Plumbing · Compare
PEX vs copper pipe: which to run for water distribution
PEX wins on cost and install speed for most branch runs; copper still earns its place in high heat, exposed, and spec-driven work.
Short answer
For most interior potable water distribution, run PEX. It is cheaper in material and labor, goes in fast with fewer joints and no flame, and does not suffer the erosion corrosion that pinholes copper on hot recirculation. The single deciding factor is the environment and spec: copper is the pick where the pipe is exposed to UV or high heat, where the friction budget is tight enough that copper's larger inside diameter holds a size, or where the jurisdiction or project spec calls for it.
PEX vs Copper pipe: side by side
| Factor | PEX | Copper pipe |
|---|---|---|
| Upfront cost | Lower material cost, faster labor, no torch | Higher material cost and skilled soldering or press labor |
| Install speed and method | Flexible, long runs with few joints, no open flame | Rigid, cut and ream then solder or press, slower |
| Inside diameter and friction | Thicker wall, smaller ID at same nominal size, higher velocity and friction, often size up | Larger, smoother bore when new, can hold a size on a tight budget |
| Friction over time | Plastic bore holds its smoothness (C near 150) | C starts near 150 but falls as the wall scales and corrodes; old copper runs rougher than the chart |
| Fittings | Insert fittings neck the bore at every joint, large added equivalent length; use large-bore systems on demanding runs | Lower fitting restriction, less equivalent length per joint |
| Velocity and erosion | Not subject to erosion corrosion; still holds 8 ft/s cold, 5 ft/s hot | Erosion corrosion pinholes at elbows; drop to 2 to 3 ft/s above 140 F, near 4 ft/s in low-pH water |
| Hot recirculation | Tolerates loop service; keep to the 5 ft/s hot limit | Classic place copper erodes through years early if loop velocity runs high |
| Code and sizing basis | Size off the manufacturer's flow and pressure-drop data, not a copper chart; IPC Ch. 6 / App. E or UPC | Size off the copper tube handbook and code tables; same IPC / UPC rules |
| Best use | Long branch runs, remodels, retrofits, freeze-prone or aggressive water | Exposed or UV runs, high-temperature service, mechanical rooms, spec-required |
Which should you pick?
Choose PEX when
- Long flexible branch runs, remodels, and retrofits where you want few accessible joints and no flame near combustibles
- Cost- and labor-sensitive jobs where speed of install drives the bid
- Aggressive, low-pH water that pinholes copper, or freeze-prone locations
- Just size up or use large-bore fitting systems on long or busy runs, and size off the maker's flow data
Choose Copper pipe when
- Exposed, UV-exposed, or high-temperature runs where plastic is a poor fit
- Where the friction budget is tight and copper's larger inside diameter holds a size
- Where the jurisdiction, project spec, or mechanical room detail calls for copper
- Where proven longevity and recyclability matter, keeping hot recirc velocity down to avoid erosion
Bottom line
It depends on the water, the temperature, the exposure, and the spec. PEX is the modern default for interior distribution because it is cheaper, faster, and immune to the erosion corrosion that pinholes copper, but it runs a smaller inside diameter and restrictive insert fittings, so it often needs a size up and must be sized off the manufacturer's data rather than a copper chart. Copper still wins on exposed or high-heat runs, where a tight friction budget rewards its larger smooth bore, or where the code or spec requires it. Match the material to the run, not to habit, and hold the velocity limits either way.
FAQ
Does PEX need a bigger size than copper for the same flow?
Often yes. In the common copper-tube-size dimension, PEX has a thicker wall and a smaller inside diameter than copper of the same nominal size, so it runs a higher velocity and more friction at the same flow. Its insert fittings neck the bore down further at every joint. On a long or busy run, go up a size and size PEX off the manufacturer's flow and pressure-drop data, not a copper chart.
Why does copper get pinhole leaks?
Usually erosion corrosion. When velocity runs past the limit, the moving water strips the protective film off the inside of the pipe and grooves out the elbows and fittings where the flow turns, showing up as scalloped grooves and pinholes. It hits hardest on a hot recirculation loop run too fast, which erodes through years early. Aggressive, low-pH water worsens it, which is one reason to hold copper velocity down.
Is PEX or copper better for repiping?
For most repipes, PEX is easier and cheaper: it is flexible, runs long distances with few joints, needs no torch, and tolerates freezing and aggressive water better than copper. Copper is the better choice where the pipe is exposed or UV-lit, sees high temperatures, sits in a tight friction budget that its larger bore can hold, or where the local code or project spec requires it. Both must be sized to the demand and kept under the velocity limits.