It is essential to be familiar with how to choose water lines for your construction project. There are many types available in the market, from traditional copper pipe to modern pex pipe. Despite the material, size is also an important feature to consider. How would you know which one works best for you?
This blog post will cover a basic introduction to PEX water pipe sizing and provide a simple guide on how to size the water line for your project, including calculating total fixture numbers, etc. If you are looking to transfer from copper pipe to pex, learn more at PlumbingSell.
Table of Contents
Sizing of the pex water pipe
PEX piping is flexible, durable, and corrosion-resistant that has been widely used in plumbing systems. PEX pipes come in various sizes, typically ranging from 3/8-inch to 2 inches. For residential usage, the most common sizes of PEX pies are 3/8-inch, 1/2-inch, 3/4-inch, and 1-inch. It’s important to note that, unlike other types of pipes, PEX pipes are not measured by their internal diameter. Instead, they are sized according to nominal size, and their actual internal diameter could be smaller due to the thickness of the material.
Please find attached sample dimensional data and specifications for the mostly used residential PEX pipes.
We recommend using 1/2-inch or 3/4-inch PEX for plumbing systems that only require adequate water flow. To be more specific, 1/2-inch pipe is mainly used to connect fixtures, while 3/4-inch performs better as the main supply line in moderate-sized residential projects.
The length of PEX tubing varies from 50-foot to more than 500-foot rolls. With the pex pipe crimping tool, you can simply connect two pipes together. For instance, if you are doing a minor repair, you could use the tool to connect the pex pipe with the existing one.
How to size the pex water lines
Before we dive deeper into understanding specific pex pipe types like 3 4 pex pipe, it’s important to at least know how to size the pex water lines. Not only the diameter of pipes required or the length you required but also the distance between each fixture as well as the distance among them. Properly sizing water lines is essential for adequate water flow, pressure, and efficiency in any plumbing system. The factors that influence the size of water lines consist of fixture demands, pipe length, pressure loss, and local plumbing codes. Below is a detailed explanation of the main factors that will help you determine the proper pex pipe size for your application.
Calculating Total Water Supply Fixture Units (WSFU’s)
We are going to start the process by calculating the total number of fixture units required. This is basically how many fixtures you want on the water system in your application. Examples of common fixtures in residential and commercial constructions include toilets, sinks, bathtubs, showers, dishwashers, and washing machines.
Each fixture is assigned a Water Supply Fixture Unit (WSFU) value on how much demand it requires. This is a unit used to measure the flow rate of water through a specific fixture. The WSFU can be found in the plumbing code of the pipe you use accordingly.
Total Developed Length of Piping
The next step is to calculate the developed length from the farthest fixture to your water meter. In other words, it is the distance between the water source and the most remote fixture. The easiest way to measure this is by tracing back along the center lines of the pipes until you reach the water meter. However, do keep in mind that fittings and valves add a certain amount to your total length, which mainly depends on the water system design.
Calculating friction losses through every fitting and valve can take a lot of effort and time, especially for complicated water systems that involve multiple types of fixtures. A good rule to follow is to leave an extra 15% to 50% of the overall piping distance. For example, a standard project with minimal changes in direction could need a 15% additional length. In comparison, a complicated commercial building that involves a large amount of fittings and changes in direction may require up to 50% extra piping distance.
Even though it is always good to leave some space for justifications, remember that the longer the pex pipe runs, the more pressure will be lost due to friction. Also, if the pipe is too small, water pressure at further fixtures will be too low.
How to Calculate Water Pressure & Causes of Pressure Drop
There are generally two types of water pressure in the plumbing system you need to consider. The first one is static pressure, which is the pressure of a fluid at rest. In other words, static pressure is measured when there is no fluid movement. The other one is dynamic pressure, which is measured when fluid flows through the pipes.
To calculate the water pressure in your lines, the main factor you will need is the elevation of the highest fixture. Suppose the highest fixture in your application is above the meter. In that case, a loss in pressure will happen, and this refers to a 0.5 PSI (pounds per square inch) pressure loss for every foot of elevation gain. In contrast, if the highest fixture is below your meter, you will add 0.5 PSI for every foot of elevation drop.
The definition of pressure drop is the pressure lost when water flows through a pipe. Several things could cause this pressure loss. Factors such as pipe size, material, length, and the number of fittings and fixtures attached to it could all cause potential water pressure drops.
PEX pipes typically perform best between 40 and 60 PSI. If the incoming pressure is lower than this amount, you may need a larger pipe to compensate. For example, if the water pressure is 30-40 PSI, then you could use 3/4″ pex pipe instead of 1/2″ pex pipe.
3/4″ pex pipe
In residential plumbing, 3/4-inch pex pipes are widely used as the main water line. This size is considered the standard for many types of residential water supply systems, as it is large enough to handle water flow for standard fixtures while remaining compact.
Now let’s use a 3/4″ pex pipe as an example of discussing the number of fixtures you can put on the home water supply. As we mentioned before, when designing a plumbing system, the calculation of total water supply fixture units (WSFU) is required. However, in reality, very few fixtures draw water at the exact same time. Therefore, the question is not actually how many fixtures you supply; rather, it should be how many fixtures you can supply simultaneously on one water line.
In general, the number of fixtures that the 3/4″ pex pipe supplies mainly depends on factors like water pressure, pipe material, and local plumbing code. If you have more fixtures, then the water flow rate in the main supply line should be increased. For projects that require larger water pressure, you might need to extend the existing pipes; we’ve got plenty of pipe fitting options to help; check out the 3/4″ pex pipe fittings prices here.
Conclusion
We hope we’ve helped you with the introduction to PEX water pipe sizing and guided you to choose the size of the water line for your project. With the methods for calculating the total fixture units, you should now be able to decide the proper sizing of pipes to use. To sum up, we want to remind you to always consider the possible factors that impact water pressure. For instance, the number of fixtures on a 3/4″ pex pipe is not limited to any number as long as the water pressure is consistent. If you need further information, don’t hesitate to reach out to us. Check out more details about PEX pies here.
