Copper pipes are commonly used in the construction industry for residential water supply lines and sometimes for drain and vent lines. Copper pipes can be manufactured as soft or rigid copper and they offer excellent corrosion resistance and reliable connections. While flexible PEX (cross-linked polyethylene) is now the more common choice for new installation and upgrades, copper pipe still has its place. It is considered a sturdier building material that has a longer lifespan—lasting up to 70 years. However, copper is about 60 percent more expensive than PEX, and it can be susceptible to cracking if the water inside the pipes is subject to freezing temperatures.
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, is found most often in some older homes. Below, we'll discuss how to choose the right copper pipe for your application.
|Type||Fitting Methods||Flexible form available||Common Use|
|Type K||•Soldered •Compression •Push-fit •Press-connect •Flare (flexible pipe)||Yes||Main water lines, underground lines|
|Type L||•Soldered •Compression •Push-fit •Press-connect •Flare (flexible pipe)||Yes||Branch water supply lines|
|Type M||•Soldered •Compression •Push-fit •Press-connect||No||Branch water supply lines|
|DWV||Soldered, Slip-joint||No||DWV plumbing lines|
What Is a Press-Connect Fitting?
A press-connect fitting is a flameless method of joining copper pipes, used mostly by professional plumbers. It uses special fittings with internal elastomeric gaskets (such as EPDM) to create a seal that withstands pressure. In the hands of pros, press-connect fittings are easy to make, but they require expensive hydraulic tools, so they are rarely used by amateurs. DIY homeowners who want a flameless connecting method are more likely to use push-fit connectors, such as Shark-Bite fittings.
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Type K Copper Pipe
Best for: Main water lines, underground installations.
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 forms. It is recommended for main water lines and underground installations because its thickness helps it withstand the pressure from backfilled earth in trenches.
Type K copper pipe is usually identified by a green stamp. It is an expensive form of copper pipe, and thus is not commonly used for interior water supply pipes.
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Type L Copper Pipe
Best for: Interior branch water supply lines.
Type L copper pipe is used for interior plumbing, as well as for fire protection, and some HVAC applications. It is available in rigid and flexible forms. 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 is the common choice for repairing or replacing old branch water lines. 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 L copper is usually identified by a blue stamp. This is the type that professional plumbers use for most indoor residential water supply lines.
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Type M Copper Pipe
Best for: Branch plumbing lines.
Type M copper pipe is thinner than both type K and L copper pipe. It is a common choice for repairs, replacements, and extensions to interior water supply lines. But Type M copper is not always allowed by plumbing codes in all areas, so check first with the local building authority. Where allowed, it is often favored for residential work because of its relatively low price—a thinner pipe wall means less copper and thus a lower price. It is a favorite of DIYers, who find it easy to cut and fit. But it is not available in a flexible form, as is type L.
Type M copper pipe is identified by red markings.
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Copper DWV Piping
Best for: Occasionally used for DWV (drain-waste-vent) pipes.
Copper pipe for plumbing drains and vents was used in many old homes and commercial applications, but it 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; it cannot carry the water pressure of most municipal water supply systems.
DWV pipe usually has yellow markings to distinguish it from other types.
Choosing Copper Pipe
Copper plumbing pipe (often known as tubing) comes in several types based on the thickness of the walls in the pipe relative to the diameter of the pipe. As outlined above, selecting the right copper pipe is really just a matter of matching the thickness of the pipe walls to the needs of the application. Type K has the largest wall-thickness to pipe diameter ratio and is usually used for underground applications where extreme strength is needed. At the other end, DWV grade has the lowest wall-thickness to pipe diameter ratio, making it suitable only for drain and vent lines that are under no pressure at all. In between, Types L and M are the pipes most often used for standard pressurized water supply pipes. In summary:
- DWV-grade: With a wall thickness of 0.42 in. for 1 1/2-inch pipe, this grade of copper pipe is recommended for above and below-ground drain, waste, and vent lines. However, given the expense of copper, it is rare to choose copper DWV pipe when PVC and ABS plastic is so much cheaper and easier to work with. An exception might be in exposed locations, especially vintage homes where there is a need to be consistent with historical practices.
- Type M: With a wall thickness of 0.28 in for 1/2-inch pipe, this grade of copper pipe is commonly used for residential water supply pipes. (It is also used in fire protection, fuel oil, HVAC, and vacuum system piping, though such uses are not common for DIY homeowners.) It is less expensive than thicker grades of copper, so where code allows for its use, it is the most popular choice for DIYers and professional plumbers making repairs or replacements to existing copper water supply systems in homes.
- Type L: With a wall thickness of. 0.40, this grade of copper pipe is also used for the same uses as Type M, but its extra thickness gives it the strength needed for natural gas lines. It can also be used in exposed above-ground outdoor locations, such as swimming pool or spa pipes. Where local codes have limitations on the use of Type M, this is the grade used for common repairs and replacements to existing indoor water supply systems.
- Type K: With a wall thickness of 0.65, this grade of copper pipe can be used for all the applications appropriate for types M and L, but because of its high cost, it is usually reserved for underground applications where great strength is required. It is not the usual choice for indoor plumbing repairs and replacements.
When purchasing pipe, be aware that the actual outside diameter (OD) of rigid copper pipe is always 1/8 inch larger than the nominal size—how the pipe is labeled. For example, a 1/2-inch copper pipe has an outside diameter of 5/8 inch. It is true with all three common types pipe, K, L, and M.
Increasingly, though, the choice for plumbing repairs and replacements is none of the above, but rather to use flexible PEX (cross-linked polyethylene) tubing—not only for new installations but also for repairs to existing systems. It is quite common for professional plumbers to patch in PEX whenever a branch plumbing line replacement is anything more major than a small repair. And DIYers are increasingly able to use PEX tubing and fittings themselves, although it was once the territory of professionals only.
However, if you wish to keep your plumbing system uniform, copper pipe is still widely used, and any plumber will be able to install it.