Gary Sprague | posted on July 28, 2020 at 12:00 PM

Copper pipes have been used as household water supply pipes for decades, and you may have seen them under cabinets or overhead in basements. Most people know that pipes have different diameters, but you may not realize that certain types of copper pipes are thicker than others. Understanding the differences between copper pipe types and the best applications for each type will help you make an informed choice when starting a plumbing repair or refurbishment project at home.

Among all copper tube types, the K-shaped tube has the thickest wall and the most durable. The thickness of the pipe wall varies according to the pipe diameter. The wall thickness of the ½-inch K-tube is 0.049 inches, and the ¾-inch wall thickness is 0.065 inches. Its thickness also makes Type K the heaviest and most expensive copper tube type. You won't find K-type copper pipes under the sink or connected to other plumbing fixtures; partly because they are not as easy to use as other types of copper, but mainly because of the high cost. Type K thickness is suitable for commercial pipes, HVAC, and sprinkler systems, but is most commonly found in groundwater mains installations. Thinner pipes can curl or collapse underground, but the durability of the K type will make it last longer, which means it does not need to be dug every few years.

K-shaped tubes are distinguished by green marks, and there are two types of rigid and flexible rolls. You will often find K-type flexible reels for groundwater mains because they are easier to run in trenches, do not require accessories, and can be used with compression and flaring accessories. The rigid form of the K-tube is more likely to be used in commercial indoor applications and sprinkler systems.

Best for: Groundwater mains. Editor's recommendation: Mueller Streamline K-type copper tube coil (available at Lowe's) is used in underground applications such as water pipes due to its ease of use and durability.

Although not as thick as Type K, the wall thickness of a 3/4-inch diameter pipe is 0.045 inches, but it is still very durable and can be used in more ways. The L type is strong enough for underground applications, but is usually used to replace or repair water pipes. If the house is known to have water problems such as hard water, L-shaped copper pipes are usually the first choice, because hard water will not pass through thicker walls as easily as through M-shaped pipes.

Type L is marked in blue and is used in indoor water supply systems, hot water heating systems, and fire fighting systems (such as sprinkler systems). It is the most commonly used type of copper pipe. It has two types: flexible rollers and rigid pipes. Rigid pipes are usually used for internal water pipes, while flexible rollers are used for underground and outdoor use.

Best for: Most things, but especially internal waterlines. Editor's recommendation: The 10-foot-long Mueller Streamline L-tube (available at Lowe's) is a durable choice for household plumbing installation and maintenance.

For 3/4-inch diameter pipes, the wall thickness of the M-type is 0.032 inches, making it thinner than the K-type and L-type copper pipes. Although this seems to be a point on the "disadvantages" list, it is actually not the case: there is less copper in the M-type copper tube, making it lighter, less rigid, and easier to use. Most importantly, its cost is lower than other copper tube types!

The M type has a red mark and has soft rolls and hard tubes. Although it is not commonly used in outdoor underground applications, if you want to run a water supply system in your home, M-type copper pipe is very suitable and very durable. In fact, its affordable price makes it the most popular copper pipe for domestic water supply systems.

Best for: household water pipes. Editor's recommendation: The relatively low price of Mueller Streamline M copper tubing (available at Lowe's) makes it a popular choice for running household water pipes.

The letters DWV stand for drain, waste, and vent pipes-this helps remind us that DWV pipes are only approved for drain and vent pipes. As the only type of copper tubing not used in water systems, DWV tubing is a bit "strange". The diameter of copper DWV tubes is larger than other types of copper, and they are distinguished by yellow marks. It also has thinner walls than other types of copper pipes. For a 1¼ inch pipe, the wall thickness is 0.040, which is the smallest diameter available for DWV. The thin wall of the DWV copper pipe can only withstand the maximum pressure rating of 15psi, so the application range is very narrow. It often appears in old houses, but if you have a new house, don't bother looking for copper DWV pipes in drains or ventilation ducts. It is almost eliminated in new buildings and replaced by PVC pipes.

Best for: Usually only found in the drainage and ventilation systems of old houses.

Editor's recommendation: Although it is rarely installed now, Cerro copper DWV tubes (available at The Home Depot) are still occasionally used for maintenance work.

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