# Should a water distribution manifold consist of a circular loop?

I'm replacing the copper in my house with PEX tubing and I'd like to set up my new utility room with hot water and cold water manifolds. Each connection on the manifold would then lead to either hot or cold on a plumbing fixture and I'd have shutoff valves to each at the manifold.

I recalled hearing somewhere that each manifold should consist of a circular loop; that is, the manifold should not terminate directly, but should contain a connection to circulate water back to the inflow of the manifold. I'm not sure why this should happen, or if it should happen.

Don't know whether it matters, but I'm on well water.

• Well water does not matter – Jack Jan 28 '14 at 15:41

The circular loop would only be for the hot water side. It is called a recirculating line and it is in place so when you turn the hot water on the line will not have to purge the cold water first, the hot water will be there at the ready in seconds. It is more expensive in energy costs since the hot water is always moving through the pipes and loosing a little heat which would need to be maintained.

• Absolutely correct. Loop hot water is normally used in commercial where there are frequent calls for hot water. It is very expensive to use this method for normal residential usage. – shirlock homes Jan 28 '14 at 21:15
• In my years of working for a company as a supervisor that did high end homes, there were many installed in that situation too, LARGE single family homes. – Jack Jan 28 '14 at 22:29
• Agree with you Jack. High end homes with lots of \$\$\$ use it all the time. – shirlock homes Jan 28 '14 at 22:56

A circular manifold is not a hot water recirculating loop, though a hot water recirculating loop could conceivably be set up as a sort of large ring manifold. It is simply a manifold arranged as a ring, typically only a few feet in diameter and located near the water supply, and it provides a couple of advantages, depending on exactly how it's built. The main advantage is that it effectively doubles the pipe area of the manifold - water can flow both directions from the input to any load, and this is particularly helpful when multiple loads are drawing at the same time; this is as compared to a linear manifold where the last item on the manifold will see less pressure when other items "before" it in the manifold are drawing. There is also a large cost advantage over pre-built manifolds, but that is not specific to ring manifolds.

Of course, there is still a worst location (the side of the ring opposite the input) but it's roughly twice as good as a linear arrangement. If you incorporate valves in the manifold (as well as the valves on the branches) you can isolate a part of the manifold without shutting down water to the entire building. Whether that is worth doing is somewhat debatable.

Arguably, a hot water recirculation loop is not the same as a ring manifold, becasue the nature of a manifold is to try to minimize pressure differences between branches, by having a large, short, tube with all the smaller branch tubes connected to it, all seeing similar source pressure. A recirculating loop running throughout the house would have significant pressure drops between draw points. A system following the manifold approach with recirculating loops would have a loop return from each hot water branch, unless it was using the (IMHO terrible) practice of returning along the cold tube.

A circular manifold provides a "parallel circuit" of water distribution and evens out the water pressure better than a straight line manifold with a "dead-end". See James Glass's video at: