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PEX Tubing (PEX-A, B, C)

PEX is cross-linked polyethylene tubing for hot and cold water and radiant heating. This sheet explains PEX-A, PEX-B and PEX-C, the fitting systems that go with them and how to read the print line.

Ref PV-0009ASTM F876ASTM F877NSF 61

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

PEX tubing is polyethylene that has been cross-linked, which joins the polymer chains so the tubing resists heat, pressure and creep better than plain polyethylene. Tubing for water distribution is made to ASTM F876. ASTM F877 covers the complete tubing and fitting system. PEX for potable water is also certified to NSF/ANSI 61 for health effects. PEX is sized in copper tube size (CTS), so 1/2 in PEX has the same OD as 1/2 in copper tube.

How to identify

The print line shows the type (PEX-a, PEX-b or PEX-c), size, SDR, the ASTM standards, the fitting standards the tubing is approved for, NSF marks, pressure and temperature ratings, and a material designation code. Red, blue and white colors only help sort hot and cold lines. They do not change the tubing.

PEX types

Type	Cross-linking method	Traits	Common fitting systems
PEX-A	Peroxide method during extrusion	Most flexible; kinks can often be repaired with heat; holds expansion memory	Cold expansion with PEX ring (ASTM F1960), plus crimp and clamp per the maker
PEX-B	Silane method after extrusion, moisture cured	Stiffer; widely used and lower cost	Crimp or cinch clamp (ASTM F1807, F2159); some expansion systems with compression sleeve (ASTM F2080)
PEX-C	Electron beam (irradiation) after extrusion	Stiffer; kinks more easily	Crimp or cinch clamp

Fitting systems

Standard	System	How it works
ASTM F1807	Metal insert fittings with copper crimp ring or stainless clamp	Ring is crimped or clamped over the tube on the fitting
ASTM F2159	Plastic insert fittings with crimp ring or clamp	Same method, polymer fitting body
ASTM F1960	Cold expansion with PEX ring	Tube and ring are expanded, then shrink onto the fitting
ASTM F2080	Cold expansion with metal compression sleeve	Sleeve is pushed over expanded tube
Push-to-connect	Proprietary, listed to ASTM F877 or other standards	Fitting grips the tube with a collet and seals with an O-ring

Key points

Use only fittings the tubing print line lists. Expansion fittings on PEX-B or PEX-C are allowed only where both makers approve them.
Use the correct crimp tool and go/no-go gauge. Most crimp leaks are bad crimps.
PEX degrades in sunlight. Keep it covered in storage and follow the maker's UV exposure limit.
The material designation code on the print line covers chlorine resistance and other properties. Decode it with ASTM F876.
Pressure and temperature ratings are printed on the tubing. Use those, not general figures.

Common mistakes

Using F1960 expansion rings on tubing that is not rated for them.
Leaving PEX on a rack in direct sun.
Mixing crimp ring sizes.
Running PEX within the maker's minimum distance of a water heater or flue without a metal transition.

Governing standards: ASTM F876; ASTM F877; ASTM F1807, F1960, F2080 and F2159; NSF/ANSI 61; the local plumbing code.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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