PEX Plumbing: Types, Connections, and Installation for DIY Repipes

PEX Types: A, B, and C

PEX-A (Engel method) is the most flexible and has the best freeze resistance. It can be expanded with an expansion tool and returns to its original shape, making connections with expansion fittings. The flexibility makes it easier to route through tight spaces and around obstacles. PEX-A costs more per foot than PEX-B.

PEX-B (silane method) is slightly stiffer than PEX-A but still far more flexible than copper or CPVC. It works with crimp rings or cinch clamps. PEX-B is the most common type for residential plumbing, balancing cost and performance. It has slightly higher burst pressure than PEX-A.

PEX-C (irradiation method) is the stiffest and least common. It has the same connection options as PEX-B but is more prone to kinking. Most professional plumbers avoid PEX-C for residential water lines.

Color coding: red PEX carries hot water, blue carries cold, white carries either. The color is purely for identification — the material is identical regardless of color. You can use white for everything if you prefer a consistent look in exposed areas.

Connection Methods

Crimp connections: slide a copper crimp ring over the PEX, insert a brass fitting, position the ring over the fitting barb, and compress it with a crimp tool. This is the most common and least expensive method. You need a go/no-go gauge to verify each crimp — a properly crimped ring should pass the go side and not pass the no-go side.

Cinch clamp connections: similar to crimp, but use stainless steel cinch clamps instead of copper rings. The clamp tightens with a ratcheting cinch tool. Cinch clamps are slightly easier to install in tight spaces because the tool grips from one side only, unlike a crimp tool that must wrap around the fitting.

Expansion connections (PEX-A only): expand the end of the PEX tube with an expansion tool, slide it over a fitting, and the PEX contracts back to its original diameter, gripping the fitting tightly. No metal ring is needed. Expansion fittings have a larger bore than crimp/cinch fittings, so they restrict flow less — a real advantage for 3/8-inch and 1/2-inch lines.

Push-fit connections: SharkBite and similar fittings work with all PEX types (and copper and CPVC). No special tools needed — push the PEX into the fitting until it clicks. Expensive per fitting, but useful for quick repairs or transitions between PEX and copper.

Layout: Home Run vs Trunk-and-Branch

Trunk-and-branch mimics a traditional copper layout: a main line (trunk) runs through the house with smaller branch lines teeing off to individual fixtures. This uses less pipe but more fittings. Every fitting is a potential leak point and a flow restriction.

Home-run (manifold) layout: a central manifold with individual dedicated lines running to each fixture. Each fixture gets its own uninterrupted PEX line from the manifold, with no fittings between manifold and fixture. This uses more pipe but virtually eliminates fittings in walls and ceilings. Each line can be shut off independently at the manifold.

Most PEX installations use a hybrid approach: manifolds for the main distribution with short trunk-and-branch runs where routing individual lines is impractical. The manifold typically mounts in the mechanical room near the water heater.

For a full repipe, the home-run manifold approach is worth the extra pipe cost. Fewer hidden fittings means fewer hidden leak risks. The ability to shut off individual fixtures at the manifold (without affecting the rest of the house) is also a significant practical advantage.

Installation Best Practices

Support PEX every 32 inches on horizontal runs and every 4 to 6 feet on vertical runs. Use plastic hangers or padded clamps — never metal clamps that can cut into the tubing over time. PEX expands and contracts with temperature changes, so leave a slight curve in the line to accommodate movement.

Protect PEX from UV exposure. PEX degrades quickly in direct sunlight — most manufacturers void the warranty after 30 to 60 days of UV exposure. Cover any exposed PEX with pipe insulation or UV-rated sleeve where it passes through unconditioned spaces with sun exposure.

Do not install PEX within 18 inches of a water heater or any heat source above 200 degrees F. Use a copper stub-out from the water heater and transition to PEX with a push-fit or threaded adapter.

PEX cannot be directly connected to a water heater, boiler, or recirculation pump with temperatures above 200 degrees. Check the manufacturer's temperature and pressure ratings — most PEX is rated for 160 degrees at 100 PSI, or 73 degrees at 160 PSI. These ratings are adequate for residential hot water systems but not for radiant heating loops connected to high-temperature boilers.

PEX vs Copper: When Each Makes Sense

PEX wins on: cost (40 to 60 percent less per foot), installation speed, freeze resistance (PEX can expand without bursting in most freeze events), corrosion resistance (unaffected by acidic water or mineral buildup), and noise (PEX is quieter than copper — no water hammer).

Copper wins on: UV resistance (fine for outdoor use), code acceptance (some jurisdictions still require copper for certain applications), rodent resistance (rodents can chew through PEX but not copper), and longevity track record (copper systems have lasted 50+ years; PEX has been in widespread use since the 1990s).

Use copper for: the first 18 inches from a water heater, outdoor exposed runs, connections to gas appliances (PEX cannot carry gas), and any jurisdiction where PEX is not code-approved for the specific application.

Use PEX for: everything else in a residential water supply system. The cost savings, faster installation, and reduced leak risk (fewer fittings in a manifold layout) make it the clear choice for most residential plumbing work.

Frequently Asked Questions