# 3/8" PEX distribution lines?



## Indweller (Mar 12, 2009)

Thinking about trying PEX. The NAHB and Manabloc install manual advocate 3/8" distribution lines for most fixtures (up to 2.5 GPM), but this diameter seems pretty small. Makes me nervous. Anyone with real world experience install 3/8" lines? Do they work as advertised? How about over time?


----------



## user823 (Feb 3, 2009)

The 3/8" is the fixture supply which is the way it's always been. The building branches would be a minimum of 1/2". Water pipe is sized as per fixture units according to your code book. You have read your code book right? You are a plumber right? Pex is sized the same as copper.
How about an introduction now? What state, how long have you been a plumber etc.?


----------



## uaplumber (Jun 16, 2008)

Yup, an introduction helps alot.


----------



## nhmaster3015 (Aug 5, 2008)

I think he's talking about using 3/8 off the manablock to each fixture. This type system gained some popularity with polybutlyne pipe, probably 20 years ago. Sizing was pretty much non existant, you simply ran a 3/8 feed to every fixture. It had it's advantages (fast, cheap, easy) and it's disadvantages (poor volume and long hot runs took forever) Don't run into it much anymore though for something like a camp it might be a good plan.


----------



## Scott K (Oct 12, 2008)

I would run 1/2" pex. It's more common.


----------



## Ron (Jun 12, 2008)

Stay away from te 3/8 pex off a manifold, for one thing, yes I have encountered the 3/8 as the main lines out to the fixtures, it was quest pipe, if you know what it's like to fix a leak on 3/8 in the wall and almost no way to make the transition from it to pex, almost impossible, supply house will have no way to help you in the case, I did not warranty my repair on it, I had to use a 3/8 comp x 1/2 comp quest coupling. 

Just don't use this crap. I have only found it twice here and once in the walls, no way to replace a run unless you take it all the way back to the block, this was not an option. 

It was not an older house.


----------



## user823 (Feb 3, 2009)

Wouldn't matter here, it's illegal. Minimum 1/2" in walls. Minimum 1/2" branch, 3/8" only allowed as a fixture supply from angle stops. I've never seen a 3/8" branch, didn't know they even existed.


----------



## smellslike$tome (Jun 16, 2008)

ironranger said:


> Wouldn't matter here, it's illegal. Minimum 1/2" in walls. Minimum 1/2" branch, 3/8" only allowed as a fixture supply from angle stops. I've never seen a 3/8" branch, didn't know they even existed.


I routinely come across older houses here with 1/2" copper or galvanized water services and in houses that are all copper I often find 3/8" branches going to everything.


----------



## plumb4fun (Feb 18, 2009)

I use 3/8 wirsbo pex when repairing and rebuilding the schools drinking fountains. Works well. One thing to remember when ordering 3/8" copper tube size pex you must call out 1/4" tubing because Wirsbo goes by the inside diameter even on smaller tubing sizes. Learned this the hard way and had to send a bunch back to Ferguson's.


----------



## user823 (Feb 3, 2009)

smellslike$tome said:


> I routinely come across older houses here with 1/2" copper or galvanized water services and in houses that are all copper I often find 3/8" branches going to everything.


Alabama right?:thumbup:
Sorry, couldn't help myself.:laughing:


----------



## user823 (Feb 3, 2009)

plumb4fun said:


> I use 3/8 wirsbo pex when repairing and rebuilding the schools drinking fountains. Works well. One thing to remember when ordering 3/8" copper tube size pex you must call out 1/4" tubing because Wirsbo goes by the inside diameter even on smaller tubing sizes. Learned this the hard way and had to send a bunch back to Ferguson's.


I routinely use 3/8" pex water supplies for sinks and toilets. Still, 3/8" size of any pipe is not allowed inside walls as per the latest code.


----------



## Herk (Jun 12, 2008)

I always use 1/2" on toilets. Some of them require a fast enough supply to help flush and fill at the same time, though that's becoming a thing of the past.

Otherwise, I have no problem with 3/8" for most fixtures, unless you've got a huge whirlpool tub to fill - I've run 3/4" on those.


----------



## Indweller (Mar 12, 2009)

nhmaster3015, you are right. this is homerun pex design. 3/8" lines would run directly from manabloc manifold ports to fixtures requiring < 2GPM. 1/2" lines would run from manabloc manifold ports to fixtures requiring more GPM such as tubs, washing machines, etc. viega makes a manabloc manifold with both 3/8" and 1/2" ports.

this project is a 5-plex. lot's of older galvanized. owner pays utilities and has "green" mindset, so motivated to reduce gas and water consumption. been thinking about pex for a while now. the bottom two apartments on the first floor would lend themselves to a "homerun" pex design from manifold in basement that could feed fixtures from below. so, thinking this might be a nice project to try pex.

manifold manufacturers seem to promote using 3/8" lines where appropriate, but many people simply recommend 1/2". not sure if they have pex homerun experience or if they are applying t&b copper rules to homerun pex design which has drastically fewer fittings, 90 degree angles, etc. don't want to do something stupid that will regret later, but open to innovation. just want to get it right. has anyone installed 3/8" "homerun" from manifold to fixtures? work ok?


----------



## Redwood (Sep 8, 2008)

How about an Intro?
http://www.plumbingzone.com/newthread.php?do=newthread&f=3


----------



## Nevada Plumber (Jan 3, 2009)

There seems to be some confusion in the different types of 3/8" PEX.

There is a 3/8" CTS (1/2" OD) PEX piping that is routinely used on the Manabloc systems for running lines for lav faucets, toilets, etc. I know Viega makes a 3/8" CTS (1/2" OD) PEX x polybute coupling for repair work. Running this size from the Manabloc to the fixture will get hot water faster then if you had run 1/2" CTS (5/8" OD) PEX. Just don't try to run it for a high flow fixture.

There is also 1/4" CTS (3/8" OD) PEX pipe. This is the stuff that is used on reverse osmosys systems and as risers for the toilets and lav faucets. You have to use a compression coupling or John Guest style quick connect fitting to work with this type of pipe.

The icemaker tubing is actually called 1/8" CTS (1/4" OD) pipe.

I only post this because I have had this conversation with supply houses more then once after they have screwed up an order. If this information helps someone else not have a wrong order delivered to them, then we all win.


----------



## nhmaster3015 (Aug 5, 2008)

Most codes consider home run systems to be engineered so the 3/8 in the wall does not apply. However pressure and length of run still figure into the equation.


----------



## smellslike$tome (Jun 16, 2008)

Indweller said:


> nhmaster3015, you are right. this is homerun pex design. 3/8" lines would run directly from manabloc manifold ports to fixtures requiring < 2GPM. 1/2" lines would run from manabloc manifold ports to fixtures requiring more GPM such as tubs, washing machines, etc. viega makes a manabloc manifold with both 3/8" and 1/2" ports.
> 
> this project is a 5-plex. lot's of older galvanized. owner pays utilities and has "green" mindset, so motivated to reduce gas and water consumption. been thinking about pex for a while now. the bottom two apartments on the first floor would lend themselves to a "homerun" pex design from manifold in basement that could feed fixtures from below. so, thinking this might be a nice project to try pex.
> 
> manifold manufacturers seem to promote using 3/8" lines where appropriate, but many people simply recommend 1/2". not sure if they have pex homerun experience or if they are applying t&b copper rules to homerun pex design which has drastically fewer fittings, 90 degree angles, etc. don't want to do something stupid that will regret later, but open to innovation. just want to get it right. has anyone installed 3/8" "homerun" from manifold to fixtures? work ok?


In my opinion, a manabloc system will do just the opposite of what he says he wants.


----------



## user823 (Feb 3, 2009)

nhmaster3015 said:


> Most codes consider home run systems to be engineered so the 3/8 in the wall does not apply. However pressure and length of run still figure into the equation.


Speaking of the Minnesota Plumbing Code only, nothing is said about home run systems anywhere in the book. If someone here tried running 3/8 piping in a wall the inspector would make him rip it out. Code is very strict here, minimum 1/2" in walls period.


----------



## M5Plumb (Oct 2, 2008)

I believe you are talking about the questpex repair couplings, I sue that with the RTI crimps, mostly try to run a whole new line as long as the customer is amenable to it.





Nevada Plumber said:


> There seems to be some confusion in the different types of 3/8" PEX.
> 
> There is a 3/8" CTS (1/2" OD) PEX piping that is routinely used on the Manabloc systems for running lines for lav faucets, toilets, etc. I know Viega makes a 3/8" CTS (1/2" OD) PEX x polybute coupling for repair work. Running this size from the Manabloc to the fixture will get hot water faster then if you had run 1/2" CTS (5/8" OD) PEX. Just don't try to run it for a high flow fixture.
> 
> ...


----------



## Airgap (Dec 18, 2008)

In my opinion, manifold systems take away the craftsmanship of being a professional plumber.


----------



## plumb4fun (Feb 18, 2009)

ironranger said:


> I routinely use 3/8" pex water supplies for sinks and toilets. Still, 3/8" size of any pipe is not allowed inside walls as per the latest code.


I agree, I don't use it inside the walls unless its in a chase where the shut off valve is located.


----------



## nhmaster3015 (Aug 5, 2008)

They might very well make you tear it out here as well. You would have to prove that the length of the run and the supply pressure would deliver the minimum flow rate for the fixture served. The IPC only addresses it pretty much that way.


----------



## Protech (Sep 22, 2008)

they make 3/8"id 1/2" od sharke bites.........

You can also use plain brass compression couplings with plastic ferruls and brass stiffeners.



Ron The Plumber said:


> Stay away from te 3/8 pex off a manifold, for one thing, yes I have encountered the 3/8 as the main lines out to the fixtures, it was quest pipe, if you know what it's like to fix a leak on 3/8 in the wall and almost no way to make the transition from it to pex, almost impossible, supply house will have no way to help you in the case, I did not warranty my repair on it, I had to use a 3/8 comp x 1/2 comp quest coupling.
> 
> Just don't use this crap. I have only found it twice here and once in the walls, no way to replace a run unless you take it all the way back to the block, this was not an option.
> 
> It was not an older house.


----------



## Protech (Sep 22, 2008)

Florida code has a provision for manifold water distribution systems. You can run 3/8"ID pipe in walls and under slabs as long as it is a manifold system and the line is sized so that it supplies the flow pressure set forth in the code. It's kind of irrelevant though because if you were to run a loop long enough to actually end up under code spec'd flow pressure you would have defeated the purpose of installing a manabloc system. The idea is that you locate your heater(s) central to your fixtures and run properly sized distribution lines to each fixture. If you don't design a mana bloc system properly, then it just won't perform as advertised. I've discussed this topic before on contractortalk.com .

See here: http://www.contractortalk.com/f28/aquapex-8569/#post511627



ironranger said:


> I routinely use 3/8" pex water supplies for sinks and toilets. Still, 3/8" size of any pipe is not allowed inside walls as per the latest code.


----------



## plumberguy (Mar 7, 2009)

There is a lot of PEX used in this area due to PH problems that will eat copper for lunch. It is a rare occurance when 3/8" is used at all. 1/2" to the fxture and then 3/8" to the faucet from the stop. We sell all of the sizes at my store but do not move much 3/8" at all. This is good pipe when needed or used and there are banded couplings now to connect from PB to PEX. The good thing is that the OD is a match for copper, CPVC, PB and PEX so possibilities do exist.


----------



## kellybhutchings (Jul 29, 2008)

3/8 pex is 1/2 inch o.d. not the same as the 3/8 o.d. copper used for supply lines. I think the 3/8 inch pex would be big enough for most fixtures if manifolded, but our inspector does not allow it.


----------

