Manufacturers make hard and soft copper pipe for water supply plumbing. Soft copper pipe bends easily without tools and is more properly called tubing. Inflexible hard copper pipe requires pipe bending equipment in order to bend it and is usually cut and fit rather than bent. Most residential water supply plumbing uses two types of hard copper pipe called type M and type L.
Types M and L copper pipes are both used as water supply lines, but type M pipes are thinner and have a lower pressure rating than type L pipes.
Copper Pipe Types
Manufacturers provide copper pipe in four standardized types: K, L, M, and DWV. The letters indicate, in part, the relative thickness of the pipe wall from thickest to thinnest. The actual wall thickness depends on the size of the pipe.
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The letter codes also relate to the color of the printing placed on the side of the pipe, which helps to identify it. Type K is green, type L is blue, type M is red, and DWV is yellow. Type L pipe may be referred to as blue, and type M is often referred to as red.
Uses of Copper Pipe Types
All the pipe types are suitable for use as plumbing, but DWV may not be used for water supply pipe since it has no pressure rating. Type K, or green copper pipe, is the only one suitable for burial and is often used to bring the water supply into a home.
Types M and L make up the water supply pipes in homes. Type L has thicker walls and a higher pressure rating. Some local codes specify that only type L is allowed and that type M is not allowed. The International Building Code allows both L and M, as well as type K for use as water supply pipe.
Differences Between Types M and L
The main difference between type M and L is the wall thickness and pressure rating. The two most common sizes are half-inch and three-quarter-inch. Type M half-inch pipe has a wall thickness of 0.028 inches while type L is 0.040 inches. Type M three-quarter-inch pipe has a wall thickness of 0.032 inches and type L is 0.045 inches.
Type L costs more than type M. Type L with its thicker walls weighs more and requires more copper, thereby costing more to manufacture and also to transport.
Copper pipes of the same type and size all have the same outside diameter, which allows them to use the same fittings for connections. The inside diameter varies by type due to the different thickness of the walls. For example, half-inch type M has an inside diameter of 0.569 inches and type L is 0.545 inches.
Type M vs. Type L Suitability
Copper pipe for indoor residential water supply lines may be either type M or type L, unless local codes specify otherwise. Both are rated well above common water pressure levels found in municipal water supply systems. The higher cost of type K pipe usually restricts it to the buried pipe bringing water into a home.
The cost difference of type M versus type L is enough that it makes sense for most homeowners to use type M instead of type L for large projects. Always check your local code requirements for building materials and permits before starting projects or buying building materials.