What diameter and type of threads for PE pipes do I need
The connection between a polyethylene pipe and a metal fitting is a critical point in the entire heating system, where two materials with different physical properties meet. Choosing the correct diameter and thread type is not only a matter of compatibility, but primarily a guarantee of long-term sealing and operational safety.
Key dimensions and markings of PE pipes
When selecting a fitting, you must base your choice on the outer diameter of the polyethylene pipe, not on the inner or nominal diameter as with steel pipes. Common differences in pipe wall thickness mean that a pipe marked as DN20 may have an outer diameter of 25 mm, while another manufacturer offers a variant with an outer diameter of 26.6 mm, which requires an accurate measuring tool.
- The outer diameter (OD) is decisive for the selection of a crimping or compression nut.
- PE pipe markings are often given in millimeters (e.g., 16x2.0 mm), meaning 16 mm inner diameter and 2 mm wall thickness.
- For heating systems, pipes with outer diameters of 16, 20, 25, 32, and 40 mm are most commonly used.
Difference between metric and pipe thread
The most common mistake during installation is confusing the metric thread system (M) with the standard pipe thread (G), which may look similar at first glance but have different pitch and profile. Brass fittings intended for polyethylene pipes almost exclusively use a metric thread on the metal connection side, while the part for the pipe itself is threadless and serves to secure the nut.
For common domestic applications and floor heating, combinations such as M12, M14, M16 up to M24 are used, with these dimensions corresponding to the outer diameter of the pipe plus additional space for the sealing ring. Using an incorrect threading tool may damage the threads in the brass body or result in insufficient tightening, leading to water leakage.
Types of fastening: Compression versus Crimping
The choice between compression and crimping systems depends not only on the availability of tools, but also on future maintenance requirements and the type of installation. Compression fittings use the force of a tightened nut to compress the sealing ring against the pipe wall, allowing for disassembly and reuse if necessary.
Crimping systems, on the other hand, use the mechanical force of a crimper to create a permanent deformed connection, which is more resistant to vibrations and thermal expansion, but is not reversible for repairs. For common installations in apartments and family homes, compression solutions are often recommended due to their flexibility, while crimping is a better choice for industrial piping.
- Compression fittings allow for simple inspection and repair without special tools.
- Crimping fittings provide higher mechanical strength and are more resistant to thermal shocks.
- For PE pipes, it is important to use a crimping nut with a stainless steel ring for increased corrosion resistance.
Influence of the nut and sealing material
The material of the nut and sealing element has a decisive impact on the longevity of the entire connection, as polyethylene is a plastic material that behaves differently from metal. Using cheap steel nuts without surface treatment can lead to rapid corrosion, which weakens the grip and causes leakage, especially if the connection is exposed to moisture or chemicals.
For professional applications, the standard is to use brass nuts with a nickel coating or even fully stainless steel nuts, which ensure long-term stability. Sealing rings must be made of a material resistant to heat and water, with high-quality NBR or EPDM rubber rings being the ideal choice for heating systems.
Practical examples from installation practice
Based on experience from thousands of installations, we can state that the most common cause of leaks is not poor design, but an inaccurate pipe cut or incorrect choice of fitting size. For example, if you cut a 20 mm pipe and use a fitting intended for 25 mm, the sealing ring will not be properly compressed and water will leak around the connection, leading to plaster damage.
It is also important to ensure the cut is clean, with no sharp edges that could damage the sealing ring during installation. In practice, we have recorded cases where a customer used an old fitting with a damaged thread, which made it impossible to achieve the correct tightening torque and resulted in a leak. Therefore, always check the condition of the threads before installation.
- Always use fresh and undamaged sealing rings for each new installation.
- Cuts must be perfectly perpendicular to the pipe axis, otherwise uneven compression will occur.
- Tightening the nut must be done according to the instructions, without excessive force that could damage the plastic.
Visual inspection of the sealing ring
A high-quality sealing ring must have a smooth, flawless cut and must not be deformed or dried out, as even a microscopic crack will cause a pressure leak.
Frequently asked questions
How to determine the correct diameter for my PE pipe?
You must measure the outer diameter of the pipe using a caliper and compare it with the manufacturer's table, remembering to subtract the wall thickness.
Can I use a universal coupling for different cross-sections?
Universal couplings do exist, but their tightness is not always guaranteed, and it is recommended to use specific parts for a given diameter for maximum safety.
How long will a PE pipe connection last?
A properly installed connection with quality materials should last the entire service life of the heating system, which is usually 20 to 30 years.
Choosing the correct diameter and type of thread is the basis for a functional and safe heating system that will not trouble you even after years of operation. Thorough preparation, accurate measurement, and following technical procedures will save you a lot of problems and repair costs.
Do you have a question about this topic?
Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.