# Water piping



## PlumbRob7 (Feb 7, 2011)

On a few commercial jobs I've been now the engineer has requested a 3/4" line (for more flow) that reduces to 1/2" before coming out of the wall for a flush tank WC with a 3/8" supply tube .... Is that good practice or overkill?


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## 504Plumber (Jan 26, 2011)

PlumbRob7 said:


> On a few commercial jobs I've been now the engineer has requested a 3/4" line (for more flow) that reduces to 1/2" before coming out of the wall for a flush tank WC with a 3/8" supply tube .... Is that good practice or overkill?


What was being done before? 3/8 galvanized????


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## PlumbRob7 (Feb 7, 2011)

Usually a 1/2" pipe for whatever you are using.. copper/pex/PVC/wirsbow
galvanized steel is not accepted anymore for new installations


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## U666A (Dec 11, 2010)

Your braided (or ridgid) supply is only 3/8 ID. 1/2 ID from the trunk to the stop should be well sufficient.

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## AKdaplumba (Jan 12, 2010)

PlumbRob7 said:


> Usually a 1/2" pipe for whatever you are using.. copper/pex/PVC/wirsbow
> galvanized steel is not accepted anymore for new installations


Here you can only use it if you're replacing existing galvanized


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## Protech (Sep 22, 2008)

Yeah but it's only for 12".

If you had 100' of 1/2" branch line vs 100' of 3/4", it would make a noticeable difference in flow.



U.A.til.I.die said:


> Your braided (or ridgid) supply is only 3/8 ID. 1/2 ID from the trunk to the stop should be well sufficient.
> 
> Sent from my iPhone using PlumbingZone


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## PlumbRob7 (Feb 7, 2011)

If you piped 100' of 3/4" and reduced to 1/2" at the end of the run would that still have a noticable difference in flow ?


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## BROOKLYN\PLUMB (May 21, 2010)

PlumbRob7 said:


> If you piped 100' of 3/4" and reduced to 1/2" at the end of the run would that still have a noticable difference in flow ?



as apposed to 1/2" all the way yes


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## U666A (Dec 11, 2010)

Protech said:


> Yeah but it's only for 12".
> 
> If you had 100' of 1/2" branch line vs 100' of 3/4", it would make a noticeable difference in flow.


Yeah, sorry. I tend to think of things in relation to my own circumstances.

From the meter, to the w/h to the toilet is only about 8' in my house. Wouldn't make much difference in flow I wouldn't think.

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## rocksteady (Oct 8, 2008)

Your toilet is 8' from your water meter? 







Paul


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## U666A (Dec 11, 2010)

rocksteady said:


> Your toilet is 8' from your water meter?
> 
> Paul


Directly above.

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## stillaround (Mar 11, 2009)

A bit much speculation...there is some REAL math to figure this. Noticeable in what sense...at a watercloset??........If the system was frought with ells then maybe 3 to 5 lbs would be noticeable assuming the overall pressure was 60 or lower.


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## Tommy plumber (Feb 19, 2010)

PlumbRob7 said:


> On a few commercial jobs I've been now the engineer has requested a 3/4" line (for more flow) that reduces to 1/2" before coming out of the wall for a flush tank WC with a 3/8" supply tube .... Is that good practice or overkill?


 



Typical engineer, they over-size things thinking more is better. In my humble opinion, that is overkill.


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## lma1 (Feb 14, 2011)

PlumbRob7 said:


> On a few commercial jobs I've been now the engineer has requested a 3/4" line (for more flow) that reduces to 1/2" before coming out of the wall for a flush tank WC with a 3/8" supply tube .... Is that good practice or overkill?


A commercial (I take it as being _public_) F-T WC has an assigned 5 WSFU ( as per 2006 BCPC). The load is equivalent to 4.5 GPM. Based on the velocity limitation of Cu pipe of ≤ 5 FPM (a Code req’t), a ¾” supply size is required. You may use any Pipe Flow Velocity tables issued by the city or municipality in question or other acceptable equivalents (E.g. ASPE Data Book) to arrive at that size. The Code further permits a ¼”ID tail piece or connector not more than 29.5” long be used to connect to that fixture (WC). Remember also our Code table states the min. water supply pipe to this WC is 3/8” NPS. 

If you use anything thing other than Cu or PVC as permitted for the type of building occupancy, you may increase the velocity limit to ≤ 8 FPM (depending on the City & AHJ) and in that case, 1/2” pipe is acceptable.

The question is not whether it’s an overkill, it’s the local Code requirement. The AHJ just upholds the law and the Engineer tries to fulfill his obligation. We’ve been doing this since the 2006 Code came into effect.


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## PlumbRob7 (Feb 7, 2011)

A 3/4" min. supply would depend on the length of the run and the pressure range... In this situation the longest run is less than 72'/24m and the pressure is 60 psi.. You would be allowed 7 Fu's on a 1/2" line ... They want 3/4" fine.. I don't understand a 3/4" line reducng to 1/2" coming out of the wall .. Why reduce to 1/2" ?... On a short distance reducing defeats the purpose of the 3/4" wouldn't it??


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## easttexasplumb (Oct 13, 2010)

Even with poor pressure and undersized pipes how long does it take to get 1.6 gallons of water.


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## lma1 (Feb 14, 2011)

PlumbRob7 said:


> A 3/4" min. supply would depend on the length of the run and the pressure range... In this situation the longest run is less than 72'/24m and the pressure is 60 psi.. You would be allowed 7 Fu's on a 1/2" line ... They want 3/4" fine.. I don't understand a 3/4" line reducng to 1/2" coming out of the wall .. Why reduce to 1/2" ?... On a short distance reducing defeats the purpose of the 3/4" wouldn't it??


After 1985, the Code added the velocity limit clauses. Since then we’ve learned to use the “velocity method” (one of the many methods cited in ASPE Data Books.) to size mostly copper-pipe based domestic water supply systems and as a last step in that method we do check the average pressure loss (PSI/ft.) in the system to ensure the loss is within the pressure available. 

You are correct in asserting that “a 3/4" min. supply would depend on the length of the run and the pressure range…” The ¾” line comes from the velocity limitation given the accepted WSFU for the WC based on its type, use & the building it’s in and its GPM (or l/s) flow equivalent. And indeed if the summer static pressure is low or inadequate, a bigger size, a larger system or a booster pump might be required. But the min. supply is still ¾” to this WC if the line is a copper or PVC. The 3/8” NPS connection size and the flow pressure (15 or 30 PSIG) for a tank type or FV WC are the min. required as prescribed by the Code. You will therefore somehow have to reduce the ¾” to this ½” connection. 

It’s not exactly correct or a bit sweeping to say “You would be allowed 7 Fu's on a 1/2" line ... They want 3/4" fine.” Even a 7.0 CWSFU non-FV fixture or a branch serves this sum of more than one non-FV fixtures has a flow equivalent of 5.7 GPM. This definitely requires a ¾” Cu or PVC line (unless it’s a pex, PE, CPVC or CI line). I suspect you might just be looking at the pressure range tables (a lot of plumbers do) and decided a ½” copper pipe is good enough for a 7.0 FU fixture or bunch of fixtures. You would be right 50% if you stop there. You *MUST* also look at the velocity limit to up-size it as necessary! 

I might agree with you in some installation this seems to be impractical & “absurd.” For example, if the supply coming out from a larger line feeding this WC that requires a ¾” line and is ≈ or not much longer than 750 mm from the WC, I would agree with you that you run it straight as a ½”.


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## plumber666 (Sep 19, 2010)

I be watching myself on our little school addition today as I start to lay out my water piping.What I do recall doing in the last few years is, always running 1" to the last two tank toilets, and using a 1"x1/2"x1/2" tee to connect them.


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## vond93 (Mar 20, 2011)

*good practice*

this is a good practice they want you to do this because of volume most likely if you ran a battery of water closets all on half inch and there was a large demand 1/2 inch couldnt provide enough volume but 3/4 ups the volume a little more in case a bunch of fixtures are in use that w/c has its demand


PlumbRob7 said:


> On a few commercial jobs I've been now the engineer has requested a 3/4" line (for more flow) that reduces to 1/2" before coming out of the wall for a flush tank WC with a 3/8" supply tube .... Is that good practice or overkill?


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## plumber666 (Sep 19, 2010)

Opened a big worm can on Friday. This 8 classroom school addition I'm on has 6 w/c's, 5 lavs, a shower, 8 sinks (with bubblers), a hose bibb and 2 flush valve urinals. Where we tie into existing, the engineer shows us bringing 1 1/4" copper into the new section. Because of the flush valves, (a local inspector helped me out, I'm no good at water pipe sizing) the feed should be 2 1/2". The hot is a 1" line and the recirc is 1/2". I haven't seen a 1/2" recirc in ages, and I'm sure the hot is too small too. 

I smell an extra..... Hope to get more info today from the engineer, sounded pi$$ed at himself Friday when I broke the news.


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## U666A (Dec 11, 2010)

vond93 said:


> ... 1/2 inch couldnt provide enough volume but 3/4 ups the volume a little more...


It actually increase the volume by a factor of 2.24 times, which is exponentially higher.

Math math math... I love math!

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## lma1 (Feb 14, 2011)

plumber666 said:


> Opened a big worm can on Friday. This 8 classroom school addition I'm on has 6 w/c's, 5 lavs, a shower, 8 sinks (with bubblers), a hose bibb and 2 flush valve urinals. Where we tie into existing, the engineer shows us bringing 1 1/4" copper into the new section. Because of the flush valves, (a local inspector helped me out, I'm no good at water pipe sizing) the feed should be 2 1/2". The hot is a 1" line and the recirc is 1/2". I haven't seen a 1/2" recirc in ages, and I'm sure the hot is too small too.
> 
> I smell an extra..... Hope to get more info today from the engineer, sounded pi$$ed at himself Friday when I broke the news.


As we don’t know the layout of your system exactly, we’ll venture to guess the feed size thus:

We’ll make the assumptions that (i) the WC’s are T-T (tank-type) which you did not say, (ii) we’ll just ignore the load contribution of the HB for this exercise as its location is not given by you in relation to the WS system (as HB is considered a “continuous flow” fixture by the Code & ASPE, you have to add the flow ‘separately’ unless if it’s the most upstream of the bunch of fixtures, you add the GPM or l/s to the total), (iii) the SK is considered “service” sinks & (iv) all fixtures are “public”.

The sum of the FU w/o the HB is = 30 (6 FU/T-T WC/each x 5) + 10 (2 FU/LAV) x 5) + 4 (4 FU/ SH x 1) + 24 (3 FU/SK ea x 8) + 10 (2 FU/F-V UR/each x 5) = 78.0.

The flow load of 78 WSFU which is 61.3 GPM (3.87 l/s). This requires a >= 2-1/2” copper. 

If we make one further assumption that the HB is located upstream of all fixtures in the feed, The flow becomes of (61.3 + 6) = 67.3 GPM (4.25 l/s). A 2-1/2” copper will also satisfy the design.


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## plumber666 (Sep 19, 2010)

Thanks Ima, for your pipe sizing. Do you have a few minutes to figure if we change the flush valves to 1/2" metering valves? I'm still sure 1 1/4" is too small, but I really need to brush up on my sizing big time.


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## plumber666 (Sep 19, 2010)

plumber666 said:


> Thanks Ima, for your pipe sizing. Do you have a few minutes to figure if we change the flush valves to 1/2" metering valves? I'm still sure 1 1/4" is too small, but I really need to brush up on my sizing big time.


 
PS, yes, the 3/4" hose bibb is at the end of the line, and the W/C's are tanks.


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## plumber666 (Sep 19, 2010)

Gave myself a refresher last night on water pipe sizing, glad I did. Was about time. On my job, subbing metering valves drops the cold main to 2". What I didn't mention was there are 5 sinks in the existing crawlspace that will be added to the line. We're ripping out 60' of existing 1" cold and supposedly upgrading to 1 1/4".
The engineer on this one has really dropped the ball. The existing hot is 1", and should be 1 1/2", and the recirc. is 1/2" which might be OK provided the flow is only 2.9 gpm.
Best solution to meet code? Run a new 2 1/2" to the water meter station. New 1 1/2" to the HW storage tanks. Dial the recirc down to SFA.
On the plus side, this engineer loves getting out of the office around 11am on Fridays so he'll be into a site visit. Then I'll show him the sizing drawings I drew up and see if he wants to get a sweet change notice rolling. Gonna suck, but I know I'll have to get the GC and architects involved.


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## lma1 (Feb 14, 2011)

plumber666 said:


> Gave myself a refresher last night on water pipe sizing, glad I did. Was about time. On my job, subbing metering valves drops the cold main to 2". What I didn't mention was there are 5 sinks in the existing crawlspace that will be added to the line. We're ripping out 60' of existing 1" cold and supposedly upgrading to 1 1/4".
> The engineer on this one has really dropped the ball. The existing hot is 1", and should be 1 1/2", and the recirc. is 1/2" which might be OK provided the flow is only 2.9 gpm.
> Best solution to meet code? Run a new 2 1/2" to the water meter station. New 1 1/2" to the HW storage tanks. Dial the recirc down to SFA.
> On the plus side, this engineer loves getting out of the office around 11am on Fridays so he'll be into a site visit. Then I'll show him the sizing drawings I drew up and see if he wants to get a sweet change notice rolling. Gonna suck, but I know I'll have to get the GC and architects involved.


The sum of the HWS FU is, if I count your fixtures correctly = 7.5 (1.5 FU/LAV x 5) + 29.25 [2.25 FU/ KS x (8 new + 5 old SK)] + 3 (3 FU/SH x 1) = 39.75 FU. This translates into 24.3 GPM. The HWS size should therefore be ≥ 2” copper based on 4FPS velocity. The 1-1/2” you mentioned might not be adequate.

2.9 GPM recirc line requires a ≥ ¾” copper line based on 3 FPS velocity and not ½” which is only good for up to 2.18 GPM (1.0 FU). 

I offer the above strictly as a guide only. I am here not to do any design. You must consult with your Engineer, GC & any AHJ to come to some kind of agreement.


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