PVF Reference Library · Technical Reference

Copper Tube Types K, L, M and DWV

How to tell Type K, L, M and DWV copper tube apart by marking color and wall, why copper tube is sized differently from steel pipe, and where each type is normally used.

Ref PV-0007ASTM B88ASTM B306

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Copper water tube made to ASTM B88 comes in three wall thicknesses: Type K (thickest), Type L (medium) and Type M (thinnest). Within a nominal size, all three have the same outside diameter, so they take the same solder, press and push fittings. Only the wall and the ID change. Drain-waste-vent tube (DWV, ASTM B306) has an even thinner wall and is for non-pressure drainage only.

How to identify

Marking color: hard-drawn straight lengths are marked with a continuous colored ink line that shows the type, the manufacturer and the country of origin. Annealed (soft) coils are stamped rather than color-printed.
Size check: nominal to actual OD (in): 1/4 = 0.375, 3/8 = 0.500, 1/2 = 0.625, 3/4 = 0.875, 1 = 1.125, 1-1/4 = 1.375, 1-1/2 = 1.625, 2 = 2.125. In general the actual OD of copper water tube is the nominal size plus 1/8 in. For example, 1/2 in nominal tube measures 5/8 in (0.625 in) OD.
Wall check: compare the wall at a cut end against a known sample, or measure it with a caliper.
ACR tube (ASTM B280) is sized by its actual OD and is supplied cleaned and capped. See the ACR guide in the HVAC library.

Type comparison

Type	Marking color	Wall	Common uses	Temper available
K	Green	Thickest	Underground water service, high-demand lines	Hard (drawn) and soft (annealed)
L	Blue	Medium	Interior water distribution, hydronic, some gas (where permitted)	Hard and soft
M	Red	Thin	Interior water distribution where the code allows	Hard
DWV	Yellow	Thinnest	Drain, waste and vent only; not for pressure	Hard

Key points

Allowable working pressure depends on the type, size, temper, temperature and joining method. Brazing anneals the tube and lowers its rating compared with soldered or hard-drawn tube. Use the manufacturer's data or the Copper Development Association handbook, and the governing code.
Local plumbing codes decide which types are allowed underground, inside buildings and for fuel gas. Type M is not permitted everywhere.
Copper water tube is not the same size as copper pipe (IPS brass or copper pipe). Copper pipe uses steel pipe ODs.

Common mistakes

Measuring the OD (5/8 in) and selling 5/8 in ACR tube to a plumber who needs 1/2 in nominal Type L. The OD is the same, but ACR and water tube differ in cleanliness, capping and sometimes temper.
Using DWV tube in a pressurized line.
Assuming the marking color is optional. On hard tube it is the main way to identify the type in the field.

Governing standards: ASTM B88 (seamless copper water tube); ASTM B306 (DWV tube); ASTM B280 (ACR tube); ASME B16.22 and B16.18 (solder-joint fittings); local plumbing code (IPC or UPC as adopted).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

More in Technical Reference

← All PVF sheets