Surface heating, as the name itself indicates, is heating with the use of a surface. Subfloor heating is a well-known example of surface heating. Thermal energy is accumulated in mass concrete, which then transfers it to the room. Surface heating is characterized by a different method of heat release. As opposed to convective systems (radiators), the heat is transferred without using air, such as, for example, the sun, a fireplace, tile furnace or a campfire.
Subfloor heating belongs to the family of surface heating systems, which means that it releases heat as a result of thermal radiation. However, the placement of the subfloor heating system makes it become an enormous air convector anyway. Warm air heated at the floor level rises; thus, subfloor heating uses both forms - convection and radiation. Standard radiators also release some of their energy as a result of radiation, but they are mostly used to heat the air.
First of all, 3THERMO radiators are concealed radiators, so they cannot be seen; they do not hang on a wall but are a part of it. Ordinary hanging radiators are actually air blowers. It is ingenious as they use the principles of physics to draw in cold air and blow out warm air after being heated without a fan. 3 THERMO radiators do not heat the air; this is the main difference.
Heating with warm air is not a healthy form of heat redistribution. We know this, but the convenience of using hanging heaters as compared, for example, to a tile furnace or a fireplace is so great that they have become the main heating system and have replaced old-fashioned forms. At present, as a healthy lifestyle is being promoted and new technological opportunities appear, especially in the area of control and energy management, they are back in style. A 3THERMO concealed radiator reminds one more of a tile furnace than a radiator - but it is more like a tile furnace that has been cut in slices and distributed over the wall. But in this way, we achieve perfect temperature distribution as opposed to a fireplace or a furnace standing somewhere in the corner.
3THERMO is the return to proven forms of heating but in a modern and easy form.
This is a solution similar to subfloor heating. Tubes with water can be also arranged on the wall, not just within the floor. Such a solution is much better for many reasons.
- Firstly, the vertical system of walls, as compared to the horizontal system of the floor, allows for more efficient use of heat emission (radiation) than convection (air movement). The less energy we use to heat the air, the less energy we lose. The air is a very poor heat accumulator (it does not have accumulative capabilities like, for example a solid form, stone, concrete etc.) and it rises quickly looking for a “way out”. Heating with a radiator involves the constant blowing of warm air, and after the heater is turned off, the temperature in the room falls very quickly. In wall heating, all of the energy reaches the wall and heats it. The wall accumulates this heat just like the floor heating system.
- Secondly, heating systems should be installed in places where most heat is lost. This is why radiators are hung under windows. The floor is definitely not the partition where the greatest losses are generated. External walls and roofs are such partitions. Wall heating makes up for heat losses (balances them) where they arise. Due to the accumulative capacity of solids, it is much cheaper to heat a partition than to continuously blow warm air into the room.
- Thirdly, the health aspect. Heated air is a good place for bacteria, and air convection (movement) makes it easier for them to spread throughout the house. Additionally, warm and humid air releases its moisture into cold walls, so our skin is dry and the walls are moist and thus susceptible to fungus attack.
A completely reverse phenomenon occurs in wall heating - the warm wall releases heat into the cooler room without air movement and changes in its ionization and humidity.
If wall heating has so many advantages, why there are so few wall-heating systems?
Well, the existing technological solutions have not promoted this form of heating. The introduction of a tube with water under the plaster required the use of special plasters (otherwise, they would crack). It also made it necessary to use a very thick layer of plaster. Considering contact with the electrical system in the walls and the fact that it was easy to damage the system, few people decided to use this form of heating despite its obvious advantages. The installation itself was another important problem - while the arrangement of tubes is time-consuming, however, most installers were not able to perform the appropriate de-aeration of the system.
On the other hand, electricity-based systems generated an electromagnetic field and attracted charges together with dust, which resulted in the formation of “prints” on the wall, indicating the heating cable routing. Modern 3THERMO concealed heaters eliminate 100% of all of the aforementioned problems; they are very easy to install, are safe even if a failure occurs and they do not generate a magnetic field.
As for the popularity itself, few people know that wall heating was one of the oldest forms of heating. It has been used at least since the 4th century B.C. Unfortunately, our ancestors were not using 3THERMO radiators but a means of special hollow bricks through which hot air was distributed from furnaces placed under the floor.
The structure of the radiator separates the hydraulic system from the radiator. Water does not take part in heat transport under the plaster. Damage to walls and also to the radiator does not cause a hydraulic failure of the central heating system. Other radiators still operate and there is no water leakage. The surface area of the hydraulic system, as compared to the surface area of the heating component, does not exceed 2%, so the probability of the occurrence of a failure is reduced to a minimum. We will improve this parameter only when we launch electronic concealed radiators.
Contrary to what we think about the nature of heat, it works in the following way: it always moves from the higher (warmer) potential to the lower (colder) one; it chooses the simplest way acting in all directions. It is accumulated in solids, dispersed in gaseous states (liquid is an intermediate system).
A failure to understand its nature results from the conviction that heat and warm air are the same. Only warm air goes up. Heat as energy corresponds to the nature of light more and since light can shine from top to bottom; heating is certainly possible in this way.
Regardless of the type of heat emission, whether it occurs as a result of warm air movement (blowers, heaters, convectors) or by thermal radiation (tile furnaces, chimneys, radiators, floor heating), the heat gets out through partitions, which separate us from the cold (external walls, the roof).
It is not very important whether heat is generated in the wall or 2cm from the wall. However, heat generated in the wall (concealed radiators) does not escape together with the air (chimney losses) but it is accumulated. Thermal insulation of the partition is mostly responsible for preventing the heat from getting outside. In this case, wall heating is a positive phenomenon as a dry wall is a much poorer conductor (it constitutes greater resistance for escaping heat) than a wet one.
Economically, there is no better system than surface heating in external partitions. The fact that they were not so popular results mostly from technological limitations and the predominance of radiators on the heating market.
Somebody must be first. Most likely, the idea will catch on, and soon we will hear about other designs of concealed radiators; it is certainly only a matter of time and there is the possibility of patent protection. The market is too large for us to be able to keep the status as the only manufacturer.
The entire radiator is made of an aluminium alloy. Even a relatively aggressive alkaline environment contained in the cement mortar does not have a destructive influence on this aluminium alloy. The radiator itself does not have any movable parts. If it was manufactured correctly, without defects, it is a practically everlasting installation.
The 3THERMO-concealed heater was designed as an open system. The nipple-type water connection can also be used with pex and alu-pex installations. However, the use of an installation that does not belong to the original system will limit your warranty.
System insulated rubber tube (SIRK) was specially selected for our radiators. It does not have linear thermal expansion, dampens noise and hydraulic noise as well as a high heating resistance (does not lose heat during transport). It will never delaminate, even under the influence of high temperatures (as opposed to polymer tubes); it does not become rinsed like copper or brass and does not become rusty like steel pipes. It does not require the use of elbows as it is an elastic duct; it cannot be broken or crushed, and when deformed, it goes back to its original shape.
The rubber EPDM is characterized by proven chemical stability for 50 years. It does not evaporate like PVC or does not corrode. In addition, it is a natural and ecological material as opposed to polymer products.
To put it simply, the clamping ring is a form of manual clamping, typical of this type of rubber systems. Plumbers do not know this system, as it was not used in central heating systems previously, just like the PVC tubing system was not known earlier. Each installation has its own system of connections adapted to its physical properties.
For the 3THERMO tube, a stainless steel ring is used. Clamping is an irreversible process.
It is not the type of rubber hose that we use in our gardens but a rubber EPDM tube. The system insulated rubber tube (SIRK) does not have linear thermal expansion. It dampens noise and hydraulic noise and has high heating resistance (does not lose heat during transport). It will never delaminate, even under the influence of high temperatures (its working temperatures range from -35°C to 145°C); it is not rinsed, has proven chemical stability, does not evaporate or become rusty. It does not require the use of elbows, as it is elastic. It cannot be broken or crushed, and when deformed, it goes back to its original shape. It can be easily installed even at ambient temperatures as low as -10°C.
The rubber tube was selected so as to ensure an invariable hydraulic flow together with a 3THERMO concealed heater.
The selection chart for the concealed radiator can be found at the website in the download tab. The heater capacity depends on the supply temperature, the flow temperature and the heating resistance of the mass in which the radiator is placed.
Due to a very broad range of operation, the radiator can be selected in a surface low-temperature system as well as in a surface “point” high-temperature system (max. 100°C).
At present, European Union countries are moving away from high-temperature systems, which are considered to be not very economical and environmentally unsound. Apart from this, while designing a heating system, one needs to make sure that it is as comfortable as possible, which is related to the even distribution of temperatures.
Both types of heating belong to the family of surface systems, and as such, they have an advantage over convective systems. However, the wall system has an additional advantage, as it balances heat losses where they occur, and the greatest heat losses occur in external walls and not in the floor. In this way, it is the wall system that has the most even heat distribution and not the subfloor heating. Generally, in the subfloor system, the further away from the external wall it is, the warmer it becomes. To make up for this effect, a well-designed subfloor system must take into account the density of the tube arrangement from the external walls.
Additionally, considering the Koenig diagram, we can use the dependence it indicates and reduce the air temperature without losing thermal comfort.
To decide on this, we would need to establish the ranking of priorities, i.e. what is the most important for us. Is it health or the rate of system operation, etc. Generally, at present there is no better heating system than the surface system. Unfortunately, it cannot be used everywhere. It is not appropriate for heating tents: the blower-heating system is definitely the best in this case. A surface radiator will never have such a high capacity as a radiator installed on the wall, and where there is not enough room, it can be the only alternative.
However, with regard to the aspect of health, the 3THERMO heater is irreplaceable.
Absolutely not, never. It is like wearing a warm sweater over a waterproof jacket; it does not make any sense. I understand where these opinions come from, even on expert discussion forums; however, wall heating should be looked at from a slightly broader perspective. One should consider other aspects, not only heat capacity. The heating capacity will indeed be improved when the wall is insulated; however, we will eliminate the natural capacity to regulate the moisture content. The wall has a certain capacity both with regard to heat and moisture. For the wall system, this is a part of the self-regulation system. If we separate it by using insulation, we will eliminate it. In this case, the system will require continuous mechanical ventilation. It will also have a considerable influence on the shift of the water vapour condensation point from the outside towards the centre of the wall.
A wall in which water condenses is a sick wall with reduced durability and a tendency for fungus and mould formation. The only insulation that makes sense is good external insulation, preferably from wool and not Styrofoam, but this is completely different topic.
A well-designed and properly installed wall-heating unit basically has no flaws. In the low-temperature system, i.e. one with a large heating area, the issue of furniture arrangement by the wall also becomes insignificant. The energy which partially covered, e.g. by a wardrobe, does not disappear and still is an element separating from external factors. If wall heating is constructed using 3THERMO concealed radiators, we eliminate one defect, i.e. damaging the tube with water. 3THERMO radiators do not introduce water under the plaster as the temperature is distributed by the radiator itself without the use of water.
We can achieve any temperatures, the 3THERMO radiators, or simply wall heating, do not have any limitations in this respect. However, due to completely different phenomena, other than the convective heating systems that we know, we can reduce the air temperature in the room without compromising comfort. This is possible as the loss of heat is supplemented where it occurs, i.e. in the external wall. For this reason, we do not have to overheat the system to balance thermal differences. It is a very important point due to two aspects: health and economics. Firstly, it is healthier when we breathe in cooler air with natural humidity; secondly, it is cheaper when we do not have to increase the temperature so much. Reducing the temperature by only 1oC means reducing energy consumption by approx. 5-7% (depending on the degree of thermal permeability of the partition).
The design is closely related to responsibility. So, if we want somebody to be liable for our badly-designed heating, for example, we should buy an individual discipline design as the central heating system. For private developments (single-family) houses, executive designs for central heating systems are rarely encountered.
As this is not very important for radiators in which the plumber selects using approximate values, this can have specific consequences for subfloor heating. The thickness of subfloor heating and distances between the tubes differ; however, it is most important to establish our heat loss balance for individual rooms in the building. If this is not selected properly, the only thing we can do is to increase the supply temperature, which is limited to 35oC for subfloor heating for health reasons.
Wall heating systems, including 3THERMO, do not have such limitations. However, saving a poor design by using higher temperatures will mean higher costs of operation.
There are no limitations of the external wall surface temperature with wall heating. Using average temperatures of heating water for low-temperature systems of 25°C to 55°C, the surface wall temperature will range from 23°C to 45°C. Higher supply temperatures are reserved for point wall heating systems, something that looks like a modern tile furnace.
For concealed radiators, as opposed to water-based heating systems using tubes with water, no high stresses are induced. As a result, they do not require thick or special elastic plasters. Any typical type of plaster can be used. 3THERMO radiators can be even installed in a layer of adhesive under ceramic tiles, e.g. in the bathroom.
If plasterboards are used on the wall, the use of a single wall is recommended. Two layers of plasterboard require a design to calculate and take into account additional heat resistance.
For high-temperature supply, the recommendations from the manufacturers of the adhesive and plaster must be taken into consideration with regard to the maximum temperature.
3THERMO wall heating is cheaper in operation than any other wall heating system, based on a typical tube with water. The differences are not very big (approx. 5%), and they mostly result from the differences in flow resistance and the water volume level. However, each wall heating system is better in operating terms than the floor heating by approx. 10-15%, as it is possible to reduce the air temperature and increase the thermal insulation properties of the partition. With regard to convective systems, we estimate the reduction of heating costs at 40%.
There are no such limitations. The only limitation is the space available for a 170cm x 60cm module. One should also remember about the general installation principle, according to which we install radiators on external walls. However, if there is not enough free space on external walls, we can supplement the system by installing radiators on internal walls.
It is easiest to explain this in the following way: A person is like a furnace with a constant temperature of 36.6oC. Heat always “moves” from a warmer body to a colder one. When we stand in front of a cold wall with a temperature of 16oC, our body wants to heat the wall and gives its thermal energy to it. We perceive it as thermal discomfort.
In the opposite situation, on the other hand, when the temperature of the wall is equal to or higher than the temperature of our body, we will never feel a loss of our own heat.
Thermal comfort does not depend on the air temperature in this case, which in convective systems (based on radiators), there must be compensation for the differences that have occurred and supplement them by blowing warm air over us.
The elimination of this phenomenon means savings on the so-called stack losses and an enormous added value to our health and well-being. We feel different when we can breathe in cooler air with natural humidity than when we breathe in air that is too dry. Additionally, we eliminated the movement of dust, allergens, mites etc.
Concealed radiators are compatible with any source. Anything that will cause warm water to flow through the collector is enough; it can be a fireplace with a water jacket. Due to a low volume of water, it is perfect for connecting with a heat pump.
In the future, 3THERMO radiators will be supplied directly by low-power heaters; this will eliminate hydraulic solutions completely and the necessity of building chimney ducts. Considering the development of household renewable energy sources, they can be a very interesting alternative.
The basic advantage is the possibility of using any floor. Another more important advantage is the radiator installation, exactly where heat losses are generated, and also the best temperature distribution and actual possibility of reducing the air temperature in the room without thermal discomfort. Apart from this - the safety of the system - there is a minimized probability of damage to the hydraulic installation. Lower operating costs, easier installation and control of the system.
- 30. Should central heating installation (SIRK) be covered with plaster together with the concealed radiator?
We recommend installing the radiator and covering it with plaster without the mounted installation. After plastering, covering plugs should be removed from the collector nipple connections and the system tube should be installed. The central heating installation together with the lower collector of the concealed radiator should be situated in the floor layer not in the plaster. There will likely be construction sites where it will be necessary to cover the installation with plaster; however, in this case, I would recommend making a groove for the installation and letting the collector “hide” it in the wall.
For the dry plasterboard system, installation should be performed before covering the radiator with the plasterboard.
Don't worry. The radiator weighs less than 1.5 kg. Clips - mounting brackets are used only for hanging the radiator on the wall before plastering. After applying the plaster on the wall, the radiator will bind with it and will be an element of the additional plaster structure. The radiator mesh is modelled on Rabitz mesh which has been used in the construction sector for years.
We sell our products through sales branches, distribution points or directly through Certified Installers.
We provide a 20-year warranty for the designed 3THERMO system on the condition that it is installed by a Certified Installer.
At present, 3THERMO concealed radiators are a water system with a separated hydraulic part in the horizontal section (the floor) and the vertical heating section (the wall).
Warm water flowing through the hydraulic part of the system releases heat to the radiator situated under the plaster. However, a fully electric version (Electric Line) is being developed. We will certainly inform you about introducing this product on our website.
No streaks or stains will ever appear on the wall! The wall can be painted when the colour fades or when you get bored with it, but never because of the installed 3THERMO radiators!
Streaks on the walls apply only to electrical systems. The current flowing through the heating duct generated an electromagnetic field, which attracted charges and dust. Such a phenomenon may not occur in 3THERMO heaters as they provide heat by means of a radiator and not an electric resistance duct.
The 3THERMO-concealed radiator can be supplied to a maximum temperature of 100oC. Depending on the conditions and power consumption, the wall temperature will certainly range from 60 to 90oC. However, nothing justifies the use of such high temperatures, unless we want to have a tile furnace effect on the wall. However, such high parameters of operation will involve considerable energy losses. The system will not be comfortable or economical. We do not know the heat capacity for 100oC, but we can suppose that it will be approx. 500W/m2.
Mostly water systems were responsible for the phenomenon of plaster cracking. This was probably caused by thick layers of plaster (3-5 cm) which were needed to cover water tubes and, secondly, due to the polymer expansion under the influence of the temperature. Polymer hoses used in the wall systems were characterized by very high linear expansion and, as a result, they caused stresses in the plaster. Plaster manufacturers introduced temperature limits, which were supposed to prevent cracking. Others introduced special plasters with the added mixture of perlite and other substances, which made the material more elastic. However, such mixes are characterized by additional heating resistance, which reduces power consumption in the system and are much more expensive. 3THERMO radiators are made, among other things, of the Rabitz mesh, which further strengthens the plaster and the radiator itself is not characterized by significant linear expansion.
- 38. How is it possible that the 3THERMO radiator transfers the water temperature to a height of 1.7 m without any losses? It is physically impossible! Is this perpetuum mobile?
Indeed, the loss is even desired, as it is the loss (the amount of released heat) that determines the capacity of the system. If the radiator did not release (did not lose) the heat collected from water, it could not be a radiator used for heating.
But the heating system itself (radiator) in an insulated environment (without any losses) will transfer exactly the same preset temperature to the very top of its structure (1.7 m) with continuous supplementation (water must have a constant temperature and supply the system all the time). It is as possible as transporting a temperature in a tube with water to a height of 1.7 m (in an insulated environment). Actually... at such a short distance, it is even possible in an uninsulated environment; it is enough to choose a sufficient flow, and the loss will not be detected by basic equipment.
The ability to release heat by the system always depends on the size of the surface area of the system. The radiator increases the surface area (1.6dm2) of an aluminium tube (phi 12mm) through which warm water flows many times. The mesh itself of the 3THERMO radiator provides approx. 350dm2 of heating surface. Therefore, from a linear metre of subfloor heating tube (5dm2) we will obtain 5-10W, and from the 3THERMO radiator (i.e. 0.43 linear metre of the tube) - 200W. Unfortunately, this is not magic but only simple physics confirmed by mathematics.
It can be used, as it is an elastic plaster specially designed to prevent contractions of the material. It must be used for wall heating systems with water pipes. It is not necessary for 3THERMO.
It should also be remembered that elastic plaster means a lower capacity and thermal conductance - precisely 0.3W/mK. For typical mineral plaster, this coefficient is 0.8W/mK, so it will work much better for heat collection and conduction.
The basic difference between the floor and wall heating systems lies in the transmission of heat (although both of them are surface heating systems). In floor heating, similarly to heaters, a stream of heat energy with the air flows towards a cold external wall. In the case, the wall absorbs not only heat energy, but also humidity from the air. The process dries the air in the room and increases humidity of the building envelope. It is only wall heating that can reverse the process. For that reason, overdrying of the air never occurs, which is extremely important to us, users, for health reasons. Relative humidity range for a human amounts to 40 to 60%. A dry wall means the lack of potentially occurring moulds and fungi which are very dangerous to the health. Furthermore, wall heating shifts water steam condensation point outside the wall, thus excluding freezing and improving the wall quality and its thermal insulation capacities.
An additional difference is posed by lower inertia of wall heating systems resulting from lower heating resistance of the wall and a precise prevention of heat losses, directly at the place of their occurrence. Let us examine a situation when a floor heating system must be switched off because of a fast increase of external temperature (on a very sunny winter day). The floor will not emit the accumulated energy very fast, and in addition, solar energy will be absorbed by external walls and rooms with glazed surfaces (windows, etc.) We will have to divert excessive heat energy by ourselves, by opening the windows, thus removing heat produced at our own cost. In case of a wall, additional solar energy will not add up to the energy we have provided since the wall heating capacity is limited.
The wall heating system creates an active thermal barrier and does not cause the outside emission of the building internal heating energy, since the environment (external wall) temperature is higher than the air temperature. The air has no point of cooling or transferring its heat energy. No flow of energy means stable and uniform temperature distribution, which translates into a very high thermal comfort. There is no necessity of compensating for heat losses inside the room to achieve a similar thermal impression and we do not have to maintain high temperature of the air; it may even be lower by 2 to 3 degrees Celsius. However, using the same argument (on the lowering of the air temperature inside a room) for floor heating systems is untrue! As every surface heating system, they are only capable of lowering the supply temperature. For this reason, surface heating systems are frequently called low-temperature heating systems.
Wall heating mounted to internal (partition) walls acts identical to the floor system; similarly, a surface accumulates energy in the mass of concrete (a solid body) and emits it to a cooler environment towards a cool external wall.
Additionally, an important feature of 3THERMO wall heating is the transport of heat energy inside the wall without consuming additional electric energy (forcing the upward flow of water). In case of 2THERMO energy is distributed dry, by means of a radiator. This additionally contributes to higher hydraulic efficiency and safety of the system in the context of possible breakdowns resulting from mechanical damage to the wall.
Surface heating, as the name implies, is heating using a surface. A very well-known example of surface heating is floor heating. Heat energy is accumulated in the concrete mass and subsequently transferred to the room as a result of natural radiation and non-forced convection. Unlike convection systems (heaters), it provides heat without air as the medium and acts similarly to the sun, a fireplace, a tiled stove or bonfire. This does not mean that the air is not heated; however, it is not used as the main heat medium. The system does not process the air; it does not dry the air and does not mix it with dust in an external device; etc.
Floor heating belongs to the family of surface heating systems, which means that it releases heat as a result of heat radiation. But nevertheless, the location of floor heating makes it a huge air convector. Warm air, heated from the floor, flows upward; for that reason floor heating increases movement of the air and, similarly to convection systems, mixes it with dust and allergens. The air is heated on permanent basis (it is gas and as such, it absorbs heat energy) as it may not stay resistant to the environment and its temperature changes.
In case of 3THERMO we may relate to 3 aspects:
- natural material: aluminium, contrary to PVC, is a natural element (aluminium, Al);
- an energy-saving product: each product improving energy efficiency presently belongs to ECO group. Less produced energy means less pollution to the environment.
- environmentally-friendly production: low-energy processes without technological sewage.
They are two different products applied for surface heating. In case of a concealed radiator, it is definitely easier to install aluminium mesh than a PVC mat under the plasterwork. An additional asset is provided in the form of 100% safety in case of damage (concealed radiators do not introduce water under plasterwork). The probability of scaling water systems is unquestionably lower, which with time may pose a problem for mats and a millimetre section of tubes.
However, capillary mats perform well as ceiling cooling systems. It is especially because the ceiling offers the greatest capacity in case of surface cooling involving absorption of heat energy. For this reason, a mixed system is worth considering, based on safe concealed radiators and capillary mats in ceilings as a cooling system.
Ceiling heating makes no sense because, contrary to floor heating, air ventilation zones are unnecessarily heated (chimney heat losses).
Concealed radiators are not a universal product. It is however worth noting that glazed buildings, even modern ones, have increased heat demand. This means that compensating for heat balance from surface heating (e.g. floor heating) may be difficult. On the other hand, combined floor-wall type systems stand a great chance of fully compensating for heat losses.
Concealed radiators will also perform well on external walls, for example by complementing the performance of trench convectors. Additionally, they offer a possibility of operating on one (high) parameter.
This is attributable to a number of reasons: the mass of concrete, resistance and the system location. For example, a room the capacity of 20 m sq. in case of 3THERMO means only 9 litres of water and 180 kg of concrete (plasterwork) mass. Floor heating for the same room capacity means about 78 litres of water and almost 3 tons of concrete (floor). This could be compared to driving a car versus navigating a ship.
Location of the heating system is also of importance. It is only wall heating that allows us to compensate for heat losses on ongoing basis, precisely as required and directly at the point of their occurrence.
Decreased inward resistance is also responsible for the speed of reaction, and 3THERMO is concealed under an average 3-mm layer of plasterwork. This is far less than any external floor cladding.