PEX-A is the more flexible and kink-forgiving of the two, and it uses expansion fittings that restrict flow less. PEX-B is stiffer and cheaper and uses crimp or clamp rings that are fast to make. Both are cross-linked polyethylene, both meet the same ASTM standard for potable water tubing and both are used in repipes. If you are weighing a bigger decision, see the guide on repiping a house in Los Angeles.
What is the difference between PEX A and PEX B?
The letters name how the polyethylene is cross-linked during manufacturing, and that sets how the pipe behaves. PEX-A uses the Engel method and has shape memory, so it relaxes after bending. PEX-B uses the silane method and is stiffer. Both are rated to the same pressure and temperature under ASTM F876: 80 psi at 200 degrees Fahrenheit.
In practice, PEX-A bends in a wide arc without a fitting, can often be warmed with a heat gun to fix a kink and is more forgiving of freezing. PEX-B holds a bend more firmly, and a kinked section is usually cut out and spliced. The difference is real but small to a homeowner, and plumbers have strong habits, so many choose the type they know best.
Is PEX A or B better for a house repipe?
Neither is better across the board. PEX-A has an edge for tight walls and long flexible pulls, because it bends and kink-repairs. PEX-B has an edge on price and speed with crimp rings. A well-installed system in either type outlasts a poorly installed system in the other, so the plumber matters more than the letter.
For an older Los Angeles house with plaster walls and narrow chases, flexibility helps. PEX-A needs less cutting, and fewer access holes mean less patching. For an open attic run in a newer house, the savings from PEX-B can be the better deal. Ask the plumber why they favor one, and ask for the brand and fitting type in writing so you know what is in the wall.
Does PEX A or B have better fittings?
PEX-A uses cold expansion fittings (ASTM F1960), where the pipe is stretched over a fitting and shrinks back to grip it. The fitting does not narrow the opening much, so flow loses less. PEX-B uses crimp or cinch ring fittings (ASTM F1807 and F2098) over an insert that does narrow the opening a little.
You can use crimp or clamp rings on PEX-A as well, which gives up the flow advantage. Expansion fittings are made for PEX-A and are not reliable on PEX-B. Every fitting is a possible leak point, so fewer fittings and a clean install matter more than the pipe label. Ask whether the plumber uses a manifold, which cuts the number of joints in the walls.
Expansion tools cost more, and the pipe needs time to contract before it holds full pressure, which is slower in cold weather. In Los Angeles that rarely matters, but it is part of why some plumbers stay with crimp.
Which is cheaper, PEX A or PEX B?
PEX-B is usually cheaper, because the pipe costs less and crimp tools are cheaper than expansion tools. PEX-A carries a premium on the pipe and the tooling. On a whole house, the pipe is a small share of the bill, and labor is most of it, so the gap you see on a quote is often modest.
Published cost guides put a PEX repipe on a 2,000 square foot, two-bath house at roughly $4,000 to $10,000 without splitting out A and B. Do not assume the cheaper quote is B, or that B is a worse system. Ask for the line items, as laid out on PEX repipe cost, and compare what is in them.
Which holds up better in cold or hot conditions?
PEX-A is the more freeze-tolerant, because its flexibility lets it expand when water freezes, but it is not burst-proof, and the fittings are the weak point. Both types resist chlorine and do not corrode. Neither should sit in sunlight, because ultraviolet light degrades PEX, so exposed runs outside need protection or a different material.
Hot attics are common in Los Angeles. Both types are rated for hot water, and recirculation lines near a heater need correct clearance. Local heat is not a reason to avoid PEX, but unprotected outdoor runs are. Hose bibs and exterior stubs are often copper for this reason. If you have an older heater, the page on PEX versus copper covers where copper is still the better pick.
Does the type matter for LADWP water and the permit?
Not much. LADWP is expanding chloramine across its system, and PEX resists chlorine-based disinfectants, but both types are listed for potable water. A Los Angeles repipe needs a LADBS plumbing permit and an inspection either way, and the inspector looks at the installation and the pressure test, not at the letter.
The one thing that does matter is that the pipe and fittings are approved for potable water and installed to the manufacturer's rules. Mixing brands of pipe and fittings can void a manufacturer warranty and can cause leaks. Check the plumber's license at cslb.ca.gov, and ask for the brand and fitting type to be named on the permit paperwork or the quote.
Common questions
Can PEX A and PEX B be mixed in one house?
Yes, if the right fittings are used on each. Crimp and clamp rings are approved for both types, and expansion fittings are made for PEX-A. A plumber might use one type for the trunk lines and another for short branches. Mixing is fine technically, but it adds confusion later, so ask for the layout to be noted.
Is PEX A stronger than PEX B?
Both meet the same pressure and temperature ratings. Some tests show PEX-B holding a little more burst pressure, and PEX-A is more flexible and kink-repairable. In a house at normal pressure you will not see a difference. The plumber's installation matters far more than the type.
Which PEX do most Los Angeles plumbers use?
It varies by plumber and by the job. Many use PEX-B with crimp rings for speed and cost, and others prefer PEX-A for tight old walls. We did not find a published split for Los Angeles, so ask the plumber what they use and why.
Does PEX leach chemicals into drinking water?
PEX sold for drinking water must meet NSF standards for potable water, and some new pipe can give a slight plastic taste that fades with flushing. California looked closely at this before approving PEX for the state plumbing code. If you have concerns, ask for the pipe's listing and flush new lines before drinking.
Can I install PEX myself?
A homeowner may be able to do their own work as an owner-builder in California, but a repipe still needs a LADBS permit and inspection, and fittings need the right tools. Our walk-through in how to repipe a house with PEX covers what is involved so you can decide.
For a written price on either type, use the quote page.