Warm water floors have long proven their worth. They are boldly used as the main source of heat, and they cope with the task. However, when designing, the question remains, which pipes to choose for a warm floor.
There are several options:
However, first you need to understand what the requirements are for pipes for underfloor heating, and what the operating conditions will be. As a result, you can shorten the list of materials and come to one or two optimal options, of which it will remain to choose the most affordable.
Natural requirements are durability and reliability. However, under these words, the qualitative characteristics of pipes should be considered without such a rough generalization..
Requirements for pipes for underfloor heating
In the underfloor heating system, by default, pipes are laid over the entire area of the heated room and filled with a screed. The screed is needed to evenly distribute heat and accumulate it. Already secondarily to provide strength for the installation of flooring.
The connection to the boiler is carried out through the manifold group. A special branch pipe with a sufficient number of outlets for direct supply of warm water and return is separately called a collector or a comb. The collector group is installed at one point per floor, less often it is divided into several separate groups. All settings and adjustments, as well as monitoring the operation of the heating system, take place precisely on the collector group. Additionally, the heating boiler itself controls the maximum temperature of the coolant in the system.
About temperature. For underfloor heating, the maximum permissible surface temperature in living quarters is +28 ° C. For non-residential areas, the value is slightly higher than +31 ° С. All the same, compared to radiator heat supply, where the coolant can be heated up to +95 ° C, warm floors are barely warm, although this is enough for heating. An important disclaimer, it is the temperature of the floor surface that is regulated, and not the coolant. In the event of a strong cold snap or significant heat loss, the temperature of the coolant for heating the house is needed up to +36 ° C, higher is simply impractical.
The pipes are laid evenly over the entire floor. To avoid less heating where the ending lies, because the water has already lost some of the heat at the very beginning, the pipe is laid in a coil or in a spiral to the center with a double step between the loops and then back along the same route. It turns out that at each point the floor heats up both from the direct flow of water and from the reverse.
Knowing all these nuances, you can voice the requirements for pipes for a warm floor:
- Lack of connections inside the screed.
- Corrosion resistant.
- Sediments should not accumulate on the walls, there should be no silting.
- Flexibility – pipes must bend easily and follow difficult routes.
The basis is thermoplastic, extrusive polyethylene, reinforced with a reinforcing layer. Aluminum foil or metal mesh is used as reinforcement. The main advantages of metal-polymer pipes:
- Flexibility, retain its shape after deformation.
- It is easy enough to keep the inner diameter when bending.
- Tensile strength and moderate linear expansion restrained by the reinforcement layer.
- No oxygen diffusion.
- Delivery in bays of 200 meters.
The latter point is often presented as the main benefit. After all, it is the large length of metal-polymer pipes that allows you to lay long heating circuits of a warm floor without using connectors and couplings. However, no less important is the perfectly smooth surface of the inner walls and the absence of oxygen diffusion. Given the rather low temperature of the coolant in the presence of oxygen, the development of various anaerobic bacteria is possible and, as a result, siltation.
Polypropylene has earned trust both in cold and hot water supply systems and in heating. Reinforced polypropylene pipes can withstand pressure up to 25–35 bar and coolant temperature up to +95 ° С. However, these advantages are not relevant for floor heating systems..
The second important point is the excessively thick walls of 2.5–3 mm, which also does not make it attractive, because for pouring into a screed it is desirable to have as small an outer diameter as possible.
The material is characterized by high oxygen diffusion, approximately 900 mg / m2·day. Considering the water temperature of +28 ° C, ideal conditions are created for the development of aerobic bacteria. In the course of their life, the walls are silted up until the canal is completely blocked..
And the final verdict “unusable” deserve such pipes for a maximum length of 6–12 meters, without the ability to bend them freely for laying. Fittings and solder joints are required. The latter, although they are distinguished by increased strength, even more than press fittings of metal-plastic, it all depends on the quality of the installation. It is impossible to rely entirely on the fact that the joints will not leak over time, and they should not be poured with concrete either..
Crosslinked polyethylene pipes are in many ways similar to metal-polymer pipes, in the absence of only a reinforcing layer. They themselves are quite strong due to the crosslinking of the polymer at the molecular level. The permissible temperature is up to +45 … + 60 ° С, which fits into the requirements for a warm floor, and a completely smooth inner surface with a minimum roughness value, which helps to reduce the hydraulic resistance and reduces the risk of pipe siltation.
Pipes are manufactured and delivered in coils up to 150-250 meters long, so that it is possible to lay contours even over large areas without unnecessary connections.
The disadvantage of XLPE is its high coefficient of thermal expansion. At a coolant temperature of +28 ° C, this still affects, albeit weakly. This feature is compensated by the flexibility and elasticity of the pipe, the high compressive limit.
Oxygen diffusion is slightly lower than that of polypropylene – 650 mg / m2Day, and still too high.
In fact, none of the options specified the thermal conductivity of the material. Indeed, in polymers it is not high, and logically steel pipes, although they are subject to corrosion, still give off heat much more actively. Only in the underfloor heating system, the rate of heat transfer is not so important. The uniformity of floor heating is important, so that even high thermal resistance plays into the hands of polymer materials.
We can say for sure that polypropylene is not suitable. There is no way to get rid of a large number of fittings and connections, and polypropylene itself allows oxygen to pass through, which contributes to silting.
The best option is only metal-plastic pipes that can bend easily, do not allow oxygen to pass through, and have a large length.
XLPE is a reasonable alternative, but only when using a pipe with an additional barrier layer to eliminate oxygen diffusion.