Noobie with question on system design...

Hello All,

Forgive my new post, but 'search' didn't turn up much. Yet. Here's the story:

1922 bungalow needs all new plumbing. Existing is galvanized. Plumber recommends NIBCO PEX and Viega fittings. Do I need Ox-barrier PEX? Pex-Al-Pex? Pex-Al-Pex is probably not necessary since it'll all be underhouse/interior, but does it have other advantages over Pex? Flexibility is not a HUGE issue since crawl space is okay. Longevity is key: I don't intend to do this again, and I plan on being carried out of this house.

City water is very hard: calcium builds up rapidly on Cu pipe, hence the selection of Pex.

I'm planning a manifold system, which seems pretty straightforward. But I have questions about pipe sizing into locations with multiple outlets, such as a bath. To save y'all the hassle of a zillion questions, is there a good source somewhere for such info?

Thanks in advance!

chris

In the past I have used regular pex for water.. I am doing a radiant floor project now and for the floor they sold me pex-al-pex. However I think that mas more to do with the fact that pex al pex is air/gas tight. You want that when you are recirculating the same water.


But for regular potable water I just use regular pex.

when using a manafold I do all home runs.. 3/8 toilets and bath sinks. 1/2" for showers, and hose bibs.

Thanks Zhomes! Okay, I'm with you on the PEX, that's pretty much the answer(s) I expected.

Now on the runs: so if you have a bath (tub, lav, wc) you run three CW and two HW runs from your manifold, even if it's pretty far away? Does that eliminate getting scalded or frozen in the shower if someone flushes?

I was thinking you'd run one supply, say 3/4", then manifold it to the fixtures, but if your way is better I'm okay with it. It'll use more tubing (and less fittings), but if it works better that's what I'll do!

Obviously 3/8 is a typo: must be 3/4".

Thanks again. I'm sure I'll have more questions...

c.

Your shower requires a scald protection valve, so freezing shouldn't be a problem, but pressure variations can be a pain. WIth the new valves, if that were a factor, it would shut down both hot and cold to keep the relative temperature set, and may actually shut off both to prevent a major change in temp. Personally, I like the temperature controlled valve which also means you may only need to turn on the volume control (note, typical pressure balanced valves do NOT have a volume control, it is either on full, or off).

Running pex and off of a manifold minimizes pressure changes assuming you have decent volume capacity to the house.

Do you know what your water main line is? Has that been changed, or is it galvanized, too? It may be time for a new main line and meter as well.

Thanks Jim!
The main was replaced when my garage/studio was built, so it's all good. Right now I have all the house water supply running through a filter system: two 20" canisters, one sediment, one charcoal. The charcoal filter has something like 8 gpm capacity, but I didn't notice any reduction in flow when I installed them, even though they only have 3/4" fittings. Our water is HARD and gritty, and the filters have made a noticeable difference. Eventually I'm going to add another bath, so I'll have to either double up or take them out. But that's another project...

Scald-wise, I just had an instant-on water heater installed, and it's set to 110 degrees. The problem is, after maybe three minutes in the shower, the water turns cold, then eventually cycles back to hot again. I suspect the plumbing, not the heater though. It's such a mess under there, I'm wondering if it's somehow siphoning cold water into the shower's hot side, which would screw up the heater's regulatory system (and freeze my nekkid butt.) It takes a pretty long time to get any hot water anyway, which I'm sure is a result of the old point-to-point plumbing. It would need replacing regardless though: it's probably twenty years past its normal lifespan!

c.

the advantage of running the home runs in 3/8" pex(for sinks), 1/2" for showers/tubs is time to deliver the hot water. I have another post on here where I did some calculations for the time it would hot water to get to a bathroom I was putting in.

I am doing a multihead shower that could benifit from a 3/4" feed.

that 3/4" feed holds a lot more water then a 3/8" feed. you can find my old thread or do pie*r*squared and figure it out youself. the thinner pipe for the home run gets your hot water there faster.

the home runds also saves on the shutoffs... If you you went and did a pex run that hits mutitple fixtures you would then want to terminate each fixtures with a copper stub out and regular shut offs.. that is what my plumber did when he set up a mutlifamily for me. He didnt use a manafold, but branched the pex instead and then put shutoffs at the ends.. the town is just starting to accept pex and I think this was their babystep way of getting there.

I hadn't even considered 3/8" tubing: I just assumed it was too small to meet code. I'll check it out: it makes more sense than 1/2", particularly on the HW side. I'd be happy to run a bunch of little lines: like you said, it'll make a HUGE difference in how fast I get hot water!

Even if I use 3/8" where allowable, I'll probably still have better flow than I do now, what with the number of elbows and tees, and the amount of deposits in the galvanized. It's gotta be at least half-clogged with 'pre-limestone': you shoulda seen what came out of the old water heater!

c.

A tankless heater could be cycling. It requires a certain minimum volume to turn on. Depending on where you live, the incoming water could be a factor in how much hot water you get, too. 110-degrees may be too low, depending on how long the run is. It means that you are using probably 100% hot. You'll get a little more control if you run it a little hotter, and mix some cold in. In fact, you may want to have a tempering valve installed and run it even hotter, letting the tempering valve bring it down to a safe value. 119-120 is probably better, and your dishwasher would love even more otherwise, if it has this feature, it will have to use electric resistance heat elements to heat the water, or your quality will suffer in the wash.

What volume is the tankless supposed to support? Where do you live? What's the incoming water temperature?

Keep in mind that with a tankless, the temperature changes with the volume used, so an anti-scald valve may not do much for you. Even a temperature controlled valve wouldn't do much, since you're normally running the hot full blast.