How to Design a PEX Water Manifold

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Once you’ve determined you want to go all in on a PEX water manifold, a proper design is essential to high performing plumbing system. You have one shot at doing this right the first time so let’s set you up for success!

Laying out the Plan:

1. First, you want to decide if you want a full home run to each faucet / outlet, or if it will be a semi-trunk and branch / manifold combination. The benefits of a full on manifold with only home runs are clear, but you need to determine if the initial cost is worth all the future benefits such as detecting hard to find leaks, servicing any faucet / endpoint at the your convenience (along with other advantages listed here: Advantages of a Plumbing Manifold System). We think it is…
2. Compile a list of all the hot and cold lines you want to run in this house. A list of potential endpoints are listed at the end of this post.*
3. Plan for future expansion. Better now while the walls are open then later when is is infinitely more difficult to expand. Just run a line to the ceiling and cap it off.*
4. What size PEX manifold do you need? It depends on your two answers to the previous two points.
5. Consider how you use your hose bibbs outside as well as if you plan on having a salt water system. Is there an irrigation system in place that splits off before the manifold? You don’t want to pour salt water on your plants constantly. Depending on your answer, you may need to place the hose bibb PEX lines before the manifold.
6. Consider the demand on each outlet / how much water pressure desired at each outlet. Size the outgoing line of PEX coming out from the manifold accordingly. For instance, the faucets are all coming off ½” connections and PEX line. Hose bibbs are ¾” to keep up with manual watering or car washing water pressure demand.
7. Where are you planning on installing the manifold? Is it in a central location so the master shower is not waiting five minutes for hot water to arrive? Is the house large enough to warrant two water heaters and two PEX water manifolds?
8. Also consider the distance from the water heater to the hot water manifold. The longer the distance the more cooling takes place before it gets a chance to make the longest hot water run.
9. Do not forget to include a drain spigot at the bottom of both the hot and cold water manifolds.

An Example PEX Water Manifold Design:

We’ve been asked a couple times to diagram the outlets in the PEX water manifold we shared here: How to Build a Whole House Uponor PEX-a Manifold.

This house has a manifold cabinet with both the hot and cold water lines housed together on an interior wet wall of the house. Each PEX line is a home run to a faucet . How we designed it–and influence how you want to design your own–is best discussed by looking at the installed manifold itself.

Here is the PEX water manifold with each outlet labelled:

Here is a diagram for how we would design the same plumbing manifold if we did it again. This includes one of the biggest lessons learned here in this post: Sanity Saving PEX Manifold Installation Tips.

The main difference is the location of the drainage spigots. They should be within the confines of the manifold cabinet. It is also ideal to have them at the bottom of each manifold. This location at the bottom ensures the spigot fully drains the entire manifold when opened.

Other issues that will make a difference in your own design:

1. Notice there are two lines (one on each side) for future expansion. Again, these are prerun to the ceiling and capped.
2. We do wish it was possible to move this manifold to a more centralized location. As this is a remodel and the house is designed the way it is, this PEX water manifold is on one side of the house. Thankfully, it is close to the higher demands of kitchen and laundry life, but it is not ideal for the bathrooms on the other side of the house.

Again, check out this post here to make your own PEX water manifold design and plumbing layout easier and more efficient: Sanity Saving PEX Manifold Installation Tips

Still on the fence about a water manifold? Check out this post for more reasons: Advantages of a Plumbing Manifold System

General FAQ

What size PEX manifold do I need?

Compile a list of all the hot and cold lines required in your home. Next, consider future expansion and decide how many additional lines should be included to run a line of PEX to the ceiling and cap them off. These two answers will give you the proper size manifold.

What is the best place for a water manifold?

As close to the middle of the house as possible. The line from the water heater to the hot water manifold should be as short as possible too. If there is too much distance consider installing a second manifold and water heater.

What size PEX should I use?

3/8″ to 1″ is acceptable for residential use. Consider the demand, distance, and how much water pressure desired at each outlet. Larger PEX equals more pressure. For instance, the faucets generally use 1/2″ PEX. Hose bibbs are larger (the PEX manifold photographed is 3/4″) to keep up with manual watering or car washing water pressure demand.

*Here is a list of possible lines you need to include in your manifold plumbing system design–you don’t want anything to get accidentally missed:

Kitchen sink
Dishwasher
Refrigerator Ice/Water Line
Dedicated ice maker
Pot filler
Bathroom sink
Bar sink
Toilet
Shower
Bathtub
Washing Machine
Water Heater
Water Softener

Consider these with care if you plan / ever even slightly consider adding a water softener:

Outside Spigots
Outside Kitchen Sink
Utility Sink
Pool
Sprinkler System