Neither is better as a category. PEX-A and PEX-B name the process used to crosslink the polyethylene: peroxide for PEX-A, silane for PEX-B (electron beam is PEX-C). The Plastics Pipe Institute (PPI) says tubing made by any approved method “must meet the same qualification and performance requirements” in ASTM F876, AWWA C904 and CSA B137.5, and that “the letter designations are not related to any type of rating system.”

What does differ, and what decides a repair, is printed on the pipe itself.

How the three types are made

Type Crosslinking method (PPI)
PEX-A Organic peroxides crosslink the polyethylene as it is extruded
PEX-B A silane molecule is grafted on, and the pipe crosslinks after extrusion with moisture and heat, such as steam curing
PEX-C Extruded pipe is exposed to a dose of high-energy electrons

PPI notes that each method “may produce slightly different characteristics,” but all three answer to the same tubing standards and the same minimum pressure ratings: 160 psi at 73°F and 100 psi at 180°F. Some tubing also carries an 80 psi rating at 200°F.

Read the printline before buying fittings

ASTM F876 and CSA B137.5 require markings at least every 5 feet. For a repair, four of them matter most:

  • Fitting systems. The printline lists the fitting standards the tubing maker approves, such as F1807 (metal insert with copper crimp ring), F1960 (cold expansion with a PEX reinforcing ring) or F2080. PPI warns: “Not all fittings are compatible with all PEX tubing.” Match the fitting to the printline, not to the letter.
  • Material designation code (“PEX” plus four digits). The first digit is the chlorine rating: 1 means up to 6 hours a day at 140°F, 3 means up to 12 hours, and 5 means continuous hot-water recirculation. If your house has a recirculating hot-water loop, this digit matters more than A or B.
  • UV rating (the second digit). This is the minimum outdoor-weathering exposure the tubing passed: 1, 3 or 6 months. Potable-water tubing must reach at least 1.
  • Pressure ratings at 73°F and 180°F, plus the potable-water certification mark.

Installation limits that apply to every type

  • Bend radius: PPI’s guide says not tighter than six times the tubing’s outside diameter, unless the tubing maker allows tighter.
  • Sunlight: keep PEX in its original packaging indoors, and do not install it outdoors unless it is buried or protected. PPI notes that UV damage is not visible. Cover pipe left exposed to daylight, as in an unfinished basement, with a UV-blocking sleeve or insulation the maker approves.
  • Water heaters: the model plumbing code text PPI quotes (604.13) bars PEX within the first 18 inches of piping connected to a water heater. Local code may differ, so check it.
  • Joining: PEX cannot be solvent-cemented or heat-fused. Every system uses mechanical compression, made with the tool its maker specifies.

Buying decision

For a repair, photograph the printline on the existing pipe. Buy fittings and a tool from the listed fitting standard, sized to the marked nominal size. For a repipe, choose a complete system (tubing, fittings, tool and warranty) that your plumber already installs and your local code accepts. The A or B letter matters less than that system match. For the material choice itself, see PEX vs copper .

This page summarizes industry documents. It is not an installation manual. The tubing maker’s instructions and local code govern any specific job.

Sources