Does Using PEX Reduce Water Pressure?

PEX plumbing has taken the plumbing world by storm in the past few years, commanding the attention of many (but particularly DIYers). After all, the material is cheap, flexible, and easy to install, so why wouldn’t you choose PEX over a rigid material?

While PEX certainly has its perks, it’s essential to understand the specifics before implementing it into your plumbing system.

Key Points:

  • PEX plumbing is a cheaper, more flexible material than rigid alternatives and can be used in DIY plumbing projects.
  • Fittings installed in the tubing can result in pressure drops of 2 to 4psi per 90° elbow fittings.
  • When switching to PEX, it’s possible that water pressure might drop; however, upsizing the tubing may help prevent this.

When outfitting a plumbing system with PEX, it’s essential to understand the potential for significant drops in water pressure. This article explains water pressure drops when using PEX and whether that affects the usability of the material, so continue reading to learn more!

What Is PEX?

Cross-linked polyethylene, better known as PEX, is a popular flexible tubing commonly used for plumbing and radiant heat applications. Since the material is flexible, it’s much easier to work with than alternative plumbing materials, like copper or PVC, which are rigid. Installers can easily manipulate the tubing around corners, skipping the need for joints altogether.

This makes it an ideal option for DIY plumbing tasks, as installers don’t need to worry about soldering joints or installing a complex plumbing setup. Since the tubing is flexible, it isn’t prone to bursting, as it can expand slightly if freezing occurs.

On top of its DIY-friendly and flexible nature, the material is inexpensive and widely available at most home improvement stores. Although it doesn’t last quite as long as copper, which can last a lifetime, it can hold up well for 50 years or more.

Does PEX Tubing Affect Water Pressure?

Although PEX tubing can be an excellent alternative to other piping materials, it can affect the water pressure throughout your plumbing system. Unlike other plumbing materials, which often use joints fitted over the pipe, PEX tubing requires fitting inserts.

The inserts are necessary to ensure the tubing doesn’t collapse under the fitting as you install it using special tools (crimp tools, expansion tools, etc.). Since they sit inside the tubing, they detract from the total internal diameter of the pipe at each fitting. They can impact the flow and water pressure, dropping it slightly.

Of course, the drop varies based on the type of fitting you use, as some are better than others. In many cases, the internal diameter of a ½-inch PEX pipe drops by 21% to 35% with varying fittings. The diameter change makes up for a drop of two to four psi at each 90-degree elbow fitting installed throughout the system.

The exact pressure drop varies based on the fitting you use, as some create smaller drops, while others may cause significant pressure drops. PEX fittings come in varying types, including crimp fittings, expansion fittings, and push-fit fittings.

Although some manufacturers boast that the tubing and fittings don’t reduce the water pressure, this is often untrue. Customers can usually find information surrounding pressure drops and equivalent lengths in data provided by the PEX manufacturer, which can aid in determining whether PEX is a good fit for varying projects.

Do You Lose Water Pressure Going From Copper To PEX?

When switching from copper piping to PEX, it’s entirely possible that you’ll notice a pressure drop. However, to combat the issue, you can upsize the PEX tubing to ensure proper water pressure throughout the system. Before switching to a larger system, though, calculate the system’s needs, as it’s not always necessary.

For example, let’s take a look at urinal plumbing. According to the International Plumbing Code, a urinal must have a flow pressure of 12 GPM (gallons per minute) at 25 psi (pounds per square inch). If you outfit the system with copping piping, the figures look like this:

  • 65 feet of 1-inch copper L pipe
  • 5 1-inch copper 90-degree elbows for 2 ½ feet per elbow
    • The complete pipe length is 77 ½ feet of pipe (2.5 x 5 = 12.5’ + 65’ = 77 ½)
  • 1-inch copper pipe at 15 GPM with 0.057 psi loss per foot
    • Total loss of 4.4 psi (77 ½ x 0.057)

Conversely, the setup for PEX looks a bit different:

  • 65 feet of 1-inch PEX tubing
  • 5 1-inch PEX 90-degree elbows for 10 feet per elbow
    • The total tubing length is 115 feet (10 x 5 = 50 feet)
  • 1-inch PEX at 15 GPM with 0.132 psi loss per foot
    • Total loss of 15.2 psi (115 x 0.132)

There is a noticeable pressure drop from PEX to copper. While the copper system has a minimal pressure loss of 4.4 psi, the PEX system has a total pressure loss of 15.2 psi. In this particular scenario, upsizing wouldn’t be necessary, even though PEX delivers a noticeable pressure reduction.

The reasoning behind this stems from the requirements of the system. Let’s say you’re starting with an available pressure of 65 psi. With a copper system, you’d end up with 60.6 psi due to the drop, but with a PEX system, it would deliver 49.8 psi.

Although this is a noticeable drop, the system still delivers plenty of pressure to accommodate the International Plumbing Code’s requirements for urinals. On top of that, you could minimize pressure drops in the PEX system by using bend supports instead of elbows, which would lower the pressure loss in the PEX system to 4.2 psi, which is nearly identical to the copper system’s pressure loss.

So, while the pressure drop with PEX is nearly inevitable, it’s not always a game changer. Sometimes, you can simply change the approach, like using bend supports instead of elbows, to correct the issue. Or, you might not even need to make adjustments based on the plumbing requirements of the fixture you’re working with. It all depends on the situation.

How Do I Know If PEX Will Work For My Project?

Given the undeniable pressure drops from many piping materials to PEX, there might be better choices for some situations. While you can upsize the tubing to skirt these reductions, determining the ideal size can be tricky.

We recommend using the PEX manufacturer’s data surrounding pressure drops and the factors specific to your project (pressure requirements, flow rates, design velocity, etc.) to determine whether the tubing is a good fit for the project. This information can be extremely helpful in assessing the viability of PEX for your plumbing project.

However, if you’re unsure how to apply this information or determine whether PEX is a good option, we recommend discussing the topic with your plumber. They can evaluate the situation using factors specific to your house or building, as every case is different, so the advice isn’t always a one-size-fits-all thing! Then, they can use this information to help you determine the best path moving forward.

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