ago by the National Union of Manufacturers of Components and Integrated Heating, Cooling and Sanitary Systems (Cochebat), the quality mark Certitherm guarantees the efficiency and performance of the system if it is installed in compliance with the rules (standard NF EN 1264).

Comparative table of eight heated floors

This information appeared the first time in System D in January 2014: prices and references may have evolved at the moment of your reading.
Presentation of the eight heated floors

Video Instruction: How to Install DIY Radiant Floor Heating