Pipe Sizing + Material Reference
Why this matters
Wrong pipe material = code violation, wrong size = poor flow + customer complaint. Each material has applications + limits + connection methods. The plumber who knows the differences cold installs the right system the first time. This is the field card.
Pipe materials overview
| Material | Use | Joining | Cost | Lifetime |
|---|---|---|---|---|
| Copper Type L | Supply (hot + cold) | Solder, press, compression | High | 50+ yr |
| Copper Type M | Supply (light residential) | Solder, press | Mid | 30 - 40 yr |
| PEX | Supply | Crimp, press, expansion | Mid | 50+ yr |
| CPVC | Supply | Solvent weld | Low | 20 - 40 yr |
| PVC | DWV, irrigation | Solvent weld | Low | 50+ yr |
| ABS | DWV | Solvent weld | Low | 50+ yr |
| Cast iron | DWV (older) | Hub + spigot, no-hub | High | 75+ yr |
| Galvanized | Supply (older) | Threaded | Mid | 30 yr |
| Black iron | Gas | Threaded | Mid | 50+ yr |
Copper sizing
Type K (thickest wall): underground service, durability priority.
Type L (medium wall): standard residential supply. Sweat-soldered, press-fitted, OR compression.
Type M (thinnest acceptable): light residential supply only; not for high-pressure.
DWV copper (thinnest, non-pressure): drainage in older homes.
Standard sizes (nominal inch):
- 1/2" (5/8" OD): kitchen, bath supply runs
- 3/4" (7/8" OD): main supply branches
- 1" (1-1/8" OD): main supply to house
- 1-1/4", 1-1/2", 2": commercial + main service
Flow rate (Type L):
- 1/2": ~ 5 GPM safe
- 3/4": ~ 11 GPM safe
- 1": ~ 20 GPM safe
PEX sizing
Color code:
- Red: hot
- Blue: cold
- White: either, used where the installer wants one stock item
- Orange: commonly hydronic radiant tubing with an oxygen barrier
The color is a convenience, not a listing. The pipe's printed legend is what tells you the standard, the size, the pressure and temperature rating and the listing marks, and that legend is what an inspector reads.
PEX is not a fuel gas material. The yellow plastic pipe used for buried gas service is polyethylene gas pipe to ASTM D2513, a completely different product with its own fusion or mechanical fittings and its own qualified-installer requirements. Do not let the word "yellow" bridge those two things in anyone's head.
Brands:
- PEX-A (Uponor / Wirsbo): cross-linked + expansion-friendly; flexible
- PEX-B (Viega, Apollo, Watts): cross-linked but stiffer; crimp/clamp
- PEX-C: less common
Connection methods:
- Crimp (copper ring): pre-2000 standard; needs crimp tool
- Clamp (Oetiker stainless): cinch tool; reusable, easier inspection
- Expansion (PEX-A only): expand pipe + insert fitting; cold-weather seal
- Push-fit (SharkBite): no-tool; quick repair; expensive per fitting
Sizes: 1/4" - 1" residential common; smaller ID than copper of the same nominal size, so go one size up in PEX to match a copper run.
Limits: outdoor UV degradation; install must be protected from sunlight.
CPVC sizing
CTS (Copper Tube Sizing): 1/2", 3/4", 1" common.
Connection: solvent-weld with primer + CPVC cement (clear OR orange).
FlowGuard Gold: orange-colored common brand.
Use: cold water supply; some hot OK (rated to 180°F).
Limits: brittle in cold; UV-damaged; some areas restrict (check local code).
PVC sizing (DWV + irrigation)
Schedule 40 (white): pressure + DWV.
Schedule 80 (gray, thicker wall): higher pressure.
Standard DWV sizes: 1-1/4", 1-1/2", 2", 3", 4".
Connection: solvent-weld with PVC primer (purple OR clear) + PVC cement.
ABS sizing (DWV)
Black, slightly less brittle than PVC. Solvent-weld with ABS cement (no primer). Standard sizes match PVC.
Not interchangeable with PVC at solvent welds without transition cement.
Galvanized iron (legacy)
Threaded joints; thread paste OR PTFE tape.
Problem: corrosion narrows ID over decades (50% capacity loss common).
Service work: re-pipe to PEX OR copper rather than patch.
Black iron pipe (gas)
Threaded with pipe dope OR yellow gas-rated PTFE.
Sizes 1/2", 3/4", 1", 1-1/4"+: sized by demand + length per NFPA 54.
Cast iron (DWV in older homes)
Hub + spigot: oakum + lead-pour OR lead-and-oakum.
No-hub: neoprene gasket + stainless band clamp (modern; faster).
Cast iron service is quieter than PVC; some upscale new construction uses cast iron for DWV.
Pipe sizing rules of thumb
Supply sizing per fixture units + simultaneous demand: 1/2" branch 1 - 2 fixtures; 3/4" branch 3 - 5 fixtures; 1" main whole-house up to 6 - 8 fixtures simultaneous.
DWV per drainage fixture units (DFU): 1-1/4" branch 1 DFU (small lav); 1-1/2" 1 - 3 DFU; 2" 6 - 8 DFU; 3" 20 - 35 DFU (toilet + group); 4" main 60 - 200+ DFU.
Pipe support spacing
These come from the hanger-spacing table in the plumbing code (IPC Table 308.5 and its equivalents). Read the horizontal and vertical columns separately; they are not close to each other and swapping them is the usual mistake.
| Material | Horizontal | Vertical |
|---|---|---|
| Copper, 1-1/4" and smaller | 6 ft | 10 ft |
| Copper, 1-1/2" and larger | 10 ft | 10 ft |
| PEX | 32 in | 10 ft |
| CPVC, 1" and smaller | 3 ft | 10 ft |
| CPVC, 1-1/4" and larger | 4 ft | 10 ft |
| PVC and ABS | 4 ft | 10 ft |
| Cast iron | 5 ft (10 ft where 10 ft lengths are used) | 15 ft |
Vertical piping also gets support at every story regardless of the number in the column. Verify against the table in the edition your AHJ adopted before you hang a job to these figures.
Joining methods
Sweat solder: traditional copper joining. 95/5 solder + flux + heat. Strong, reliable, slow.
Press-fit (Apollo, Viega ProPress, NIBCO): copper jointed with stainless ring + ProPress tool. Fast, no flame. The tool is a significant up-front purchase and the fittings cost more per joint than sweat, so it pays off on volume and on jobs where an open flame is not an option.
Compression (brass): ferrule compresses around copper tubing. Reusable for service.
Crimp PEX: copper ring + crimp tool.
Cinch PEX: stainless clamp + cinch tool.
Expansion PEX-A: expander tool stretches pipe; fitting inserted; pipe shrinks back.
Solvent weld (CPVC, PVC, ABS): primer + cement; chemical bonding.
Threaded: NPT (National Pipe Tapered) for iron + brass. Pipe dope OR PTFE.
Common pipe material mistakes
Wrong material for application (PVC supply lines = code violation in most jurisdictions). Wrong cement (PVC cement on CPVC; ABS cement on PVC; won't bond). PEX in direct sunlight (UV degrades; install protected). Galvanized used new (long-term corrosion). Black iron for water (rusts inside).
Mixed metal connections (copper + galvanized): dielectric union required to prevent galvanic corrosion.
Common service scenarios
Failed galvanized supply line: repipe with PEX-A (fastest); whole-house 1 - 2 days work.
Slab leak (under concrete): re-route around slab with PEX OR copper.
Corroded copper from acidic water: install water softener + repipe affected section.
Frozen pipe burst: PEX more freeze-tolerant than copper; insulate + heat tape.
Truck stock by trade
Plumbing: copper assortment (1/2", 3/4", 1"), PEX (1/2" + 3/4" red + blue), CPVC (1/2" + 3/4"), PVC fittings DWV, brass compression fittings, solder + flux + cleaner.
HVAC: copper (1/2", 5/8", 7/8") for refrigerant lines, soft + hard copper depending on application.
Insulation
Pipe insulation (foam) on hot water supply for efficiency + freeze protection on cold lines in exterior walls. R-3 to R-6 typical.
The single most-useful pipe-material habit is the CHECK LOCAL CODE before quoting. Some jurisdictions don't allow CPVC OR push-fit fittings (SharkBite) for permanent residential applications; some require copper for any line over 5 PSI; some require PEX-only for slab installations. Don't quote a job assuming national-standard materials work everywhere - pull the local code OR call the inspector before committing materials. 5 minutes verification saves a rip-out + re-pipe.
References
- IPC Chapter 6 (Water Supply)
- IRC Chapter 29 (Plumbing Materials)
- ASTM F876, F877 (PEX standards)
- ASTM B42 (Copper pipe standards)
- ASTM D1785 (PVC pipe), D2846 (CPVC)
- Manuall internal: Water Pressure + Flow, Soldering + Brazing