PEX Installation Procedure Reference

Why this matters

PEX took over residential water supply in the last 20 years because it's faster to install than copper, freezes without bursting (mostly), and tolerates the alkaline / mildly acidic water that pinholes copper. But the three PEX types are NOT interchangeable on all connection systems, and a tool / fitting / pipe-type mismatch produces leaks that don't show up until the wall is closed. Knowing what to use where prevents the call-back of the year.

The three PEX types

PEX-A (peroxide cross-linked, Engel method) - Uponor (Wirsbo), Rehau, Mr. PEX

• Most flexible
• Shape memory: kink can be repaired with a heat gun (recovers original shape)
• Best for cold-climate applications (most freeze-tolerant)
• Used with cold-expansion fittings (ASTM F1960) - the pipe is expanded with a tool, fitting inserted, pipe shrinks back to grip
• Slightly more expensive

PEX-B (silane cross-linked) - most common brand-agnostic PEX you'll find at supply houses

• Slightly stiffer than PEX-A
• Kinks are permanent (cut out and replace)
• Used with crimp ring (ASTM F1807) or stainless steel pinch clamp (ASTM F2098) connections
• Most affordable

PEX-C (irradiation cross-linked) - less common

• Stiffest of the three
• Same connection options as PEX-B (crimp / pinch)
• Mostly displaced in the market by PEX-B

Critical: PEX-A's cold-expansion fittings (F1960) do NOT work on PEX-B. You'll think the fitting is set, the pipe will pull off in your hand a day later. Match the fitting system to the pipe type.

Connection methods

Push-fit is acceptable for repair work and accessible locations but most plumbers avoid for inside-wall connections - long-term reliability is acceptable but harder to inspect.

Sizing and capacity

PEX is sized by nominal OD same as copper:

• 3/8" - fixture lines (less common; most fixtures take 1/2")
• 1/2" - standard fixture supply, branch runs
• 3/4" - trunk lines, hot water supply, larger fixtures
• 1" - main runs, large multi-fixture branches

ID of PEX is slightly less than copper of same nominal size, so use one size up for long runs where flow matters (e.g., 3/4" PEX runs longer than 1/2" copper for the same fixture flow). Many manifold systems home-run 1/2" PEX directly to each fixture, eliminating the trunk-branch sizing question.

Code requirements

• Bend radius: minimum 6× the OD for cold bends. 1/2" PEX = 3" radius minimum. Tighter requires a bend support (a metal or plastic guide bracket).
• Distance from heat source: PEX must be at least 18" from a water heater outlet (IPC 605.4). The first 18" of hot supply from the heater must be copper, CPVC, or metal flex.
• UV exposure: NEVER expose PEX to sunlight. Degradation is rapid (months). Bury, conceal, or wrap.
• Support spacing: horizontal max 32" between supports for 1/2" and 5/8" PEX (NEC P2904.5). Sagging causes air pockets and noise.
• Direct burial: allowed in many jurisdictions; check local AHJ. PEX is not technically rated for above-grade exterior in many code interpretations.
• Fittings between concealed connections: every code-cycle allows manifold and certain inline fittings inside walls; verify with local AHJ. Push-fit fittings are concealment-restricted in some areas.

Procedure - PEX-A cold-expansion (F1960) connection

Tools: Expansion tool (Milwaukee M12 ProPEX or Uponor manual), expansion head (matched to fitting size), the fitting itself, plumb scissor/blade cutter (PEX cutter).

1. Cut PEX square with a PEX cutter - perpendicular cut, no burrs. A ragged cut won't seal.
2. Slide the expansion ring (sleeve) over the PEX end. The ring is what creates the compression seal after the tool releases.
3. Insert expansion head into the PEX end. Pull the trigger / squeeze the handles - the head expands, pulling the PEX to a larger diameter. Quickly remove the head.
4. Insert the fitting into the now-expanded PEX. The PEX shrinks back around the fitting in 2-30 seconds (warmer ambient = faster).
5. Wait for full shrink-back - the ring should be flush against the fitting flange. Pull-test if you're unsure.

Critical: do NOT expand and then wait - re-expand. Cold-weather expansion (sub-50 °F) needs additional dwell time; warm the pipe with a heat gun if temp is low.

Procedure - PEX-B crimp ring (F1807) connection

Tools: Crimp tool (Apollo, Milwaukee, etc.), go/no-go gauge, copper crimp ring (matched to PEX size), the fitting.

1. Cut PEX square. Deburr if needed.
2. Slide crimp ring onto the PEX end about 1/4" from the end.
3. Push PEX onto fitting until fully seated against the shoulder.
4. Slide ring down so it sits 1/8"-1/4" from the end of the PEX.
5. Crimp with the tool. One firm squeeze, fully closing the handles.
6. Verify with go/no-go gauge. This is the step that catches under-crimping. Gauge fits = crimp acceptable. Gauge doesn't fit = re-crimp or cut and redo.

Manifold vs trunk-and-branch

Two PEX system layouts:

Trunk-and-branch: main 3/4" line runs through the building, 1/2" branches T off to each fixture. Looks like traditional copper. Saves PEX footage. Each fixture is fed from a tee.

Home-run (manifold): central manifold (usually near water heater), individual 1/2" lines run home-run-style to each fixture. Each fixture gets its own shutoff at the manifold. More PEX, but each line is independent - one frozen line, one slow run, one repair doesn't affect any others. Becoming the modern standard.

Manifolds: Viega ManaBloc, Sioux Chief MidlinE, Uponor manifold. Sized by fixture count.

Common installation mistakes

References

• ASTM F1960 (cold-expansion connections)
• ASTM F1807 (copper crimp ring connections)
• ASTM F2098 (stainless steel pinch clamp connections)
• IPC 605 (water supply, pipe and tubing materials)
• IRC P2904 (PEX support and installation)
• Manufacturer installation manuals (Uponor, Rehau, SharkBite, Apollo)