Series piping vs Parallel piping

[DavidTu]

I asked about two plumbing designs with a long post and PDF diagrams, and no one responded. Let me try a simpler approach and ask the experts to characterize the effect of running pipe in series vs parallel.

In other words, comparing the idea on one hand of a giant hot water loop through a house feeding all the fixtures compared to serving the same fixtures by "zone-runs" which can be thought of as running larger homeruns to various clusters of fixtures from where they are then distributed to individual fixtures. If our main concern is not losing pressure or temperature in showers while other things like washers or dishwashers or kitchen sink are running, which system will work better?

Now let's add one more wrinkle: recirculation. On the one hand the loop design is ready-made for it requiring returning to the hot water heater, a pump, and a check-valve. The zones-run design is necessarily more complex so how would that best be implemented and how well would it work in comparison? (My original post--see below--had a proposal for it if you just want to weigh in on a proposal rather than make one.)

(If you want the details, please look at my original post--you can mostly look at the PDFs and only read the post to clarify what you're looking at if you need it. Here is the link.)

 

[wwhitney]

If our main concern is not losing pressure or temperature in showers while other things like washers or dishwashers or kitchen sink are running, which system will work better?

For this question, definitely the parallel runs. Any portion of shared piping between the flow going to two different fixtures will allow the draw from one fixture to affect the pressure available at the other fixture. So for the "not losing pressure" part, you want to minimize the shared piping.

Of course, I doubt that is really your only criterion. There's also wait time for hot water after you open the tap. There recirculating will win, and it's much easier to implement with a loop.

Then there's also energy usage. I think for this the parallel runs probably win, as each usage minimizes the amount of pipe that gets left with stale hot water after usage, which represents energy used to heat water but never delivered as hot water. That's for sporadic usage; for certain unlikely usage patterns, the loop would be better (say you use each fixture in the loop, one after each other; then you only pay the energy cost of stale water at the end of the usage pattern).

Then there's also water usage. For this, recirculating will win, which is easier with a loop. No water down the drain waiting for it to get hot.

One thing that wins with either is designing your house so that all the hot water usage is clustered spatially, thereby reducing the total amount of hot water piping. Generally only possible in new construction or a serious gut remodel.

Cheers, Wayne

 

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[John Gayewski]

Run the single loop for hot water. Unless your piping is extremely undersized your not going to loose pressure or volume with a single loop. The amount of components and piping you'll need for parallel runs is ridiculous.

Don't include a clothes washer in the loop as it doesn't need instant hot water.