Sanity check on pipe sizes for new construction

[Nightfall]

I am very early in the process of building a new home. The builder's preferred plumber sub uses CPVC. I'm fine with that, provided it's adequately sized. This evening I checked on some other building sites in progress that serve as examples of what I can expect on my project.

For a house with 35-40 WSFU's, the plumber is using 3/4" CTS CPVC as the main trunk from the 1" water supply / 3/4" water meter. That seemed small, but what really caught my eye was the plumber's use of long, branching runs of 1/2" CTS CPVC.

For example, a single hot/cold pair of 1/2" CPVC lines on the second floor supplies the laundry room plus a bathroom with 2 lavs, a toilet, and a tub/shower. Furthermore, this 1/2" CPVC branch off from the 3/4" CPVC line happens in the basement, so the overall length of the 1/2" CPVC line must be 30+ feet. There are other examples of sizing that I question, such as a hot/cold pair of long 1/2" CPVC lines run from the basement and expected to supply two shower valves that would be operated simultaneously (i.e. a rain + body) plus two lavs and a toilet. All this is allowed by my city's plumbing code that stipulates minimum 1/2" line size for these fixtures, though the code does not address the fact that 1/2" CTS CPVC is roughly equivalent to 3/8" Type M copper.

Based on what I've read on the forum here and elsewhere on the internet, I believe this approach is very inadequate. However, I'm not a plumber myself and I don't want to go off half-cocked with the builder/plumber.

Can I get a sanity check? If I am in fact correct in my belief that this is inadequate, what should I be pushing for in my house with 39 WSFU? E.g. should I ask for 1" CPVC main distribution, with 3/4" CPVC branches to each bathroom, skip it all and go with 3/4" & 1/2" type M copper, or something else?

 

[hj]

Well, the TOTAL WSFU is NOT the important thing. What is material is HOW MANY fixtures will be used simultaneously, but I have NEVER installed even 1/2" copper to supply more than two fixtures off the 3/4", or 1", main. However, if your code and inspectors allow those sizes, you will not get far unless you are willing to pay extra for the upgrade.

 

[Sponsor]

 

[Terry]

If they are using 1/2" for more than two plumbing fixtures, like a shower and a lav, then it's not being done right.
These charts are right out of the UPC code book.

If I'm plumbing for one bathroom, I use a 1/2" hot and a 3/4" cold line.
If I'm running two bathrooms, I doing 3/4" on the hot and the cold.

 

[FullySprinklered]

How many people are using water in your house?

Should you set things up for the maximum for your current situation or for the next joker who owns your house ten years down the road, or should you just take care of yourself in the here and now?

Not a plumber decision, but more a homeowner decision.

This fixer piece of hell that my wife and I are living in has 1/2 in lines going to the water heater and everything else in the house. Everything works fine for the two of us, no problems.

You be the judge when it comes to pipe sizing and total demand, considering your projected demand on a daily basis, or holiday demand when you may have visitors, or the shakiness of your daughter's marriage and the chance that she might come back home to live with a couple of kids.

 

[Nightfall]

Thanks for all the informative replies.

Well, the TOTAL WSFU is NOT the important thing. What is material is HOW MANY fixtures will be used simultaneously, but I have NEVER installed even 1/2" copper to supply more than two fixtures off the 3/4", or 1", main.

That makes sense. I mentioned it because it seems to me that the planned 3/4" CTS CPVC main is equivalent to a 1/2" copper main. I am hoping to learn what sizes I should specify in the plumbing design. To wit, would a 3/4" copper/1" CPVC main typically be sufficient for a 3.5 bath / 39 WSFU home? Given that water size table Terry posted above, it looks like 1" copper would be the minimum.

However, if your code and inspectors allow those sizes, you will not get far unless you are willing to pay extra for the upgrade.

Right. I am not attempting to get a free upgrade from the plumber—I just want adequately sized supply.

If they are using 1/2" for more than two plumbing fixtures, like a shower and a lav, then it's not being done right.

Just to be sure I'm not missing something basic, here's an example from an equivalent project. This pair of 1/2" CPVC lines supplies two lav sinks, a toilet, a tub/shower, and the laundry. The shots here show the first lav & tub/shower, and on the other side of the wall the laundry from the same pair. The 1/2" CPVC lines then wrap around the wall of the room, another 20 feet or so before they feed the toilet & 2nd lav on the other side of the room (not pictured):

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And here, the dual shower & toilet being fed by a pair of 1/2" CPVC lines (lines that also feed two lavs, not pictured):

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If I'm plumbing for one bathroom, I use a 1/2" hot and a 3/4" cold line.
If I'm running two bathrooms, I doing 3/4" on the hot and the cold.

Thank you for elucidating that rule. I would strongly prefer that the project be designed correctly. Excessive flow velocity, noisy pipes, inadequate pressure in demand situations, reduced lifespan of the work, etc, are what I want to avoid. Follow on question: is it typically simpler/less expensive to switch to 3/4" copper as opposed to trying to use the equivalent 1" CPVC size around inside the 2x4 walls that are to be used on most of my house?

This fixer piece of hell that my wife and I are living in has 1/2 in lines going to the water heater and everything else in the house. Everything works fine for the two of us, no problems.

Interesting. That sounds like what this plumber is doing with new construction (3/4" CTS CPVC being roughly equivalent to 1/2" copper)... but then most of the rest of the house is done with 3/8" copper equivalent that is heavily branched.

 

[Nightfall]

Talked to the plumber in question. He informed me that local code allows 9 WSFU on a single 1/2" CPVC line; therefore, it works "perfectly well" to have a washer, toilet, two lavs, and a tub/shower served by a 30+ foot, 1/2" CPVC line. Apparently local code spec for WSFU differs (e.g. it counts a tub/shower as 2), which is how the above adds up to less than 9.

He also told me that upsizing the pipes for this by one step (i.e. 1/2" => 3/4") would be a "terrible idea" and it would take "forever" for hot water to arrive. I was told he went to school for five years to do this job, that he knows how to calculate these things, has hundreds of equivalent installs from satisfied customers, etc. He then offered to sell me copper instead for an extra $2500 or so.

 

[Bluebinky]

Not a pro, but IMHO, at least the toilet should have its own supply and the washer its own too. There is truth to his logic on the hot side, but his "design" sounds cheap and inferior. The code is a minimum, not necessarily the ideal.

 

[Jadnashua]

Here's one manufacturer of CPVC's thoughts on sizing cpvc systems...

http://www.pssurvival.com/PS/Hydro-Power/Frictional_Losses_At_Different_Flow_Rates_PVC_Pipe_2007.pdf

They call for a maximum velocity of 10fps, the same for hot or cold (that differs from the recommendation on copper - it's higher). You'd need to know the ID of the pipe to determine if you were going to exceed that velocity. If it does, especially if it is way in excess, I think you'll have a leg to stand on, as often the code relies on manufacturer's instructions as part of the approval on installation.

I've done the calcs on 1/2" copper, and at 10fps, that comes out to about 8gpm. CPVC has a smaller ID, so it would have less volume at the same velocity.

 

[Terry]

He also told me that upsizing the pipes for this by one step (i.e. 1/2" => 3/4") would be a "terrible idea" and it would take "forever" for hot water to arrive.

If he feels that way he can manifold the plumbing to speed things up and still maintain flow when everything is being used.
The repipe I did last week of a 60's home was three 1/2" lines to the West side of the home to feed three bathrooms. Each bathroom had it's own 1/2" line.
To the East, I had a forth 1/2" line feeding the kitchen and washer.

Nebraska uses the same UPC book I do, but their local inspectors are not the same as ours.
The plumbing you showed above would never fly here.

 

[FullySprinklered]

Three fixtures on a 1/2 in pipe is the rule I grew up with.

 

[Jadnashua]

IMHO, it really depends on what that line is supplying and how long it is plus, how much of a pressure drop you are willing to live with. This is backed up by all of the charts as well. Many people will not be happy with simultaneous use of devices on a single 1/2" line. The way it usually works in a bathroom is you're not using all of the devices at the same time...but, someone sharing it, flushing a toilet and then washing their hands while you're taking a shower and you WILL notice! Well, they'll notice at the sink as well.

 

[Nightfall]

Thanks again for all the replies.

Many people will not be happy with simultaneous use of devices on a single 1/2" line.

Yes. I guarantee you that the washer will be running at the same time someone is taking a shower. Someone may even be flushing the toilet & using the lav. These simply cannot all be on same lengthy 1/2" CPVC branch.

If he feels that way he can manifold the plumbing to speed things up and still maintain flow when everything is being used.
The repipe I did last week of a 60's home was three 1/2" lines to the West side of the home to feed three bathrooms. Each bathroom had it's own 1/2" line.
To the East, I had a forth 1/2" line feeding the kitchen and washer.

Thanks. What you described seems intuitive.