What Is the Difference Between L and M Copper Pipe

I’ve been learning about the copper pipes in my home because I’ve been doing some remodeling. Based on my research, I thought I’d put together this article to explain the difference.

The difference between L and M copper pipes is that L copper pipes are thicker than M copper pipes. L copper pipes last longer than M copper pipes when used to supply water throughout a house or building. L copper pipes are more expensive than M copper pipes, and for that reason, M copper pipes are sometimes preferred.

In this article, I will cover everything you need to know about the differences between the four types of copper pipes, when you should use each type of copper pipe, and how to know whether you should use L or M copper pipes.

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Should I Use Type L or Type M Copper Pipe?

The difference between type L and type M copper pipes is that type L pipes are thicker. However, when should you use type L copper pipes, and when should you use type M copper pipes?

As a general rule, you should use type L copper pipes for water supply in a building. Type M copper pipes are acceptable in most jurisdictions (but not all) for water supply. However, type L copper pipes last longer because it's thicker and won’t need to be replaced as soon as type M copper pipes.

Most plumbers recommend using type M copper pipes for the supply of heating, such as in an underfloor heating system. However, type M copper pipes are a lot cheaper than type L pipes.

Type L pipes contain more copper because it’s thicker, and as a result, they cost more. Thus, some people use type M pipes instead of Type L copper pipes to save costs. However, Type M pipes will need to be replaced sooner than type L pipes.

In a recent article, I explained when copper pipes need to be replaced. You can read it [here, link how long t]. And copper pipes generally will last 80 to 100 years. But, some plumbers believe that if you use the thinner type M pipes instead of type L copper pipes, you will need to replace them after 20 to 30 years. 

Some jurisdictions require Type L pipes

Across the board, internationally, you can use type L or type M copper pipes for supplying water throughout a house. However, in certain jurisdictions, you can find that they require type L pipes to be used.

Water pressure is the primary cause because some municipal water sources require high water pressure to meet the demand. The thicker L copper pipes can withstand higher pressure than the M copper pipes. Therefore, before you buy them, it’s best to talk to a local plumber in your specific area or access the building codes on your local government website.

It can often be challenging to find the specific information, so it’s often easier to contact a plumber via phone or email. But it’s your responsibility whether your project meets your local building codes. And if it’s incorrect, you will need to foot the bill to replace them.

Therefore, it’s a good idea to make sure it’s all above board before installing or replacing copper pipes.

What Are the Different Types of Copper Piping?

There are a few different kinds of copper piping, and they can be identified by the color of the lettering used on the outside. I’m interested in what each of the different types of copper piping is used for. Here’s what I found.

There are four types of copper pipes, K, L, M, and DMV. K copper pipes are the only type of copper pipes that can be buried underground. L copper pipes are used for supplying water, whereas M copper pipes are used for heating. DMV pipes aren’t used for water supply and have no pressure rating. 

DMV pipes are generally only found in old homes and have been phased out because plastic pipes are cheaper and easier to work with than copper piping. And M copper pipes CAN be used for both water supply and heating supply. 

Here’s a table that shows how to tell the different kinds of copper piping apart, and what they’re used for:

Type of pipe and color codeUsed for
K – greenThe only type of pipe that can be buried underground. Used for water supply into a building.
L – blueLocated inside a building and used for supplying water throughout the building.
M – redRecommended to be used for heating systems. It can be used  for water supply lines but not recommended
DMV – yellowUsed for drainage and vents. Not widely used much anymore, and typically only found in old buildings.

There will be a thin strip of color and/or lettering on the outside of copper pipes to indicate what kind of pipe it is. For example, L copper pipes will have blue lettering or a thin strip of blue paint.

Thickness of the pipe and the pressure rating

Water flows through pipes under pressure. And for water to get from the ground to a shower head, or an upstairs kitchen or bathroom, it needs to be pumped under reasonably high pressure.

Each type of copper pipe has been stress tested in a lab to see how it holds up under varying water pressure. 

But, pipes have a diameter and a thickness – which can be a bit confusing because a large pipe can have thin walls, and as a result, can withstand less pressure.

As a general rule, the thicker the pipe – not the diameter of the pipe – means that you can use it for water that’s under higher pressure than thinner copper pipes. And pipes with thicker walls will last longer than pipes with thinner walls under the same conditions.

Which Copper Is Thicker L or M?

A major difference between the types of copper pipes is how thick they are. And therefore, how does the thickness of L and M pipes compare?

On the whole, type L pipes are thicker than type M pipes. L and M copper pipes commonly are ½ an inch (12.5 mm) or ¾ inch (19 mm) in diameter. The thickness of ½ inch L copper pipes is around 0.032 inches (0.8 mm). The thickness of ½ inch M copper pipes is around 0.045 inches (1.1 mm).

As you can see, the difference in the thickness between L and M copper pipes is only minimal. However, because L-type copper pipes will last longer, they can contain water at higher pressures. Which results in less wear and tear on the pipes.

Copper, though, is relatively rare and costly to extract from the ground, and for that reason, type L pipes are more costly than type M pipes because they contain more copper and are on average around 15% of the price of type L pipes.

Here’s an average cost comparison between type L and type M copper pipes:

Type of copper pipeCost per 10 ft (3 meters)
L~$125 (1 inch)
M ~$25 (3/4 inch)
*Price as of 2021, according to Lowe’s Home Improvement store. Price varies by location and supply.

Because of the drastic difference in price, where possible M type copper pipes are used rather than type L, however, type L is recommended by plumbers because it lasts 3 to 4 times as long as type M copper pipes before they need to be replaced.

Sources

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Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.

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