The Most Common Types of Copper Piping
Copper pipes are commonly used in the construction industry for water supply lines and for refrigerant lines in HVAC (heating, cooling, and air-conditioning) systems. Copper pipes can be manufactured as soft or rigid copper and offers excellent corrosion-resistance and reliable connections. The three most common types of copper pipe used in residential and commercial construction are Type K, Type L, and Type M. A fourth type, used for drain-waste-vent, or DWV, piping, can be found in some older homes.
Copper Pipe Sizing
The actual outside diameter (OD) of rigid copper type is always 1/8 inch larger than the nominal size, or what the pipe is called. For example, a "1/2-inch" copper pipe has an outside diameter of 5/8 inch. This is true with all three common types of new pipe, K, L, and M. The inside diameter (ID) of copper pipe is determined by the wall thickness of the pipe, which varies by the pipe type. The type of copper piping specified for any application may be determined by the internal or external fluid pressure, the installation, the service conditions, and the local building code requirements.
Type K Copper Pipe
Type K copper pipe has the thickest wall of all the common types. It is used for water distribution, fire protection, oil, HVAC, and many other applications in the construction industry. Type K pipe is available in rigid and flexible form and can be used with flared and compression fittings. It is recommended for main water lines and for underground installations because its thickness helps it withstand the pressure from backfilled earth in trenches. Type K pipe is not approved for use in natural gas applications because the gas environment can damage the joints of the pipes.
Type L Copper Pipe
Type L copper pipe is used for interior plumbing, fire protection, and some HVAC applications. It is available in rigid and flexible forms and can be used with sweat, compression, and flare fittings. Type L is considered the most common type of copper piping, as it can be used in many more applications than Type K. Flexible Type L copper can be used to repair or replace old water lines, although rigid tubing is more durable. Type L also can be used outside the home where it will be directly exposed.
Type L copper is thinner than Type K but thicker than type M.
Type M Copper Pipe
Copper pipe type M wall is thinner than both type K and L copper. Sold in both rigid and flexible forms, Type M is used most commonly for domestic water service and vacuum systems. It can be used with sweat, compression, and flare fittings. Type M tubing is favored for residential work for its relatively low price; a thinner wall means less copper and thus a lower price. Type M copper is not allowed by plumbing codes in all areas and applications. Always check with the local building authority for restrictions on its use.
Copper DWV Piping
Copper pipe for plumbing drains and vents was used in many old homes and has been all but replaced with PVC or ABS plastic pipe in modern construction. It is suitable only for above-ground applications and has a low-pressure rating of 10 to 15 pounds per square inch (psi), much lower than the water pressure of most municipal water supply systems. DWV pipe usually has yellow markings to distinguish it from M type copper.