PEX Pipe Guide: PEX-A vs PEX-B vs PEX-C, Fittings, UV Limits and Cost

• PEX is cross-linked polyethylene, a flexible plastic pipe used for hot and cold drinking-water supply lines in homes. The tubing is made to the ASTM F876 standard (Plastics Pipe Institute).
• PEX-A, PEX-B and PEX-C are named for how the polyethylene is cross-linked, not for quality grades. PEX-A is the most flexible, PEX-B is stiffer and usually cheaper, and PEX-C is less common.
• Fittings: crimp rings and stainless clamp (cinch) rings work on all types; expansion fittings work on PEX-A only; push-to-connect fittings work on any type.
• Sunlight: PEX is damaged by ultraviolet light. Allowed exposure before installation varies by manufacturer and product, commonly a few weeks to several months, so check the printed limit on the tubing or its data sheet. Never use it outdoors uncovered.
• Versus copper: PEX is generally cheaper per foot and faster to install, resists pinhole corrosion, and tolerates some freezing, but it is not freezeproof.
• Gas lines and main service lines: do not use drinking-water PEX for gas, and ask a licensed plumber and your local code office before connecting to the main water service or a water heater.

All three are cross-linked polyethylene. The letter reflects the manufacturing method:

• PEX-A is cross-linked during manufacture (the Engel method), giving the most uniform cross-linking and the most flexibility. It has shape memory, so a kink can often be repaired by warming it with a heat gun rather than cutting it out. It is the only type that works with cold-expansion fittings. It usually costs a bit more per foot.
• PEX-B is cross-linked by moisture (silane) after extrusion. It is stiffer, with larger bend radius, but is widely available, usually the least expensive, and has good resistance to chlorinated water in many products. A kink cannot be heat-repaired and the section must be cut out.
• PEX-C is cross-linked by electron-beam irradiation. It is flexible and affordable but harder to find in stores and has the same fitting options as PEX-B.

For most DIY and plumber repairs, any of the three is acceptable when it carries the right ASTM and NSF marks. The decision usually comes down to the fitting system you prefer, how tight the bends are, and what your local supplier stocks. Whichever you choose, use tubing and fittings from the same manufacturer system when its instructions say to, because fittings are matched to specific tube dimensions.

Choose by cost, temperature, local code and how much of the house you are plumbing:

• PEX: flexible, fewer fittings, quick to run through walls, resists scale and pinhole leaks, and is usually cheaper than copper. It must be protected from UV and from contact with solvents, some chemicals and hot flue surfaces.
• Copper: long-lived, rigid, proven for decades, fire-resistant and UV-proof, but more expensive and slower to install because it is sweat-soldered, and aggressive water can cause pinholes. Our guide to the most common plumbing problems covers pinhole leaks.
• CPVC: rigid plastic joined with solvent cement. Cheaper than copper, but it can become brittle with age and heat and crack, especially in some installations, so many plumbers now prefer PEX or copper for new work.

Typical ratings: PEX is commonly rated at 160 psi at 73°F, 100 psi at 180°F and 80 psi at 200°F, but always read the markings on your tubing.

The fitting system matters more to your project than the tube type:

• Crimp rings (copper): a copper ring is squeezed around the tube and a barbed insert. Tool is inexpensive. Check every joint with a go/no-go gauge.
• Clamp (cinch) rings (stainless): a stainless band tightened with one tool that fits several sizes. Easier in tight spaces and the tool is more forgiving.
• Expansion (cold-expansion, ASTM F1960): the tube and a ring are expanded, then the fitting is inserted and the tubing shrinks back around it. Very reliable and gives a full-flow connection, but works with PEX-A only and uses a more expensive tool.
• Push-to-connect (e.g. SharkBite-type): no tools; the fitting pushes on and grips the tube. Great for repairs and transitions between PEX, copper and CPVC, though per-fitting cost is high and most plumbers use them for repairs rather than whole-house runs. Follow the maker’s instructions on cutting, deburring and insertion depth.

UV (sunlight). Polyethylene degrades in ultraviolet light. Manufacturers state a limit for exposure to sunlight during storage and installation, and that limit varies by product, so read the printed text on the tube or the data sheet. Store coils in their box or bag, and cover exposed tubing. PEX is not made for permanent outdoor use unless the maker specifically says otherwise.

Freezing. PEX can expand a little when water freezes, so it often survives a freeze that would split copper, but it is not freezeproof, and fittings can still split. Insulate pipes in unheated spaces and follow our guide to winterizing pipes.

Heat and flues. Do not run PEX close to a flue, recessed light, or a gas water heater’s hot surfaces. Many codes and manufacturers require a metal or approved connector for the first section at the water heater. Follow the instructions and local code.

Chemicals. Keep PEX away from petroleum products, solvents, paints and some pipe thread sealants and insulation; ask the manufacturer’s compatibility list. Chemicals can permeate or weaken the wall.

Prices change often, so confirm locally, but as a general guide:

• Tubing: PEX usually costs much less per foot than copper; ½-inch PEX is often in the range of a dollar or less to a bit over a dollar per foot, depending on type, brand and coil size.
• Fittings and tools: crimp or clamp tools are cheap to modest; expansion tools and cases cost more. Push-fit fittings cost several dollars each.
• Whole-house repipe: a licensed plumber’s quote often runs from a few thousand dollars to well over $10,000 depending on the size of the home, number of bathrooms, and access. Get at least three written quotes and ask what drywall repair is included.

Cost is not the only issue. Ask whether your city requires permits and inspections for repiping, and avoid DIY work on the main water service and water heater connections unless you are licensed or the code allows it.

1. Shut off the water and drain the lines.
2. Plan the run: use gentle bends, keep within the minimum bend radius (about six times the outside diameter is a common minimum, so confirm in the instructions), and support the tubing with approved clips or hangers.
3. Cut square with a PEX cutter, not a saw, and deburr as the instructions require.
4. Make the joint with the fitting system you chose and the matching tool.
5. Check the joint with a go/no-go gauge for crimps, or visually for clamps and expansions.
6. Pressure test as local code requires before closing walls, and look for drips again after 24 hours.

Hire a licensed plumber for the connection to the municipal main or well line, for anything involving gas, and when your jurisdiction requires a permit. Pipes in walls are hidden, so quality workmanship matters.

• Plastics Pipe Institute (PPI): PEX industry information
• U.S. Department of Energy: Energy Saver Guide (water heating)