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Preliminaries – laying thermal insulation and filling expansion joints

Thermal insulation in the form of foamed polystyrene boards is laid on the prepared floor base. In first place, EPS 100 expanded polystyrene boards are laid and followed by the Kisan Comfort system polystyrene boards depending on the underfloor heating design. If the surface of the floating screed is to descend, then the required slope must already be shaped in the supporting base so that the screed of the same thickness can be made (according to DIN 18560).


Requirements for dimensions and construction of heating panels according to PN-EN
1264 for wet screeds:
Maximum area of a heating panel < 40 m2
Maximum length of the heating panel’s longer side < 8 m
Maximum ratio of the heating panel’s sides: 1:2


Edge insulation is laid along external and internal walls and in expansion joints designed between    heating panels. If the floor area exceeds 40 m2, it needs to be divided by expansion joints into a few heating panels. Each side of the heating panel may not be longer than 8 m. Expansion joints must run from the insulation course to the floor covering. Heating coil pipes should be laid in such a way so as to reduce pipe passing through expansion joints to the minimum. Connecting pipes crossing an expansion joint should be laid in a protecting tube (corrugated flex nylon conduit) approx. 30 cm long. The ends of the protecting tube should be sealed with a self-adhesive tape to prevent the ingress of mortar to the inside of the protecting tube. In order to control concrete scratching (due to stresses during concrete setting), apparent gaps are made by cutting a notch in concrete with a thin wooden slat and by filling the notch with flexible synthetic resin after the mortar has been dried. The wall tape can be placed over the first course of thermal insulation.




Materiał trwale elastyczny = Permanently flexible material
Taśma przyścienna = Wall tape
Rury = Pipes
Izolacja termiczna = Thermal insulation



The space over the expansion joint should be filled with a permanently flexible material, e.g. synthetic resin (when laying a floor finishing course). The PE film, which is stuck to the wall tape from one side, is turned up against the styrofoam course to prevent the ingress of concrete between thermal insulation and edge insulation. Where the wall tape is placed in an expansion joint then the stuck film is laid on one side of the tape, whereas the gap between the tape and styrofoam on the opposite side should be covered by sealing it with a wide self-adhesive tape.


Laying pipes

Pipes can be laid in two layouts:

a) in the form of meander-shaped heating coil; in this case the beginning of the heating coil with the highest temperature is located by the wall with the highest heat losses;

b) in the form of loop-shaped (bifilar) heating coil resulting in a more regular floor temperature distribution.



Where heat losses are high, through large window and door openings, a 1 m wide edge zone can be used along external walls where the pipes are laid with lesser spacing. A higher floor temperature is allowed in the edge zone.

Usually, the heating coil in the edge zone forms an independent heating circuit. The heating coil in the edge zone in low area spaces is allowed to be connected with the primary loop.



The pipe sections connected to a manifold should be installed in a casing pipe (e.g. corrugated flexible nylon conduit). The length of the casing pipe in the heating panel should be about 1 m, and its end in the panel should be protected against the ingress of mortar to the inside of the casing pipe.



Leak-proof test

Before concrete is poured onto the pipes, the system should be tested for leaks at a pressure of 0.6 MPa within 24 hours. During the concrete setting period (20–28 days), the pipes should be under  pressure of 0.2–0.3 MPa. After the concrete setting period and before laying floor covering, the heating panel should be warmed up.


The system must not be hot started until concrete has been set.


Milestone acceptance

The milestone acceptance of the underfloor heating system should be made in the presence of the investor or its representative. After completing the installation, during the milestone acceptance of the underfloor heating system, the installed materials and equipment should be checked for compliance with the design:

-    thermal insulation and damp insulation performance,
-    expansion joints,
-    heating coils,
-    prepare records for leak proof tests and pressure tests of the underfloor heating system,
-    make sure that the entry regarding the system acceptance is made in the construction log.

Constructing heating panel

The heating panel in the underfloor heating systems designed for residential buildings should have minimum compressive strength and tensile strength of 12 MPa and 3 MPa, respectively. The heating panel of more than 10 cm in thickness is not recommended. In case of underfloor heating intended for other uses, e.g. exhibition and production halls – the heating panel strength must be determined by a designer depending on the facility’s intended use in accordance with PN-EN 13813 standard for making screeds. The heating panel must be made as floating, i.e. it must be separated with edge tape from the building’s structural components. Mortars used for the construction of the heating panel should have consistency ensuring good mortar venting, no air bubbles in the applied course of mortar and complete contact with heating pipes.

Materials and additives

Two types of mortars are used to construct the heating panel:

-    cement mortars,
-    anhydrite mortars.

In order to improve the properties of cement mortars, in particular their plasticity, a plasticizer is added. The amount of batched water depends on the type of the plasticizer used. When added, it reduces the amount of batched water by about 15%, which reduces shrinkage during mortar setting and reduces porosity. Additionally, it speeds up concrete hardening, particularly in the first period, increases   concrete strength by about 15% as compared with matured concretes, improves workability and plasticity of batched concrete mix, improves resistance to water and frost resistance, protects steel in reinforced concrete against corrosion and reduces water absorption even by 50%.

 The Kisan Comfort system plasticizer should be metered in a proportion of 3.05 l per 1 m3 of concrete.


Cement mortars should be made from Portland cement. The aggregate grading of 0–8 mm is required with share of 0–4 mm fraction ≤ 70%. The batched water used for preparing mortars must meet the requirements of applicable standard. Ready-to-use dry mixtures are used as anhydrite mortars for the construction of heating panels.

Constructing heating panel

In order to construct the heating panel from cement mortar, the composition specified in the table below is recommended:


Aggregate grading [mm] 0-8 0-8 0-8
Amount of cement per 1 m3 of concrete [kg/m3] 300-350 375-425 425-475
Water to concrete ratio 0,45 0,55 0,70
Strength [N/mm2] 22,5 30,00 50,00


KISAN recommends the following guidelines to be observed when constructing the heating panel in underfloor water heating:

-    Plasticizer should be used according to the manufacturer’s instructions.
-    The recommended content of cement in the floor should be 320–350 kg/m3.
-    Each batch of concrete should be prepared strictly in accordance with the same prescription relating to aggregate, cement, water and mixing time.
-    Concrete should be mixed until uniform dry plastic non water saturated consistency is obtained.
-     It is not recommended that concrete be applied by using a plastering unit – the work should be done manually.
-    The screed should be protected from walking in the initial period of concrete setting – for a minimum of 7 days.
-    The screed should be watered once a day after 24 hours from its installation for a minimum of 7 days.
-    Concrete should be allowed to cure for 28 days. In this period, the floor must not be loaded mechanically; the room ventilation should be limited by closing window openings so that the heating panel matures in the same conditions across its entire area.
-    Cement of strength class 35 should be used for the heating panel; natural sand and chippings from hard fine-grain rocks should be used as aggregate.
-    The mesh immersed in the screed should have the same dimensions as the expansion joint field (the mesh may not come into contact with the joint filler tape); the ends of wires in the mesh should be bent up to prevent their contact with the pipe surface.



When installing a floor finish:

- The underfloor heating system should be under pressure, in order to detect any possible damages caused during the performance of previous works.

- Do not use sharp objects and hard shoes.


Moreover, when making the heating panel, tightness between the edge tape and damp proof course should be ensured. Mortar may neither penetrate the expansion joint gap nor come into contact with the building’s structural components. Please follow the manufacturer’s instructions when constructing anhydrite heating panels with the use of self-levelling compounds (specially prepared for this purpose).


During the construction of the heating panel water pressure in heating pipes should be 0.2–0.3 MPa.

When pressure remains on a steady level this shows that no damages were caused to heating pipes during the construction of the heating panel.

Start-up and plumbing control of the underfloor heating system

During the start-up period, a feed temperature of 25°C should be maintained for 3 days and then increased by 5°C every day until the maximum temperature is achieved. The system should be commissioned after the mortar setting time has elapsed (20-28 days for concrete and 7 days for anhydrite screed). Under floor heating is characterised by high thermal inertia. This means that after switching it off, the heating panel still gives off heat for a long time. Therefore, there are difficulties in automatic temperature controlling in these rooms where periodical significant heat gains occur, e.g. caused by insolation or process heat gains. The following control methods can be used in underfloor heating: common, individual, based on control modules, self-regulation and fixed set point control.

Assembly instructions

a)    Delivered together with piping materials, the manufacturers’ declarations of conformity are, in accordance with applicable regulations, the basis for the site acceptance test of the underfloor heating systems.
b)    When installing an underfloor heating system, certified materials should be used of the quality ensuring the system’s failure-free operation in the periods between the heavy repairs of the building.
c)    Refer to “Instructions for design and assembly of mechanical services made from the multilayer pipes of the KISAN system” (Instructions 1) for detailed instructions for mounting couplings with KISAN type pipes.
d)    The space over the expansion joint should be filled with a permanently flexible material, e.g. synthetic resin (when laying a floor finishing course).
e)    The system must not be hot started until concrete has been set.
f)    When laying a floor finish:
-    The underfloor heating system should be under pressure, in order to detect any possible damages caused during the performance of previous works.
-    Do not use any sharp objects and hard shoes.
-    After the screed setting period and before laying floor covering, the heating panel should be warmed up.
g)    When pouring the screed, special care should be taken to eliminate the connections of the  heating panels above expansion joints with each other or with the building’s structural components.  The heating panels must be thoroughly separated by expansion joints.