How to choose thermal insulation for a warm floor: we choose reliable material

What to choose thermal insulation for underfloor heating

The efficiency of any “warm floor” system depends largely on the characteristics of the installed thermal insulation.

It is not only a matter of eliminating energy losses and rational distribution of heat, well-chosen thermal insulation for a warm floor will significantly reduce energy consumption.


  • Functions and specifics of thermal insulation
  • Insulation working in “warm floors”
  • Expanded polystyrene and heating systems
  • Cork insulation for underfloor heating
  • Thermal insulation foil foamed polyethylene

Functions and specifics of thermal insulation

Arrangement of thermal insulation for the “warm floor” system will allow rational use of the received thermal energy: not for heating concrete structures, but directly for floor heating. The choice of electrically insulating material is determined by the choice of insulation technology, the type of flooring, and the particularity of the room where the warm floor will be laid. Extruded polystyrene backing, mineral wool or polystyrene it is used for thermal insulation of a balcony slab, a floor on the ground floor, the thickness of the heat-insulating layer should in this case be at least 50 mm. If the floor is above the heated room, the thickness of the insulation must not be less than 20 mm.

The amount of heat depends on the thickness of the insulation

The dependence of the heat flux up on the thickness of the insulation

Thermal insulation is laid on a concrete floor base, cleaned from dust and debris. If it is supposed to use a heat-insulated floor as the main heating system, then it is advisable to use mechanically strong thermal insulation, with a thickness of 50 mm or more, with the highest heat-insulating characteristics. The thickness of the heat-insulating material used for floors with a heated room below is usually one and a half to two times thinner than that used for arranging floor heating on the basement. Consider the basic requirements for thermal insulation under floor heating.

In addition to a low coefficient of thermal conductivity (0.03-0.05 W / m * K), minimal moisture absorption, good indicators of elasticity and density are important, in order to avoid damage to thermal insulation under the weight of the screed and flooring.

The device of an electric heat-insulated floor of a heat-insulated floor

Electric underfloor heating circuit

In addition to the dense structure, moisture resistance, resistance to the action of fungi and mold, plates of extruded polystyrene are characterized by durability and low thermal conductivity, which, due to the combination of properties, would make this material ideal for arranging thermal insulation if it were not for the ability to release toxic substances during combustion. In addition, this material does not allow air to pass, which is necessary in case of insulation of a wooden floor.

Insulation working in “warm floors”

Expanded polystyrene and heating systems

Most often, as a thermal insulation for a heat-insulated floor, panels or plates made of polystyrene foam or basalt fiber are used. Polystyrene foam boards up to 30 mm thick are divided into sections 1000x166x30 mm, connected by a multilayer foil cloth with mounting marking. It consists of a coating of foam sheets, aluminum coating and a protective overlap. Important properties of polystyrene are the stability of the structure with changes in temperature, moisture resistance, high strength in combination with low density (0.015-0.05 g / cm 3). Polystyrene foam insulation for water floors is characterized by resistance to various kinds of microorganisms, which prevents the possibility of the emergence of rotting bacteria. When heated, thermal insulation from polystyrene foam does not emit harmful substances.

Thin (5-10 mm) foil-coated insulating materials are used when laying a thick insulating layer is not possible. In order to avoid heat loss through the walls, it is mandatory to use a damping tape.

Cork insulation for underfloor heating

Roll of cork insulation

Cork insulation is distinguished by excellent technical qualities, but the activity of the application “slows down” not at an affordable price

Often manufacturers of “warm floor” systems as a heat-insulating material, the use of sheet cork is recommended. Firstly, due to the natural heat-insulating properties of the cork: even with a layer thickness of 2 mm, it effectively retains heat, which will significantly save on electricity consumption.

When pouring concrete, the cork layer does not deform, nor does it change its volume under conditions of temperature difference. The material is environmentally friendly, does not rot and does not burn. The main disadvantage of this material is its high cost..

Thermal insulation foil foamed polyethylene

It is a foiled polyethylene foam. This rolled material is inferior to the cork in thermal conductivity. Polyethylene, being a poor heat insulator, is nevertheless appropriate in the composition of the thermal insulation material penofol due to the ability to form a structure with air bubbles inside. The effectiveness of penofol depends on the thickness. The material tends to crush under the weight of concrete, which leads to a decrease in the effectiveness of the insulator. Compared to cork, penofol loses on this indicator significantly.

Thermal insulation foil foamed polyethylene

Direct contact of foamed polystyrene foam without a laminating coating with a heating cable of electrical systems and with a cement screed is unacceptable

Foil layer – lamination required!

Lamination of the layer on thermal insulation is necessary to exclude the contact of the cement mortar with an insulator, because the cement mortar is, in fact, an aggressive environment that destructively destructs a thin layer of metal (foil). Contact of the heating cable directly with the heat-insulating material may result in damage to the cable sheath due to overheating. Therefore, if the selected insulation material is not laminated, it is advisable to lay polyethylene on top of the foil and only after installing the cable.

To arrange thermal insulation, expanded clay, polystyrene foam, fomisol, foil isolone, etc. can be used. Non-cast material requires mandatory coating with an additional layer of screed, additional use of penofol is possible. The use of sheet foam is not always acceptable (the floor level in this case will rise by 5 cm).