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 Water supply line sizing
Author: PDX_Livin (OR)

Hi all,

I'm in the process of finishing my basement and am looking for some help with sizing my supply (PEX) lines. I'm trying to follow code and according to the "water supply fixture units" table (table 610.3) I have 31 fixture units, but am hoping to maintain capacity for up to 37 fixture units for possible additions in the future. Based off of the "fixture unit table for determining pipe size" table (table 610.4) with my 150' of developed length, pressure just under 60 psi, and 3/4" meter and street service it says that I need to have up to 1.25" lines for the main supply lines.

My issue is that 1.25" seems really large for a residential project (I know 31 or 37 fixture units is a lot, but is it that out of the norm?) and my understanding is that 3/4" or sometime 1" main supply lines tend to be standard. Also, I just had a company install a new 1" line between the meter and house and they assured me that it would be sufficient for my needs.

If anyone has feedback on this I'd love the help. Am I making a mistake in my calculations? Is over 30 fixture units for a home unusually large? Do people just not normally pay attention to this part of the code?

Thanks for the help!

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 Re: Water supply line sizing
Author: bernabeu (SC)

The code is the MINIMUM required by law for human occupation.

It is good practice to EXCEED the MINIMUM requirement.

If code states 1-1/4 I would actually use 1-1/2.

'Most' homes are originally constructed to absolute code minimum with no allowance for expansion.


"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

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 Re: Water supply line sizing
Author: packy (MA)

i would change the meter to 1 inch and run a 1 inch main.
unless you change the water heater you are only working with a 3/4 inlet/outlet at the existing heater.
chances of you turning everything on at once and flushing all the toilets are pretty remote.

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