Type K copper pipes are durable and made to last, due to their thick walls. The thickness of Type K pipes can vary based on the individual pipe's diameter: for instance, ½-inch Type K pipe has a wall thickness of .049 inches, while ¾-inch has a thickness of .065 inches. Because this type is thicker and heavier, it's also more expensive, making it a good choice for projects that require heft, such as commercial plumbing, HVAC, city water mains, and underground lines. Type K is available in flexible and rigid forms, and is usually identified by a green stamp.
Considered the most common type of copper piping, Type L copper pipes are often used for interior plumbing, swimming pools, some HVAC projects, and fire protection. These pipes are less expensive than Type K pipes, but are still very strong, with a wall thickness of .045 inches for a ¾-inch diameter. Type L copper pipes are marked with blue and come in both flexible rolls and rigid tubing. If your area has hard water, Type L is a good choice as the minerals won't wear away at the thicker walls as easily as Type M pipes.
Identified by red markings, Type M is the thinnest copper pipe listed here, with a wall thickness of .032 inches for a ¾-inch diameter pipe or .028-inch thickness for a ½-inch diameter pipe. Type M copper piping is often used for repairs, replacements, and extensions to interior water supply lines (if you need to fix a copper pipe leak, for instance); it is less rigid and easier to work with than pipes with thicker walls, making it a favorite of DIYers. It is also less expensive but is not always allowed by plumbing codes, so check with your local building authority or a local plumber before installing it.
DWV stands for "drain-waste-vent"-as that suggests, these pipes are used exclusively in drain and vent lines. You won't find copper DWV piping in newer homes; many contemporary construction projects rely on ABS plastic or PVC pipes vs. copper. Copper DWV pipes are only suitable for above-ground applications, and are never used in water systems as they only have a wall thickness of .042 inches for a 2-inch pipe and can withstand just 15 psi of pressure. Copper DWV pipes are marked with yellow.
