Although M and L copper pipes have the same outside dimensions, the interior walls of type L are thicker. Type M is typically used in personal homes, while the heavier-duty L pipes are used for projects such as commercial buildings, hot water heating systems and underground structures. Building inspectors should be consulted before a type of copper pipe is selected, because some areas have certain restrictions.
Copper has long been used by humans. Ancient people fashioned tools, weapons and decorations out of the metal. Cooper piping, too, has been around for centuries. Five thousand years ago, the Egyptian Pharaoh Cheops had copper pipes carry water to his bath. Modern copper pipes are easily distinguished by incised markings that indicate the type of pipe, the manufacturer and the country of origin. This information is also stamped right on pipes, and each type of pipe is assigned a different color. Installers use the same techniques and tools for both types of pipes. Type M is less expensive, though both versions typically have long lives. Occasionally, the thicker L pipes are preferable in residential homes, because acidic water is corrosive to copper. In this case, however, CPVC pipes or PEX versions, which are flexible plastic pipes, often hold up even better to this kind of water.