Is 3/4" Pex Necessary? - Plumbing - Contractor Talk

Is 3/4" Pex Necessary?

 
Thread Tools Search this Thread Display Modes
Old 11-08-2019, 10:24 AM   #1
Pro
 
BlueRidgeGreen's Avatar
 
Trade: Craftsman
Join Date: Apr 2012
Location: Middlebrook, Va
Posts: 2,926
Rewards Points: 10

Is 3/4" Pex Necessary?


I'm building this house that has very long runs.

125' from end to end.

My water supply will be roughly 50' and 75' away from the furthest fixtures...respectively.

My intention was to run a manifold system using copper manifolds with 1" inlets and soldered on 3/4" pex valve outlets.
(I found a couple made by Sioux Chief that fit the bill.)

Basically, each bathroom (two of them being the farthest points) and the kitchen (30') will have 3/4" pex supplies that branch as they arrive at the fixtures.

The Master Bath is obviously the most important, and is the 50' run.


Questions....
Am I overbuilding this thing?
Would 1/2" home runs be sufficient for speed of hot water to fixtures and pressure at fixtures?
Would the volume in 3/4" actually slow the delivery of hot water (from a Stiebel electric on demand)?

After a great thread years ago (by a plumber who is long gone) about Pex diameter, fittings, and pressure loss; I've been running 3/4" to everything with good results.

Just wondering what you experts think about this situation though.

Thanks in advance,
Jonathan
__________________
"Timid men prefer the calm of despotism to the tempestuous sea of liberty". Thomas Jefferson
BlueRidgeGreen is online now  

Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ContractorTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

   

Advertisement

 

Old 11-08-2019, 11:31 AM   #2
Pro
 
Mordekyle's Avatar
 
Join Date: May 2014
Posts: 2,454
Rewards Points: 5,156

Re: Is 3/4" Pex Necessary?


Price difference?


Sent from my iPhone using Tapatalk

Advertisement

Mordekyle is online now  
Old 11-08-2019, 11:51 AM   #3
Fire up the BBQ
 
griz's Avatar
 
Trade: GC
Join Date: Nov 2009
Location: CA
Posts: 22,345
Rewards Points: 10

Re: Is 3/4" Pex Necessary?


I always did the same, 3/4 on long runs.

Dont forget to run a circ line for the hot water.
__________________
SOME JOBS JUST AREN'T WORTH DOING:
griz is online now  
The Following User Says Thank You to griz For This Useful Post:
Seven-Delta-FortyOne (11-08-2019)
Sponsored Links
Advertisement
 
Old 11-08-2019, 11:58 AM   #4
Pro
 
BlueRidgeGreen's Avatar
 
Trade: Craftsman
Join Date: Apr 2012
Location: Middlebrook, Va
Posts: 2,926
Rewards Points: 10

Re: Is 3/4" Pex Necessary?


Quote:
Originally Posted by Mordekyle View Post
Price difference?


Sent from my iPhone using Tapatalk


Canít be that much.

Worth it if it beats those long runs.


Sent from my iPhone using Tapatalk
__________________
"Timid men prefer the calm of despotism to the tempestuous sea of liberty". Thomas Jefferson
BlueRidgeGreen is online now  
Old 11-08-2019, 12:18 PM   #5
John the Builder
 
SmallTownGuy's Avatar
 
Trade: Carpenter/Builder Professional Painter
Join Date: Sep 2012
Location: Oxford, MI
Posts: 16,973
Rewards Points: 5,378

Re: Is 3/4" Pex Necessary?


hmmm. Firstly, that you use electric.
Here, use gas almost exclusively. Two levels - one heater and furnace on each level. Shorter runs and less water cooling off in the supplies.
__________________
All my Life loving Hippie friends turned into soul-sucking Conservatives - or died. Same difference.
"Mornin' ladies, my goodness don't you look happy. Must be cuttin' somebody up pretty good." - Andy Griffiths
SmallTownGuy is online now  
Old 11-08-2019, 01:13 PM   #6
Pro
 
BlueRidgeGreen's Avatar
 
Trade: Craftsman
Join Date: Apr 2012
Location: Middlebrook, Va
Posts: 2,926
Rewards Points: 10

Re: Is 3/4" Pex Necessary?


Quote:
Originally Posted by SmallTownGuy View Post
hmmm. Firstly, that you use electric.

Here, use gas almost exclusively. Two levels - one heater and furnace on each level. Shorter runs and less water cooling off in the supplies.


Iíve used the Stiebel electrics a bunch.
They are great.

It will be great for this build because no one seemed to consider mechanicals AT ALL during the design phase and venting would be a PITA (and likely enrage their aesthetic sensibilities).

Levels?
Furnace?
Huh?


Sent from my iPhone using Tapatalk
__________________
"Timid men prefer the calm of despotism to the tempestuous sea of liberty". Thomas Jefferson
BlueRidgeGreen is online now  
Old 11-08-2019, 01:15 PM   #7
Pro
 
BlueRidgeGreen's Avatar
 
Trade: Craftsman
Join Date: Apr 2012
Location: Middlebrook, Va
Posts: 2,926
Rewards Points: 10

Re: Is 3/4" Pex Necessary?


Quote:
Originally Posted by griz View Post
I always did the same, 3/4 on long runs.



Dont forget to run a circ line for the hot water.


The circ line is another issue.

Based on my research, it seems Iím better off just installing a small point-of-use under the Master Bath and forego trying to run a recirc with a tankless.


Sent from my iPhone using Tapatalk
__________________
"Timid men prefer the calm of despotism to the tempestuous sea of liberty". Thomas Jefferson
BlueRidgeGreen is online now  
Old 11-08-2019, 01:38 PM   #8
Pro
 
Randy Bush's Avatar
 
Trade: Exterior Remodeling
Join Date: Mar 2011
Location: Great Falls, MT
Posts: 5,615
Rewards Points: 1,690

Re: Is 3/4" Pex Necessary?


One plumber I know use to run only 1/2 for the hot on long runs, not so much water to run before it got hot.
Randy Bush is online now  
The Following 3 Users Say Thank You to Randy Bush For This Useful Post:
BlueRidgeGreen (11-08-2019), Mordekyle (11-08-2019), SmallTownGuy (11-08-2019)
Old 11-08-2019, 01:53 PM   #9
Goin' Down in Flames....
 
Seven-Delta-FortyOne's Avatar
 
Trade: Highwayman
Join Date: Mar 2011
Location: Somewhere Between Heaven And Hell
Posts: 4,205
Rewards Points: 540

Re: Is 3/4" Pex Necessary?


It's an electric tankless?

You (they) are going to be waiting a loooong time for hot water. With no re-circ, 75' runs, and an electric, or any tankless, and, yea, it'll be a wait.

I'd go with the 3/4 if you're doing a bathroom group on one home run. It would more than likely be required where I am anyway.
Seven-Delta-FortyOne is offline  
Old 11-08-2019, 02:01 PM   #10
Pro
 
BlueRidgeGreen's Avatar
 
Trade: Craftsman
Join Date: Apr 2012
Location: Middlebrook, Va
Posts: 2,926
Rewards Points: 10

Re: Is 3/4" Pex Necessary?


Quote:
Originally Posted by Randy Bush View Post
One plumber I know use to run only 1/2 for the hot on long runs, not so much water to run before it got hot.


Thatís exactly what Iím thinking.

But what do I lose in pressure?

Thatís why Iím thinking point of use for the Master using 3/4.....no worries at all.



Sent from my iPhone using Tapatalk
__________________
"Timid men prefer the calm of despotism to the tempestuous sea of liberty". Thomas Jefferson
BlueRidgeGreen is online now  
Old 11-08-2019, 02:02 PM   #11
Pro
 
BlueRidgeGreen's Avatar
 
Trade: Craftsman
Join Date: Apr 2012
Location: Middlebrook, Va
Posts: 2,926
Rewards Points: 10

Re: Is 3/4" Pex Necessary?


Quote:
Originally Posted by Seven-Delta-FortyOne View Post
It's an electric tankless?



You (they) are going to be waiting a loooong time for hot water. With no re-circ, 75' runs, and an electric, or any tankless, and, yea, it'll be a wait.



I'd go with the 3/4 if you're doing a bathroom group on one home run. It would more than likely be required where I am anyway.


The Stiebel electrics are fantastic.

Iíve got a few operating on 40í + runs right now with zero issues.

I used to think the same thing.


Sent from my iPhone using Tapatalk
__________________
"Timid men prefer the calm of despotism to the tempestuous sea of liberty". Thomas Jefferson
BlueRidgeGreen is online now  
The Following User Says Thank You to BlueRidgeGreen For This Useful Post:
Seven-Delta-FortyOne (11-08-2019)
Old 11-08-2019, 02:07 PM   #12
Goin' Down in Flames....
 
Seven-Delta-FortyOne's Avatar
 
Trade: Highwayman
Join Date: Mar 2011
Location: Somewhere Between Heaven And Hell
Posts: 4,205
Rewards Points: 540

Re: Is 3/4" Pex Necessary?


Quote:
Originally Posted by BlueRidgeGreen View Post
Thatís exactly what Iím thinking.

But what do I lose in pressure?

Thatís why Iím thinking point of use for the Master using 3/4.....no worries at all.



Sent from my iPhone using Tapatalk
It's more a volume thing.

Pressure will be fine with one lav faucet running, it's when you get all 3 heads in the shower going and then someone flushes the WC.
Seven-Delta-FortyOne is offline  
Old 11-08-2019, 02:08 PM   #13
John the Builder
 
SmallTownGuy's Avatar
 
Trade: Carpenter/Builder Professional Painter
Join Date: Sep 2012
Location: Oxford, MI
Posts: 16,973
Rewards Points: 5,378

Re: Is 3/4" Pex Necessary?


There'd have to be a compelling logistics issue here to spec tankless. Electricity is def not cheap in these parts.
__________________
All my Life loving Hippie friends turned into soul-sucking Conservatives - or died. Same difference.
"Mornin' ladies, my goodness don't you look happy. Must be cuttin' somebody up pretty good." - Andy Griffiths

Last edited by SmallTownGuy; 11-08-2019 at 02:35 PM.
SmallTownGuy is online now  
Old 11-08-2019, 02:56 PM   #14
Pro
 
hdavis's Avatar
 
Trade: remodeling
Join Date: Feb 2012
Location: CoastalME
Posts: 24,602
Rewards Points: 154

Re: Is 3/4" Pex Necessary?


This is one of the few cases I wouldn't consider going with the minimum demand would require.

Shower heads get changed, flow restricters/aerators get changed, and next thing you know your plumbing sux.

If anything, oversize it. It costs way too much to redo later.
hdavis is online now  
Old 11-08-2019, 05:28 PM   #15
Pro
 
tjbnwi's Avatar
 
Trade: Remodeling
Join Date: Feb 2009
Location: Cedar Tucky, Indiana
Posts: 10,270
Rewards Points: 20

Re: Is 3/4" Pex Necessary?


I’d go with a small POU water heater fed from the tankless, 3/4 to 1/2 out unless there is a tub filler, then 3/4 to the tub filler.

Tom
tjbnwi is online now  
The Following User Says Thank You to tjbnwi For This Useful Post:
BlueRidgeGreen (11-08-2019)
Old 11-08-2019, 06:00 PM   #16
Pro
 
BlueRidgeGreen's Avatar
 
Trade: Craftsman
Join Date: Apr 2012
Location: Middlebrook, Va
Posts: 2,926
Rewards Points: 10

Re: Is 3/4" Pex Necessary?


Quote:
Originally Posted by tjbnwi View Post
Iíd go with a small POU water heater fed from the tankless, 3/4 to 1/2 out unless there is a tub filler, then 3/4 to the tub filler.

Tom


Thereís a tub filler.

I think Iím going to stick with the original plan of 3/4 to everything else also.


Sent from my iPhone using Tapatalk
__________________
"Timid men prefer the calm of despotism to the tempestuous sea of liberty". Thomas Jefferson
BlueRidgeGreen is online now  
Old 11-08-2019, 06:01 PM   #17
Pro
 
BlueRidgeGreen's Avatar
 
Trade: Craftsman
Join Date: Apr 2012
Location: Middlebrook, Va
Posts: 2,926
Rewards Points: 10

Re: Is 3/4" Pex Necessary?


Quote:
Originally Posted by SmallTownGuy View Post
There'd have to be a compelling logistics issue here to spec tankless. Electricity is def not cheap in these parts.


I havenít installed a tanked WH in ...over a decade.




Sent from my iPhone using Tapatalk
__________________
"Timid men prefer the calm of despotism to the tempestuous sea of liberty". Thomas Jefferson
BlueRidgeGreen is online now  
Old 11-08-2019, 06:47 PM   #18
Pro
 
dave_dj1's Avatar
 
Trade: general contractor
Join Date: Mar 2010
Location: Upsate Ny/Vt border
Posts: 1,012
Rewards Points: 1,138

Re: Is 3/4" Pex Necessary?


3/4" PEX isn't much if any larger than 1/2" copper, I wouldn't want 75' run with 1/2" copper. Maybe run a loop of 1" and tee off it where you need it?
dave_dj1 is offline  
Old 11-08-2019, 06:53 PM   #19
Capra aegagrus

 
Tinstaafl's Avatar
 
Trade: Remodeler
Join Date: Jan 2008
Location: Central Pennsylvania
Posts: 23,394
Rewards Points: 2

Re: Is 3/4" Pex Necessary?


I'm not a fan of tankless, but hey, that's just me.

Couple years back, we built a house with some pretty long runs, and used 1/2" CPVC to get the hot water there quicker (no high-volume demand). Inspector made us use 3/4" instead, and sure enough, it took forever and a day to get hot water at the point of use.

Fortunately, we never removed the 1/2" we ran initially. Once the 3/4" we added passed inspection, just flipped a couple of valves to use the original 1/2".

One thing to keep in mind is that 3/4" pex fittings effectively reduce flow to somewhere around 1/2" pipe due to their internal diameter. For really long runs, it might be a good idea to consider a circ pump either way.
Tinstaafl is offline  
Old 11-08-2019, 06:54 PM   #20
Pro
 
Randy Bush's Avatar
 
Trade: Exterior Remodeling
Join Date: Mar 2011
Location: Great Falls, MT
Posts: 5,615
Rewards Points: 1,690

Re: Is 3/4" Pex Necessary?


Quote:
Originally Posted by BlueRidgeGreen View Post
Thatís exactly what Iím thinking.

But what do I lose in pressure?

Thatís why Iím thinking point of use for the Master using 3/4.....no worries at all.



Sent from my iPhone using Tapatalk
I don't think you lose pressure, or very little, just volume. But I could be wrong too.

Advertisement

Randy Bush is online now  


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Join Now... It's Fast and FREE!

I am a professional contractor
I am a DIY Homeowner
Drywall Talk is for
PROFESSIONAL CONTRACTORS ONLY!

At DrywallTalk.com we cater exlusivly to professional contractors who make their living as a contractor. Knowing that many homeowners and DIYers are looking for a community to call home, we've created www.DIYChatroom.com DIY Chatroom is full of helpful advices and perfect for DIY homeowners.

Redirecing in 10 seconds
No Thanks
terms of service

Already Have an Account?