Copper pipes are commonly used in the construction industry for water supply lines and refrigerant lines in HVAC (heating, cooling, and air-conditioning) systems. Copper pipes can be manufactured as soft or rigid copper and offer 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. It 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 internal or external fluid pressure may determine the type of copper piping specified for any application, the installation, the service conditions, and the local building code requirements.
Common Types of Copper Piping
- 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 a rigid and flexible form and can be used with flared and compression fittings. It is recommended for main water lines and underground installations because its thickness helps it withstand the pressure from backfilled earth in trenches.
- 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 heating water services 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 always 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 commercial applications and has been all but replaced with PVC or ABS plastic pipe in modern construction. (For specific applications or uses, check your local code.) It is suitable only for above-ground applications and has a low-pressure rating, typically lower than the water pressure of most municipal water supply systems. DWV pipe usually has yellow markings to distinguish it from M type copper.