When installing water circuits for underfloor heating, craftsmen usually use 2 types of pipelines - from metal-plastic and cross-linked polyethylene. The reasons for this choice are not clear to all homeowners, since the real range of materials is much wider: polypropylene (PP-R), copper, black steel, corrugated stainless steel. Our task is to consider these options and finally find out which pipe for a warm floor is better in terms of performance and price.
Evaluation Criteria for Pipe Materials
To choose the right pipes for a warm floor, you need to have a good understanding of the operating conditions of the material. Being inside the screed, the heating line not only transfers heat to the monolith, but also experiences mechanical stresses from water pressure and its own expansion.
Accordingly, strict requirements are put forward for the material:
- Underfloor heating (abbreviated as TP) is a low-temperature heating system where water is heated to a maximum of 55 degrees, the operating mode is approximately 40/30 ° С. To quickly transfer energy from the coolant to the concrete slab, the pipe walls must have sufficient thermal conductivity.
- The length of the TP loops often reaches 100-120 meters (depending on the chosen diameter of the pipeline). Longer length = high hydraulic resistance, exacerbated by the roughness of the inner surface. In simple language: the smoother the pipe walls, the easier it is for the pump to pump water along a long circuit and provide the required flow rate.
- Heating causes elongation of the warm floor pipes. Since there is nowhere to grow inside the concrete screed, one of two conditions must be met: a small coefficient of thermal expansion of the material or high elasticity and strength of the shell, allowing the pipe to fit in a limited space without breaking.
- Emergency: due to breakdown of the control valves on the mixing unit of the collector, the heating circuits are filled with boiler water heated to 70 ... 90 ° C. The material of monolithic pipes must withstand such temperature jumps without consequences.
- Other important points are corrosion resistance, protection against oxygen penetration, ease of installation and the absence of joints inside the monolith.
Note. For water circuits, laid "dry" method in wooden houses, less stringent requirements are put forward. TP are mounted without a coupler, there is plenty of room for thermal extension. Item 3 of the list is no longer relevant.
Not the least role is played by the cost of all TP components - pipelines, fittings, distribution comb. So we compare the materials used by the above criteria and price.
Characteristics of polymer pipes
The following types of plastic pipelines are used for transporting coolant in water heating systems of apartments and private houses:
- PP-R and PP-RCT - polypropylene random copolymer reinforced with a layer of aluminum, basalt or fiberglass. Modification of PP-RCT plastic is characterized by increased thermal resistance.
- PE-X - crosslinked polyethylene grades A, B and C. The products must have an oxygen barrier - a thin layer of impermeable polymer. For example, Rehau pipes use the complex compound ethylene vinyl glycol (EVOH).
- PE-RT - thermally stabilized polyethylene products with an oxygen barrier.
- PE-X / Al / PEX and PE-X / Al / PE are five-layer metal-plastic pipelines.
Reference. According to GOST 32415-2013, products made of polybutylene RV, polyvinyl chloride PVC-C, polypropylene block copolymer and homopolymer (PP-B, PP-N) are also suitable for the installation of heating networks.These materials are not widely used in private housing construction due to the worst technical parameters.
Briefly about how to connect pipe polymers in the process of assembling home heating:
- wiring from PP-R is joined by polypropylene fittings by soldering (thermal polyfusion welding);
- cross-linked and heat-stabilized polyethylene (PE-RT) is mounted axially in 3 stages - flaring the end, tensioning the fitting of the fitting, setting the sliding sleeve;
- metal-plastic is connected in 2 ways - compression or press.
Now we will give a brief description of each type of pipeline, go through the list of requirements and check how suitable the products are for water heating of floors in living rooms.
Polypropylene - material for radiator heating
Despite the price attractiveness and commitment of many craftsmen to use PP-R, we immediately note that it is impossible to make a warm floor from polypropylene pipes. It is not worth checking the approval in practice - just carefully study the technical characteristics of the material and read the reviews of homeowners who wanted to save money in this way.
How are pipelines made of polypropylene (see diagram):
- the inner layer of PP-R, forming the passage section of the highway;
- aluminum reinforcing foil that inhibits thermal elongation and prevents the penetration of oxygen;
- 2 adhesive layers fastening aluminum with polymer;
- the outer protective layer PP-R is white or gray (some manufacturers have green).
An important addition. Now polypropylene manufacturers instead of perforated foil lay a layer of basalt or glass fiber inside the pipe.
Let's see how the PP-R pipes are consistent with the requirements for floor heating branches:
- Thermal conductivity 0.24 W / (m • ° С) is the worst among polymer products. If we take into account the wall thickness of 3.4 mm at Ø20 mm (reinforced PP-R pipelines are not produced with a diameter of 16 mm), we obtain the heat transfer resistance R = 0.0034 / 0.24 = 0.014 m² • ° C / W. Resistance is too high for active heat transfer.
- There are no questions regarding the smoothness of the inner walls to polypropylene - a roughness of 0.01 mm does not create increased hydraulic resistance.
- When heated to 50 degrees, a 100-meter PP-R pipe with an aluminum layer will add 150 mm in length and 31 cm with fiberglass. The elasticity of polypropylene is very low, due to which the product inside the monolith will be under high load. The material may crack, primarily at the joints.
- Resistance to pressure and temperature is not in doubt. When the coolant is heated to 70 ° C, the PP-R line will calmly withstand a working head of up to 13 Bar. If you raise the temperature to 95 ° C, the pressure threshold drops to 9 bar.
- The polymer is resistant to any chemical influences and practically does not pass oxygen into the coolant. The main problem is the large number of joints falling under the screed, because it is unrealistic to bend the polypropylene section.
Note. The technical parameters of PP-R products are adopted according to the Valtec brand documentation published on the company's official website. We also took prices and characteristics of other pipe polymers from this manufacturer for fair comparison.
Explain some points. The value of the thermal resistance of the walls R = 0.014 m² • ° C / W will not tell the average user anything without comparison with the performance of other plastics. These calculations are given below in the descriptions of polyethylene and metal-plastic pipes.
The problem of heating polypropylene systems is the inability to visually check the quality of welding joints. Sometimes joints run a year after high pressure tests (crimping). Imagine the consequences of a leak inside a concrete monolith — searching for a defect, breaking the screed and repairing it.
A separate issue is a long fuss with installation, there will be many joints in concrete.Examples of heating circuits collected by house craftsmen from PP-R are shown above in the photo. Even the low price of the pipe Ø20 - 51 ... 83 rubles. (0.8 ... 1.25 cu) per linear meter - is not the basis for the use of such pipes in warm floors.
Parameters of crosslinked and heat-resistant polyethylene
Pipes made of plastic PE-X are produced in two varieties - 3 and 5-layer. The difference lies in the location of the anti-diffusion barrier - in the first case, the impermeable EVOH polymer serves as the outer shell of the pipe, in the second - it is laid inside the wall and glued to both sides of the polyethylene. External color - brown, silver, red.
Users often ask themselves which polyethylene pipes it is better to take for floor heating - PE-X or PE-RT, how do they differ. We answer:
- the molecular lattice of PE-X plastic is crosslinked in 3 ways, hence the three types of polyethylene - A, B and C;
- from the point of view of installation and operation of heating, pipes from PE-X / A do not differ from PE-X types B and C;
- material of increased heat resistance PE-RT is made from ordinary polyethylene using cheaper technology - a complex polymer molecule is modified using branches;
- PE-RT is inferior to PE-X in terms of durability, strength and thermal stability;
- PEX is significantly more expensive than PE-RT, about 20–40%;
- PERT pipe walls are devoid of an anti-diffusion barrier; therefore, the coolant is saturated with oxygen at a rate of at least 0.1 g / m³ • day. (on open air);
- PE-RT material is thermoplastic, the pipeline can be repeatedly melted and welded without loss of properties.
Reference. The cost of a Valtec 16 x 2 mm cross-linked polyethylene pipe is 51 rubles. per meter (about 0.8 cu). A product of the same diameter made of thermostable PE-RT plastic costs 33 rubles / 1 m. (0.5 cu).
Let's move on to our list of requirements:
- Pipe for a warm water floor “PEX” and “PERT” has the same thermal conductivity - 0.38 W / (m • ° С). We calculate the thermal resistance of the walls with a thickness of 2 mm: R = 0.002 / 0.38 ≈ 0.005 m² • ° C / W - almost 3 times lower than that of the SPR. That is, polyethylene circuits much better transfer heat to the screed.
- Equivalent surface roughness - 0.007 mm - an excellent indicator of pipe smoothness.
- Having warmed up at 50 ° C, the 100-meter free section of the PEX pipeline will be extended by as much as 100 cm. But thanks to the elasticity and some mounting techniques, the expansion inside the concrete slab is quietly compensated by the material.
- The maximum working temperature of the PE-X material is 90 ° C, PE-RT is 80 degrees, the short-term allowable is 95 and 90 ° C, respectively. The operating pressure of the coolant is 6 ... 10 Bar, depending on the degree of heating. The parameters satisfy the requirements for heating water circuits.
The weak point of polyethylene systems is oxygen permeability. Equipped with a PEX barrier, it allows less than 0.1 g / m³ per day, while PERT allows much more. But since the pipes are monolithic with cement-sand mortar, air access is significantly limited, oxygen penetration is minimized.
Polyethylenes have a twofold property - molecular memory, which causes the pipeline to bend to the original shape of the bay. The feature complicates the fastening of heating loops to the floor insulation - if the pipe is not rotated around its own axis, the ends will begin to bulge upward. How to deal with the described phenomenon, look at the video of our expert.
The positive effect of molecular memory is the ability to recover from a break. It is enough to straighten the place of damage and heat it with a building hair dryer - plastic will take its previous shape without losing elasticity and strength.
We analyze the properties of metal
In fact, this five-layer pipe is an analogue of the PEX material, where a rigid aluminum frame with a thickness of 0.25 ... 0.4 mm (depending on the diameter of the product) acts as an EVOH antioxidant polymer. Inside, a self-supporting tube made of cross-linked polyethylene passes, on the outside - a shell of the same plastic.Layers of construction are fastened with special glue.
Reference. Marking of metal-polymer pipes corresponds to the structure - PEX-AL-PEX. An interesting point: the Rehau brand offers a universal line of RAUTITAN Stabi pipelines with an outer shell of ordinary (not cross-linked) polyethylene.
We will analyze metal-plastic according to initially specified criteria:
- The thermal conductivity of the five-layer structure is 0.45 W / (m • ° С), the wall thickness of pipes with a diameter of 16 and 20 mm is 2 mm. Therefore, the resistance to heat transfer R is equal to 0.002 / 0.45 = 0.004 m² • ° С / W.
- The extension from heating of a 100-meter section by 50 ° C is only 13 cm.
- Operating temperature at a pressure of 10 Bar - up to 95 degrees, short-term emergency - 130 ° C. The oxygen permeability of the walls is close to zero.
- The price of the Valtec Ø16 x 2 pipe is 60 rubles. (0.9 cu), Ø20 x 2 - 97 rubles. (1.45 cu) per linear meter.
Please note: thermal conductivity, operating temperature and elongation of metal-plastic structures are the best among all polymer pipes. The smoothness of the material is not mentioned, since the roughness value is identical to polyethylene - 0.007 mm.
An important difference between metal plastic is the absence of molecular memory. When bending, the rigid aluminum frame takes the required shape, overcoming the elastic strength of the polyethylene layers. The specified property is a great help during installation, the main thing is to maintain a minimum bending radius of 6 and 8 cm for pipes Ø16 and 20 mm, respectively.
Metal pipes for floor heating
In modern heat supply networks of country houses, steel, stainless and copper pipes are used. For installation of floor water systems, 2 types of metal pipelines are used:
- annealed copper with an outer diameter of 15, 18 and 22 mm with a wall thickness of 1 mm (sold in bays of 25 m);
- corrugated stainless annealed ½ and ¾ inches (Ø15 ... 20 mm), bay meter - from 10 to 50 m.
History reference. In Soviet times, warm floors were arranged in kindergartens in accordance with the requirements of building codes. Heating circuits were welded from water-gas galvanized pipes made of black steel.
Let us evaluate the parameters of metal pipes according to the criteria:
- The thermal conductivity coefficient of copper and steel is so great (389 and 45 W / m • ° С, respectively) that it makes no sense to make calculations - according to this characteristic, the metal will plug any plastic into the belt.
- The equivalent roughness of new products is 0.01 mm. During operation, the smoothness of the walls deteriorates, the hydraulic resistance gradually increases.
- The linear expansion of metals is insignificant in comparison with polymers - 55 ... 85 mm per 100 meters of the heat main at a temperature delta of 50 ° C. The materials are flexible enough to lengthen inside the concrete and not break the screed.
- Copper Ø18 x 1.0 mm quietly holds a working pressure of up to 67 Bar at a maximum temperature of 200 ° C. Corrugated stainless steel parameters are 15 Bar and 150 degrees, respectively. The stated indicators cover the requirements for TP with a large margin.
- Steel and copper do not allow oxygen to pass through, but they are subject to slow corrosion. Weaknesses - sections crossing home electrical wiring lines.
The problem with a flexible stainless pipe is a corrugated corrugated structure that creates significant hydraulic resistance to fluid flow. At a length of 1 cm there are at least 20 peaks more than a millimeter high. The second moment: in the troughs small sand will begin to gather, traveling along the system along with the coolant.
Information on the price of materials. A copper pipe Ø18 x 1.0 costs about 500 rubles. per meter (7.5 cu), stainless steel Ø20 mm (internal - 15 mm) will cost 155 rubles / 1 m (2.3 cu).
Despite the excellent performance, copper is rarely used for the installation of TP. Causes:
- the material is several times more expensive than polymers;
- the complexity of laying the pipe - for accurate bending and forming loops of the warm floor, experience is required;
- the pipeline is afraid of kinks that can only be fixed with professional soldering.
Regarding corrugation: besides problems with hydraulics, there is a question of mistrust. The fact is that the material appeared on the market relatively recently and did not manage to work out in floor systems for 10-20 years. That is, the real durability of the stainless steel is unknown.
Choosing the best option for TP
If we carefully study the analysis of each type of pipelines, we can draw a preliminary conclusion: copper wins in all operational indicators, but significantly loses to polymers in price. Stainless steel corrugation will also not be an alternative to polyethylene - it is twice as expensive and worse in hydraulics.
What pipe to use for a warm floor in the first place:
- Number 1 of our rating is PEX-AL-PEX, a metalwork proven by many years of practice. The material is relatively inexpensive, convenient for DIY installation, durable, transfers heat well and lengthens slightly from heating.
- Cross-linked PE-X polyethylene - pipes for professionals who can make high-quality contours of TP. "PEX" is easily restored after a break, but conducts heat worse and expands greatly from rising temperatures.
- Heat-resistant PE-RT polyethylene is a budget option for professional installation. The main disadvantages are oxygen permeability and a significant reduction in service life in case of overheating.
- The fourth place of the copper pipe is due to the high price that is not available to most ordinary homeowners. If this factor is not taken into account, copper will be an ideal option for underfloor heating.
- Corrugated stainless steel is good for short sections, for example, connecting hoses and hoses. Laying corrugated pipes under the screed is not a very good solution.
- Polypropylene is not used at all.
Comment. When comparing different piping systems, the cost of fittings was not taken into account, since floor circuits are mounted without connections.
Recommendation for the proper installation and concreting of PE-X and PE-RT pipelines. To reduce the elongation of heating threads, do not exceed the number of pipes in one circuit - 100 m, ideally 80 m. Before filling the solution, fill the system with water and pump up the test pressure (1.5 times higher than the working one). The technology for installing TP is described in detail in a separate article.
We add a few arguments in favor of choosing polyethylene or metal plastic for heating floors. Firstly, polymers have long and successfully been used in European countries. Secondly, the chemical composition of the basic substance is continuously improved, and the properties are improved. Thirdly, polymer pipes are very durable, the standard service life is 50 years.
About the diameter of heating pipes
Usually, with the self-arrangement of water underfloor heating, homeowners have the question of which pipe diameter to choose - 16 or 20 mm. We will try to answer in an accessible language:
- in the vast majority of cases, heating threads are laid with pipes Ø16 mm (inner passage - DN10);
- diameter of 20 mm (DN15) must be used on long contours, whose length is 100 ... 120 meters;
- the use of larger pipelines is justified in rooms of a large area with high ceilings, heated only by the TP system without the help of radiators.
The best way to choose the right diameter, and at the same time find out the consumption of pipes for underfloor heating, is to calculate. We invite you to familiarize yourself with the calculation methodology published as a detailed guide.