PEX vs Copper vs CPVC: Which Water Supply Pipe to Run
PEX, copper, and CPVC water supply pipe compared — temperature and pressure ratings, expansion, freeze behavior, joining, and where each wins.
Updated August 20, 2026
Three materials dominate residential water supply piping, and they solve the same problem three different ways. PEX is a flexible polymer tube that pulls through framing like electrical cable and forgives freezes; copper is the rigid metal benchmark with a century of installed history; CPVC is a rigid plastic that glues together with solvent cement and shrugs off the chlorine in treated water.
The ratings tell the story of hot water. All three carry cold water indefinitely, but heat is where they separate: PEX is pressure-rated at 160 psi at 73.4 °F yet only 80 psi at its 200 °F ceiling, CPVC tube holds 400 psi cold but 100 psi at 180 °F, and copper tube itself barely notices domestic temperatures — its practical limit is the joint, not the wall. Movement follows the same ranking: a hot PEX run grows roughly an inch per 100 feet for every 10 °F of temperature rise, an order of magnitude more than copper.
None of the three wins outright, which is why repipes routinely mix them: PEX through the concealed runs, copper where pipe is exposed or near the water heater, CPVC where aggressive water chemistry would attack metal. The table below puts the published numbers side by side so the choice follows the service conditions rather than habit.
Side by Side
| Spec | PEX | Copper (Type L) | CPVC |
|---|---|---|---|
| Material & governing standard | Cross-linked polyethylene — ASTM F876/F877 | Seamless copper water tube, Type L — ASTM B88 | Chlorinated PVC — ASTM D2846 (CTS SDR-11) or F441 (schedules) |
| Pressure rating vs temperaturePlastic ratings are temperature-tied by definition; every listed pair is a published class rating, not a field observation. | 160 psi @ 73.4 °F, 100 psi @ 180 °F, 80 psi @ 200 °F (F876 class ratings) | Tube rates several hundred psi even hot — soldered-joint ratings, not the tube, set the practical limit | 400 psi @ 73 °F, 100 psi @ 180 °F (D2846 CTS); 180 °F is the intended service ceiling |
| Thermal expansion per 100 ft of runPublished coefficients: PEX ≈9 × 10⁻⁵, CPVC ≈3.2–5.5 × 10⁻⁵, copper ≈9.4 × 10⁻⁶ in/in/°F. | ≈1 in per 10 °F ΔT — the big mover; needs slack loops and loose supports | ≈1.1 in per 100 °F ΔT — smallest of the three | ≈3–4 in per 100 °F ΔT — offset or loop long hot runs |
| Freeze-damage tolerance | Flexible — often swells and survives a freeze, though fittings and repeated cycles still fail; not sold as freeze-proof | Rigid — ice expansion splits the tube wall | Rigid and notably brittle when cold — cracks rather than bulges |
| Joining method & tooling | Crimp/clamp rings or cold-expansion fittings; mechanical, no flame or cure time | Solder or braze (open flame), press fittings, or compression; skill- and prep-sensitive | One-step solvent cement for CTS sizes; simple tools but mandatory cure time before pressure |
| Chlorine & UV sensitivity | Chlorine resistance varies by listed class (F876 chlorine designations); UV exposure before installation is limited — check the print line | Unaffected by UV; can pit or erode in aggressive chemistry or sustained high velocity | Inherently chlorine-resistant (the polymer is chlorinated); surface UV-degrades outdoors unless painted |
| Service-life basis | Rated through long-term hydrostatic testing (PPI HSB listings); shorter field history than metal | Longest installed track record of the three — multi-decade service is routine | Long indoor record; ages toward brittleness, so old CPVC demands gentle handling at repairs |
Which One for the Job
Whole-house repipe on a budget
PEX
Continuous coils pull through joists and plates with a fraction of the fittings a rigid material needs, every joint is mechanical rather than flame- or solvent-made inside closed walls, and material cost per foot is the lowest of the three. Home-run manifold layouts are only practical in PEX.
Exposed mechanical-room and near-heater runs
Copper (Type L)
Exposed pipe wants rigidity, neat appearance, and indifference to UV and heat. Copper stays straight on its hangers and takes water-heater discharge temperatures without approaching a rating knee — and most PEX manufacturers require a metal lead-in near the heater connection anyway.
Recirculating hot-water loop
Copper (Type L)
A recirc loop holds pipe at temperature around the clock, the hardest duty for any plastic pressure class: hot, chlorinated, and continuous. Copper carries that service with margin as long as loop velocity is kept modest to avoid erosion; if plastic is used here, the design must respect the 100 psi @ 180 °F class limits, not the cold rating.
Regions with aggressive or low-pH well water
CPVC or PEX
Water chemistry that pits copper does not touch a polymer wall. CPVC adds inherent chlorine immunity for chlorinated systems; PEX adds freeze forgiveness for crawlspace runs. Between the plastics, pick by joining preference and exposure — neither corrodes.
Frequently Asked Questions
Why does PEX need to be kept away from the water heater?
Because the tank connection is the one place plumbing routinely exceeds PEX ratings: T&P discharge events and flue-adjacent surfaces run past the 200 °F / 80 psi class point. Most PEX manufacturers therefore require about 18 inches of metal piping off the heater before transitioning — check the specific installation manual, since the required distance is a listing condition.
Will a hard freeze always burst copper but spare PEX?
Not always, but the odds differ sharply. Ice expansion splits rigid copper and cracks cold-brittle CPVC, while flexible PEX usually swells and recovers. PEX is still not sold as freeze-proof — fittings, valves, and repeated freeze cycles can fail — so insulation and drain-down still matter in any material.
Can I glue CPVC with the same cement as PVC?
No. CPVC requires its own solvent cement — CTS sizes use a listed one-step CPVC cement per ASTM D2846 — because standard PVC cement does not develop full strength on chlorinated resin at hot-water temperatures. The cure schedule before pressurizing also depends on temperature and pipe size, so follow the cement label, not habit.
Which supply pipe is cheapest to install overall?
PEX, in most markets, and by more than the per-foot material spread suggests: coils eliminate most fittings, one worker can pull runs solo, and no flame means no fire watch or permit friction inside finished walls. Copper costs the most in both material and labor; CPVC lands between, cheap in material but fitting-heavy like all rigid pipe.
Try the Calculators
Sources
- ASTM F876/F877 and PPI Hydrostatic Stress Board listings — PEX class pressure ratings (160 psi @ 73.4 °F, 100 psi @ 180 °F, 80 psi @ 200 °F) and chlorine-resistance designations
- ASTM D2846/D2846M — CPVC CTS hot- and cold-water distribution systems (400 psi @ 73 °F, 100 psi @ 180 °F; solvent-cement joining)
- CDA Copper Tube Handbook (ASTM B88) — Type L tube ratings, joining methods, and expansion coefficient ≈9.4 × 10⁻⁶ in/in/°F
- PPFA CPVC installation handbook and manufacturer (FlowGuard/Lubrizol) technical data — CPVC expansion coefficient range and 200 °F strength derating