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Old 11-26-2012, 07:40 PM   #1
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Water pipe sizing


I have a 1 inch water meter,which supplies a 3/4 inch cold and a 1/2 inch hot water lines.
House currently has 2 full baths,1 Lavette,Kitchen sink with Dishwasher,Washing Machine,2 hose bibs and inground sprinklers.
Looking to add a 3/4 bathroom in my basement.
Have 50 psi pressure at the meter.
House is two stories with a basement.
House was built in 2000.
Will I have enough pressure and flow for the new bathroom,or will I need a piping upgrade.

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Old 11-26-2012, 08:10 PM   #2
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Water pipe sizing


All the main runs needed to be at least 3/4" both hot and cold not just the cold line.
It's not pressure that's going to be the issue it's flow.

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Old 11-26-2012, 08:19 PM   #3
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Water pipe sizing


It all depends on the plumbing code in your state. Here in MA, you should already have 3/4" cold and hot water mains, and a 1" water service. With the addition of the new 3/4 bath, the cold water main would have to be bumped-up to 1", and the water service would have to be 1 1/4".
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Old 11-26-2012, 08:27 PM   #4
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Water pipe sizing


I'm too lazy to dig out my code book for sizing charts but you will be undersized on both hot and cold. You might squeak by with the service though
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Old 11-26-2012, 08:31 PM   #5
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Water pipe sizing


One of the cases where bigger is really better.
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Old 11-28-2012, 09:10 AM   #6
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Water pipe sizing


Need to do a new HW Heater anyway,if I repipe and make the HW line 3/4 from the cold water supply thru heater to the new basement HW takeoff and leave everything else 1/2 inch do you think it will pass muster?
Have not had any problems to date with volume or pressure throughout the house in the 12 years I've been there.
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Old 11-28-2012, 09:36 AM   #7
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Water pipe sizing


I'm not the expert here....but I have made some of those mistakes....the 1/2" is too small for you hot water...

You basically want the 3/4" to act as a main supply to each area....once you get to a bathroom tee off with a 1/2" line.

You might be ok now...but wait until you get the other bathroom going and someone flushes a tolet....

As I have mine now...you can be in the shower and flush the tolet next to it and not even know except for the sound.

One last thing.....make sure you debur the inside of those copper pipes as you run the lines. It does wonders for cutting down the noise.
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Old 11-28-2012, 11:28 AM   #8
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The answer can be found in calculating the Water Supply Fixture Units or WSFU for your house. There are code tables to show you what size of pipe is required to supply the fixtures installed in your house. As I recall, the length of the pipe runs come into the calculation too.

For example, in my case (2 bath, 1 kitchen, 1 laundry, 2 hosebibs, 75' pipe run), the tables required 1" cold and 3/4" hot mainlines.
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Old 11-28-2012, 11:34 AM   #9
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Boy....looks like I'll be in trouble......

I have a 3/4" line coming in ......3 full baths....laundry.....kitchen....
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Old 11-28-2012, 11:37 AM   #10
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Quote:
Originally Posted by ddawg16 View Post
Boy....looks like I'll be in trouble......

I have a 3/4" line coming in ......3 full baths....laundry.....kitchen....
No doubt installed to code at the time the house was built, so you're good. On the other hand, I gutted and replumbed 99% of the pipes, so I wasn't grandfathered in.

I'm not sure how grandfathering applies when only upgrading part of a plumbing system though.
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Old 11-28-2012, 11:39 AM   #11
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Quote:
Originally Posted by tylernt View Post
No doubt installed to code at the time the house was built, so you're good. On the other hand, I gutted and replumbed 99% of the pipes, so I wasn't grandfathered in.

I'm not sure how grandfathering applies when only upgrading part of a plumbing system though.
Not exactly....I'm in the middle of a 2-story addition right now...I added 2 bathrooms.....laundry got moved from the kitchen to the addition....
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Old 11-28-2012, 11:41 AM   #12
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Not exactly....I'm in the middle of a 2-story addition right now...I added 2 bathrooms.....laundry got moved from the kitchen to the addition....
Well... hopefully the inspector passes it then. Maybe offer a 12-pack to take home with him?
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Old 11-28-2012, 11:45 AM   #13
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I bribe him with a Pepsi every time he shows up...we actually joke about it......

There is nothing on my prints regarding it....so the chances are they won't make an issue of it....
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Old 11-28-2012, 11:53 AM   #14
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Water pipe sizing


There's actually 2 major steps to sizing water. First is the service- you need to know the lowest minimum pressure supplied(it does vary). Elevation from the source to the highest outlet. Length of service line and the water fixture units calcs. for the house. Once you have this info you can refer to the sizing charts in your local code book.
Now you know the service size, then you need to calc the CW and HW lines seperatly inside the home based on each fixtures water fixture units. There are some general rule of thumbs that plumbers follow such as 2 fixtures on a 1/2" line. But I've been bit by that rule also- such as soaker tubs and elaborate showers
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Old 11-28-2012, 02:41 PM   #15
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Water pipe sizing


I'm looking at the residential code trying to figure out my WSFU's for a 1 inch meter with a 3/4 inch distribution pipe and alas,that combination doesn't exist in the code.
Are I an idiot (a distinct possibility),or did a druken plumber build my house?
Either way,since my Hot Water branch circuits are 1) 1/2 to the kitchen 2) 1/2 to the two upstairs bathrooms 3) 1/2 to first floor lavette and 4) 1/2 to washing machine,that if I upgrade my distibution pipe from 1/2 to 3/4 I should be OK both pressure and flowwise,and in the eyes of the plumbing law,are I coorect in this assumption?

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