< back

Which pipes to choose for the installation?

Running water in the house and central heating are standard today. Every investor must decide sooner or later which material to choose for the installation. Just a dozen or so years ago, the primary material for installations was steel pipes. Currently, they are used less and less: they have been replaced by pipes made of materials such as copper and plastics. They are more resistant to corrosion and do not scale up. It is also significant that installations made of them are much simpler and faster to build.

For the construction of cold and hot water installations, as well as for central heating installations, three basic groups of materials are used:

In each of these groups, there are different varieties of pipes, for example, steel pipes: black, galvanized; copper pipes: hard, semi-hard, or soft; and pipes made of various types of plastics.

Sometimes it is worth thinking longer, comparing several products, and considering all advantages and disadvantages, ease of installation, post-warranty service, and many important factors that are often ignored when making a purchase decision. It may turn out that cheap solutions do not meet our expectations at all.

STEEL

Until recently, the primary material for water installations in our country was steel, which has very high mechanical strength. This eliminates, among other things, the need for dense placement of pipe fixing points. An unquestionable advantage of steel is its resistance to high temperatures and the fact that it has relatively low thermal expansion. However, it is heavy and prone to corrosion. It conducts heat well, so water in such pipes cools down quickly. It is elastic and transmits sounds well. It has a rough surface, which promotes the deposition of scale and rapid reduction of the internal cross-section of the pipes ("clogging" of the installation). Elements of steel installations are connected by thread or welding. For heating installations, pipes made of "black" steel, unprotected against corrosion, are used. They can be connected by welding and bent hot, which greatly simplifies installation work. However, welding steel requires a very high temperature, which can only be achieved with special oxy-acetylene torches. Welding also avoids some fittings, which would otherwise increase flow resistance. This is of particular importance in traditional gravity-flow central heating installations. This steel is not suitable for tap water due to its susceptibility to corrosion. For tap water installations, only galvanized pipes are suitable ("white" steel). These, in turn, cannot be used for heating installations, because at temperatures above 60°C, the zinc layer loses its protective properties. Galvanized steel pipes must not be welded or hot-bent. Therefore, the consumption of fittings is high, labor input is significant, and flow resistance is greater. Today, in single-family housing, steel is falling out of use. Although the material itself is several dozen percent cheaper than modern alternatives, the weight and difficulties of processing make labor almost one and a half times more expensive than in the case of other materials. What is worse, steel is not very durable. The durability of a steel installation is primarily affected by the quality of the transported water. Steel pipes are susceptible to corrosion caused by oxygen, carbon dioxide, and dissolved mineral compounds contained in the water. Calcium and magnesium ions settle very easily on the rough, non-smooth walls of steel pipes, forming boiler scale. Failures caused by corrosion can occur after just a few years, and complete replacement has sometimes been necessary after ten years.

COPPER

Undoubtedly, copper is a better material for water installations than steel. Copper is resistant to temperature, pressure, and ultraviolet radiation. It does not age. Pipes made of it offer negligible hydraulic resistance, so they can have a small diameter; this saves material and space, and the installation is easily placed under plaster, which is why they work well, for example, as branch pipes from cold and hot water risers. Unlike some plastics, there is no oxygen diffusion, which is very important for central heating installations. Installation is simple and fast, and the workspace is small. A copper installation does not scale up. Very important: copper inhibits the growth of bacteria (including the very dangerous Legionella) and algae, which most often occur in plastic pipes. The price of the material is 40% higher than steel, but the labor cost is 30% lower, and the lifespan is at least four times longer (50 to 100 years!). Copper pipes are not very resistant to scratching. Therefore, the copper installation must be well protected against small solid particles, such as sand, mortar, and rust particles. A mesh filter with a mesh size of no more than 80µm (0.08 mm) should be installed at its inlet. Although copper pipes are resistant to hot and cold water, they can corrode if the water is soft and contains large amounts of aggressive carbon dioxide. In Poland, restrictions on copper installations mainly apply to mountainous areas, where water is usually soft. Corrosion can also be caused by incorporating, for example, faucets or devices made of galvanized steel or aluminum into a copper installation. Copper pipes are produced in three varieties: hard, semi-hard, and soft. - Soft pipes can be profiled without much trouble, which significantly reduces the number of connections and shortens the installation time. These pipes are used mainly for long installation sections laid under the floor (underfloor heating), connecting radiators, or for water installations run in the screed. They are the least resistant to mechanical damage and should not be joined using compression fittings. - Semi-hard pipes are more resistant to mechanical damage than soft ones, but they can be easily bent using benders or internal springs, provided they are of the appropriate size. - Hard pipes, available in sections up to 6 m, cannot be bent. Every change in pipe direction requires the use of an appropriate fitting, which is joined to the pipe by soldering or clamping. They are the most mechanically durable, which is why they are used in sections of central heating, cold, and hot utility water installations exposed to damage, run in chases or directly on the wall. Hard copper pipes are perfect for piping within the boiler room. They are also often used to modernize old installations, where they replace old steel pipes. The set of connectors is very extensive. Curves are characteristic of this material. For example, in addition to standard elbows, sweeps are made with a gentler transition between the arms, so the water flow breaks less abruptly. The basic way to join copper elements is soldering. At some points in the installation, mainly when connecting to end devices or to installations made of other materials (steel or plastic), threaded connections are also used. Another type of connectors – compression fittings – are very easy to use even for amateurs. In the case of a small system where higher cost is not significant, we can use them throughout the installation.

PLASTICS

Currently, plastic water installations are gaining more and more popularity. Plastic pipes do not corrode, and boiler scale does not form. Plastic pipes do not transmit vibrations and dampen noise generated in the installation. They are chemically inert, so they do not react with water and its compounds. They also do not affect the taste, color, or smell of water. Plastic pipes are lightweight, easy to transport, and can be installed by yourself. Making connections is relatively easy and takes very little time, though it sometimes requires fairly expensive welding or clamping machines.
The main disadvantage of plastic pipes is the penetration of oxygen through their walls. The higher the temperature of the working medium in the pipe, the more oxygen penetrates. This does not affect the durability of the pipe itself, but oxygen in the installation water is detrimental to all metal components and devices (e.g., radiators) present in the system.
Unlike rigid steel pipes, they require better fastening to the walls because they can deform under high temperature in the hot water system. They also have very high longitudinal deformability, which is why they require compensation on longer sections. Unlike copper pipes, they have very thick walls, so they require very deep chases to be placed under plaster. A very important factor is that most plastics (except polybutylene) protect much worse than copper and steel against the development of bacterial flora in pipes, especially against the very dangerous Legionella bacteria.

Types of plastics from which pipes are made:

- PVC (polyvinyl chloride) and CPVC (chlorinated polyvinyl chloride),
- PE (polyethylene: PE-LD soft and PE-HD hard),
- PE-X (cross-linked polyethylene),
- PP (polypropylene),
- PB (polybutylene),
- Multilayer pipes (combined various plastics and interlayers, e.g., aluminum foil).

PVC (polyvinyl chloride) and CPVC (chlorinated polyvinyl chloride).

This is the oldest of all plastics used for installations.
PVC has very limited application. The low temperature range (0 - 50°C) in which it retains its properties makes this material suitable only for cold water installations. At sub-zero temperatures, PVC is brittle and is not resistant to tension and bending. CPVC has better properties and can be used not only for hot water but also for central heating (temperature range 0 - 100°C), though the embrittlement temperature is still 0°C. CPVC can also be used for cold water, but it is more expensive than PVC.
Pipes made of it are delivered only in straight sections. The rules for running them do not differ much from those for steel installations. At higher temperatures, the mechanical strength of PVC decreases significantly. It begins to soften slightly below 80°C, but 60°C is considered a safe temperature.
The basic method of joining PVC elements is solvent welding (gluing). At some points, PVC must be connected to metal (boiler outlet, faucets, etc.). Threaded connections are used in such places. The fittings are factory-prepared. The presence of threaded connections reduces the pressure resistance of the installation.
Installations made of PVC and its varieties are very easy to build yourself, of course, according to a design prepared by a qualified specialist. No specialized tools are needed for the work; a hacksaw, a sharp knife, and a screwdriver are enough.

PE polyethylene.

Another plastic used in water installations is PE. It comes in many varieties.
The two most popular are:

- "soft" type, denoted as LDPE or PE-LD (Low Density Polyethylene), designed for low-pressure installations,
- "hard" type, HDPE or PE-HD (High Density Polyethylene) for high-pressure installations.

Both are characterized by high chemical resistance, low specific weight, and high smoothness of the pipe walls. They can only be used for cold water installations; at temperatures above 20°C, their strength drops sharply.
There is also medium-density polyethylene with increased thermal stability designated as PE-RT. Cross-linked high-density polyethylene, PEX, has much higher resistance – up to +95°C in continuous operation, allowing the pipes to be used for both types of water and heating installations.
All polyethylene pipes are flexible and ductile, so they can be bent sharply, which also saves on fittings, mainly elbows. An important advantage of polyethylene is the low embrittlement temperature: -25°C. Thus, there are practically no contraindications to using it outdoors in installations exposed to freezing. Welding and compression fittings can be used for connection.

PE-X cross-linked polyethylene

This is polyethylene subjected to special processing (cross-linking, i.e., introducing cross-links between polymer chains), available in several varieties with slightly differing properties.
It is flexible and resistant to damage caused by stress. The pipes feature shape memory. It is also characterized by resistance to metal ions and UV rays. The operating temperature from -10 to 95°C allows for cold, hot water, and heating installations.
It is a durable material (installation lifespan of over 50 years), there is no corrosion or clogging of pipes with deposits, the pipes are lightweight and flexible, making them easy to lay, and they are also resistant to accidental mechanical damage. An installation made of PE-X dampens sounds and does not transmit vibrations.
Cross-linked polyethylene is particularly recommended as a material for drinking water pipes because it is non-toxic, free of heavy metal ions, and microbiologically resistant. Compression fittings (threaded or press-fit) are used for connections. Pipes made of cross-linked polyethylene are most often produced as multilayer PE-X/AL/PE-X pipes with an oxygen barrier (anti-diffusion layer), which limits the penetration of oxygen into their interior.

PP polypropylene

In water installation technology, PP polypropylene has found wide application, specifically one of its varieties designated as PP-R or PP type 3, PP-3 for short.
Ordinary and "heat-stabilized" PP pipes are produced. The former are used in cold water installations, and the latter for central heating and hot water installations. This is because although polypropylene withstands high temperatures (even above +95°C), it also has a high coefficient of linear thermal expansion. This property must be taken into account when designing and building polypropylene installations. In "heat-stabilized" pipes, thermal expansion drops up to six times.
There are also PP pipes with an anti-diffusion coating, which prevents oxygen from penetrating inside (this unfavorable phenomenon accelerates the corrosion of steel parts of the installation, e.g., radiators).
PP pipes are quite rigid, so any changes in direction require the use of fittings. They are joined to pipes by socket fusion welding. In addition, unions, threaded ends, and special connection blocks are used.
Polypropylene pipes are highly resistant to low temperatures (from -40°C) and are usually installed on the surface. They can be exposed, hidden in installation ducts, or behind protective screens. If run in chases, the chases must not be filled with mortar, as this would prevent free movement of the pipes under the influence of temperature changes.
Ultraviolet radiation adversely affects polypropylene products; therefore, pipes exposed to UV radiation should be shielded or protected by painting with a protective coating. Polypropylene accumulates static electricity on its surface and should not be used to transport flammable and explosive substances.

PB polybutylene

The newest of all "installation" plastics is polybutylene.
It is highly flexible and – which is rare among plastics – has no shape memory (the pipe does not spring back after being unrolled). It is characterized by flexibility (saving on fittings), impact strength (does not crack upon impact), high resistance to creep (slow deformation under long-term load), wear, stress cracking, and aging. Products made of it are easy to transport and install – pipes can be bent and run like electrical cable.
The embrittlement temperature is -25°C. Above this, freezing water does not harm the pipe. If an ice plug forms, the pipe simply expands with it, and after thawing, it returns to its original shape. It is also exceptionally resistant to high temperatures up to 90°C, making it suitable for all types of water installations.
An important feature of PB is its ability to inhibit bacterial growth. In this respect, it is close to copper, which exerts the strongest bacteriostatic effect among metallic materials. One hears of manufacturers who, for this reason, coat the inner surfaces of steel pipes with a thin layer of PB.
Installation involves cutting the appropriate section of pipe from the coil and pushing it into the appropriate fitting – brass compression or threaded. Polybutylene pipes can also be joined by welding, which, however, requires appropriate equipment. Although the material itself is the most expensive among the plastics used in water installations, the ease of installation and operational advantages make its water installations highly cost-competitive.

Multilayer pipes

This solution allows combining the best properties of metals and plastics. The pipes consist of three layers: inner and outer made of polyethylene (PE-HD, cross-linked PE-X, or polypropylene) and a middle interlayer made of foil – usually aluminum. Aluminum prevents oxygen from penetrating the pipe, significantly reduces its thermal expansion, and eliminates shape memory; the pipe can be permanently shaped as needed. The introduction of a metal insert also increases the thermal resistance of pipes – some withstand short-term exposure to 110°C. Therefore, multilayer pipes are primarily used in heating installations. The plastic provides chemical resistance, smoothness of the external surface, thermal insulation, and dampens installation noise. The metal, on the other hand, prevents oxygen penetration, reduces thermal expansion, eliminates shape memory, and increases temperature resistance. These characteristics mean that multilayer pipes are used primarily in heating installations.
On the other hand, insulated multilayer pipes protect cold water installations from condensation and hot water from heat loss. Their additional advantage is good noise dampening. The inner surface of plastic pipes is up to several hundred times smoother than steel pipes. This greatly reduces flow resistance, and deposits do not form on the walls. Plastics are chemically inert, so they do not react with water or its compounds. This is a great advantage. However, there are also disadvantages. Most plastics (except polybutylene) protect pipes from the development of bacterial flora much worse than copper and steel.
Depending on the type of plastic, pipes are sold in coils or straight sections. Those in coils are flexible, so they can be used in underfloor heating systems, where they must be bent and should not be joined along their length.
The inscription on the side of the pipe indicates which materials make up the pipe. It lists the materials of subsequent layers, e.g.:

PEX/Al/PEX (cross-linked polyethylene / aluminum / cross-linked polyethylene),
PP-R/Al/PP (polypropylene type 3 / aluminum / polypropylene),
PEX/Al/HDPE (cross-linked polyethylene / aluminum / high-density polyethylene).

The basic method of joining multilayer pipes is using compression or press fittings. In the case of PP with an aluminum interlayer, welding can also be used after removing the Al layer at the pipe ends with a special shaver.

Coefficients of thermal expansion of plastics
plastic:                 multilayer pipes    PVC and CPVC      PB      PE      PP     PEX
coefficient of expansion:       0.03 - 0.05                0.08             0.13   0.14   0.15   0.18

Pay attention to the minimum allowable bending radius of specific pipes. Excessive bending causes the material to crack. Plastic pipes do not transmit vibrations and dampen noise. The durability of the installation depends on the temperature and pressure of the water. Too high a temperature accelerates the aging process of the material. The most resistant are: polypropylene, polybutylene (up to 90°C), PE-X, and multilayer pipes (up to 95°C). Cold water installations therefore last the longest, but here too clear differences appear – PVC pipes are the least resistant to low temperatures (down to 0°C), while polypropylene is the most resistant (down to -40°C).

The main disadvantage of "plastic" pipes is the ease with which oxygen penetrates their walls (the higher the temperature of the working medium in the pipe, the more oxygen penetrates). Although this does not affect the durability of the pipes themselves, oxygen in the water adversely affects all metal components and devices in the installation (promotes corrosion).

For this reason, pipes with an anti-diffusion coating (limiting the penetration of oxygen into their interior) or with a metal insert, which completely seals the pipe and limits dimensional changes under the influence of changing temperatures, are more suitable for **central heating installations** and domestic hot water.

< back