Types of underlay for infrared warm floors and the order of installation

Modern homes are choosing for infrared warm floors more and more because of their even heat distribution and energy efficiency. The underlay is essential to guaranteeing their efficacy because it affects heat retention and system performance as a whole. Knowing the various kinds of underlays on the market will help you select the best one for your requirements and guarantee a cozy and economical heating solution.

There are a few alternatives to take into account when choosing underlays for infrared heated flooring. Every variety offers distinct characteristics and advantages, accommodating varying installation needs and flooring kinds. Your heating system’s efficiency can be greatly affected by the underlay you choose, which ranges from foam and cork to reflective insulation. Making the proper choice is crucial to maximizing warmth and reducing energy loss.

Selecting the appropriate material and correctly installing the underlay are equally crucial. A well-executed installation guarantees that the infrared heat is dispersed uniformly and efficiently throughout the space. The procedure entails meticulous setup, accurate positioning, and snug fitting to prevent any openings or misalignments that might impair the system’s functionality.

This post will examine the different kinds of underlays that work well with infrared heated floors, outlining their benefits and ideal applications. To help you get the best results and take full advantage of your infrared heating system, we’ll also provide you a step-by-step installation guide.

Type of Underlay Order of Installation
Foam Underlay Lay the foam underlay on a clean, level surface. Ensure it covers the entire area where the infrared warm floor will be installed. Secure with tape if necessary.
Reflective Foil Underlay Place the reflective foil underlay shiny side up on the floor. Overlap the edges by a few inches and secure them with tape. This layer helps to reflect heat upwards.
Foam and Foil Combined Underlay Roll out the combined underlay on the prepared floor surface. Make sure the foil side is facing up to reflect heat. Tape the seams to keep it in place.
Cork Underlay Unroll the cork underlay and cut it to fit the space. Lay it flat on the floor, ensuring there are no gaps. Secure it with adhesive tape if needed.

Needed or not?

An urgent concern during the heating season is heat preservation. Some install sealed double-glazed windows, some seal their windows, and some install underfloor heating. The latter needs to be supported by a heat-reflecting material, regardless of the heating system being used.

Not everyone is aware of the necessity of it. The entire idea is that heat has a tendency to move to the sides and up and down. If it is left unattended, it will leak, which will prevent the room from receiving the necessary amount of heating and result in higher utility bills. The purpose of the backing is to accurately reflect heat in the desired direction. For instance, it’s crucial that heat from a warm infrared floor in an apartment does not "go away" and warm the ceilings of the neighbors below it, or, if the apartment is on the first floor, into the basement.

You should take into account the power of the infrared film, the density and thickness of the finish coating, and the substrate material’s thermal reflection coefficient in order to minimize heating and obtain adequate heat.

Selecting a substrate will be made simpler by combining all of the warm floor’s parameters.

Is it possible to do without it?

It is not permissible to set up IR systems in private homes using substrate. In the event that, for instance, a children’s game room is situated beneath a second-floor bedroom, heat will transfer to a concrete overlap between the two without a substrate.

In this scenario, the room’s floor and ceiling will both be heated, though professionals do not suggest laying such a floor without a substrate. It serves other purposes in addition to retaining heat.

The device can operate at full power, but if there’s no need to heat the black overlap, the heat will just dissipate in the absence of a substrate, leaving the room where the IR film is mounted cool.

Requirements for film

Not all substrates are appropriate for iK film. She has to possess the following qualities in order for it to satisfy the requirements:

  • Thickness from 4 mm and more. This indicator is very important, since grooves are made in the substrate for laying wires and a temperature sensor. If you simply put them on the surface of the film, then over time under pressure on the finish coating they will be damaged, which can lead to either a short circuit, or to the occurrence of sparks, or to a fire.
  • Absence of a metallized layer. There are substrates with conductive properties, that is, with a side made of aluminum foil. Such material is not suitable for IR film floors, since it is capable of accumulating static electricity. The latter will “manifest” itself in the form of crackling, noise and weak, but unpleasant electric discharges. In order for the substrate to meet the requirements of IR underfloor heating, it must have a reflective, but not foil layer.
  • Waterproofing properties. No matter how high-quality the subfloor is, it can pass or release moisture. To prevent it from coming into contact with the electrical contacts of the IR film, waterproofing is needed.
  • Unchanged proportions. The substrate should not shrink under the influence of heat. If this happens, the integrity of the warm floor and the finishing coating will be damaged. Therefore, it is important to take into account such a parameter as resistance to high temperatures.
  • Resistance to deformation. The minimum service life of an IR film floor is 10-15 years. It is important that during this time the substrate does not deform under the influence of temperature changes and external loads on the floor.
  • Environmental safety. The material should not emit harmful substances when heated, otherwise over time the impact of the latter on people will lead to health problems.

Leveling the subfloor’s surface is one of the substrate’s other uses. It covers up its flaws and evens out small height disparities.

Types for IR systems

The Russian market offers an enormous variety of substrate materials, but not all of them work well with warm infrared flooring. The most common underlay types that professionals suggest using when laying a warm floor pie are listed below.

EPPS

The benefits of extruded polystyrene foam are as follows:

  • high level of moisture protection;
  • low density;
  • has closed cells, due to which the material has a high degree of thermal conductivity;
  • noise absorption level – 23 dB;
  • impact strength 0.035 W / m 2;
  • bending resistance 0.25 MPa;
  • does not lose its properties at temperatures from -50 ° C to +75 ° C;
  • safe;
  • low weight of the material;
  • easy installation.

Among the drawbacks, we can mention:

  • the thickness of the material is not able to eliminate differences in height, therefore it is not suitable as a leveling layer and requires a perfectly flat rough base;
  • easily flammable.

Either 50 cm long, 100 cm wide, and 2–5 mm thick slabs or rolls measuring 15 m long, 110 cm wide, and 2 mm thick are available for purchase.

Magnesite sheets

Expanded volcanic perlite, fiberglass (a reinforced layer), and caustic magnesite serve as the foundation for this material. The following are some benefits of using magnesium glass sheets as a substrate:

  • high resistance to moisture;
  • degree of deformation 0.34%;
  • environmental Safety;
  • natural ingredients;
  • does not burn;
  • weighs little;
  • easy to install;
  • high strength;
  • sheet thickness can be from 3 mm to 30 mm;
  • service life up to 50 years.

Among the drawbacks is its expense:

If the rough base is uneven, this material can be used as a substrate beneath an IR floor. Despite their flexibility, the slabs are strong enough to cover up any flaws in the subfloor.

Fiberboard

In addition to being used as a substrate, hardboard is also used to make furniture, interior doors, partitions, and a variety of other items. It is selected for the base beneath the film floor because of the following benefits:

  • resistance to deformation;
  • light weight;
  • easy installation;
  • high strength;
  • heat and sound insulation properties;
  • easy processing.

A fiberboard board can have the following dimensions: 5.5 m for length, 1.5–2 m for width, and 2.5–6 mm for thickness. The material’s drawbacks include flammability and moisture susceptibility; fiberboards swell when the final board has an effect on them. If laminate or tiles are to be placed on top of the film floor, this material needs to be used as a substrate.

Penofol

This kind of foil-covered foamed polyethylene insulation is reflective and thermally stable. Penofol is available in three forms:

  • "A" – the foil layer is located on one side;
  • "B" – the foil layer is applied to both sides of the material;
  • "C" – one layer is foiled, and the other has a self-adhesive surface.

This material should be used carefully as a substrate for the infrared floor because it contains aluminum foil, which allows electricity to pass through. Make sure the wiring is of good quality and that the terminals and wires are connected to the film.

Among the benefits of the material are the following:

  • flexibility, which ensures ease of installation;
  • small thickness;
  • high thermal insulation;
  • moisture resistance;
  • fire safety;
  • noise and waterproofing properties;
  • ease of transportation;
  • affordable price.

Two of the material’s drawbacks are its softness and conductivity.

Lavsan

The basis of this material is foamed polyethylene coated in lavsan. It is regarded by many experts as the ideal substrate type, particularly for infrared underfloor heating. This is because of its benefits, which include:

  • low thermal conductivity;
  • high sound insulation;
  • safety – prevents short circuits when contacts or wires in the IR film are damaged;
  • tensile strength;
  • resistance to aggressive substances;
  • protection from steam and moisture.

Because it doesn’t sag when it comes into contact with concrete, this kind of substrate can be used for screeds as well as underfloor heating installations.

The technical specifications of this material are listed below:

There are no drawbacks to this material, particularly when utilized as an IR film floor substrate.

Cork

Since it absorbs moisture, this natural material has been used as a substrate for a long time—but only in dry rooms. Principal Benefits of Using Cork Substrates to Apply IR Film:

  • strength;
  • resistance to deformation: even with increased pressure on it, the plug returns to its original state as soon as the load disappears;
  • good level of heat and noise insulation;
  • easy to install;
  • sold in rolls and slabs;
  • fungi and mold do not form in it;
  • long service life.

High cost and poor resistance to moisture are drawbacks. Thus, 10 m long, 1 m wide, and 4 mm thick rolls will set you back 7,000 rubles each.

Izolon

This is polyethylene foam with closed cells. Isolon comes in two varieties: cross-linked and non-cross-linked. In contrast to the first, where the molecules were "cross-linked," the latter is based on foamed polyethylene, whose molecules have not changed. When used as underlay with infrared (IR) underfloor heating, a cross-linked isolon type with two layers—one made of foamed polyethylene and the other of metallized lavsan film—is appropriate.

Benefits of the content:

  • vapor barrier properties;
  • retains heat well (thermal conductivity coefficient 0.036 W/m °C) and has sufficient density (33 kg/m³);
  • protects against impact noise;
  • high moisture protection;
  • resistance to aggressive substances;
  • hygienically and environmentally safe;
  • light weight;
  • easy to install;
  • service life is 30 years;
  • resistant to rotting;
  • affordable (250 rubles./m2).

This material has a negligible thickness and a high strength to temperature change because of the cross-linked molecules.

Chips on the choice

When selecting the material for such a floor, the following factors should be taken into account:

  • The quality of the draft base. If there is no desire to spend money and time on the leveling screed, then you should choose a substrate that will hide the defects of the draft floor.
  • Finish coating. When laying a heating film under a laminate or tile, you need to give preference to materials with shock-absorbing properties or resistance to deformation. If the finishing coating is soft, such as linoleum or carpet, the underlay must be highly rigid to withstand loads and pressure.
  • Reflective properties. The higher the level of heat reflection, the greater the energy savings.
  • Presence/absence of an aluminum foil layer. Aluminum transmits current, so it is undesirable to use foil made of it when laying electric floors, but such a substrate can be laid directly on the screed so that it reflects heat towards the finishing coating, and under the IR film, use a material without aluminum foil on the side.
  • What will the underfloor heating cake consist of. For example, below is an option using isolon, as well as other materials included in its composition:

Watch the video below to find out more about selecting a substrate for an infrared floor:

Features of installation

Roll and sheet types are the primary differences in installation, regardless of the substrate’s composition. You must be aware of this:

  • slabs are laid end to end and fixed with dowels, glue or staples;
  • roll material is also laid end to end, but the sheets are fixed with construction tape;
  • cork substrates cannot be laid close to the walls to avoid possible moisture penetration, due to which they will swell and lose their shape;
  • the reflective surface of the material should be directed towards the finish coating to avoid loss of heat flows;
  • the side of the film with heating elements should be laid directly on the reflective part of the substrate, which will direct the heat upward.

For infrared underfloor heating, the substrate of choice needs to be thick enough to fit the temperature sensor and contacts. That’s why you need to mark the locations of the grooves after the material is installed.

Skilled artisans do not depend solely on the substrate’s thickness; instead, they create a groove in the concrete screed that completely "drowns" the temperature sensor and terminals. This way, the load from walking on the finish coating is eliminated.

Selecting the appropriate underlay is essential for optimum performance and energy efficiency when installing infrared warm floors. Underlays come in a variety of forms, including foam, cork, and polyethylene. Each type has unique advantages, such as soundproofing, moisture resistance, and insulation. It’s crucial to adhere to a step-by-step procedure to guarantee correct installation: prep the subfloor, install the underlay, make sure it’s securely fastened, and then install the infrared heating film. You can extend the life and efficacy of your infrared warm floor system by choosing the right underlay and following the installation instructions.

Errors and difficulties

Generally speaking, even a novice can install the substrate, but errors can occasionally be made that are challenging to fix. Thus, among them:

  • incorrect calculation of materials;
  • use of a substrate with an aluminum foil layer;
  • overlapping installation of the roll web;
  • laying the substrate with the reflective part down, that is, towards the subfloor;
  • use of material less than 4 mm thick;
  • installation of the substrate only under the IR film, which is unacceptable, since it must be laid over the entire floor area, otherwise there will be differences in height, which will affect the installation of the finishing coating.

Selecting the appropriate underlay for your infrared heated floor is essential to guaranteeing its effectiveness and durability. There are several kinds of underlays out there, such as foam, cork, and reflective foil. There are advantages to each type, including better insulation, noise reduction, and heat distribution. Foam offers both thermal and cushioning qualities, cork acts as a natural insulator, and reflective foil is great at directing heat upward.

It’s also crucial to correctly install the underlay. Start by making sure the subfloor is smooth and clear of debris by cleaning and preparing it. After cutting the underlay to fit the dimensions of the room, lay it out over the whole floor. Be sure to allow for some expansion by leaving a tiny space at the edges. Using glue or adhesive tape, depending on the material and the manufacturer’s instructions, firmly attach the underlay into place.

You can start installing the infrared heating mats after the underlay is put in place. Carefully follow the manufacturer’s instructions to install the thermostat and connect the heating elements. Before covering the mats with the flooring material of your choice, make sure the system is operating properly by testing it once the mats are in place. This methodical process guarantees that your infrared heated floor runs well and creates a cozy, warm atmosphere.

Video on the topic

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Andrey Ivanov

Experienced civil engineer with more than 20 years of experience. Specializing in the construction of industrial and civil facilities. Author of many publications in professional journals.

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