Advice on water pipe sizing.


Old 08-16-16, 09:51 PM
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Advice on water pipe sizing.

i'm gonna replace the pipes from my water meter on. i have a 1 1/4" main that then goes into a 2" that everything in the house branches off of. i have 2 flushometers in the house and 4 sinks. the lines going to the flushometers are 1 1/4". everything is galv pipe which i'm gonna replace with copper. is there a reason they used 2" pipe or can i replace everything with 1 1/4. i know flushometers use a large volume quickly and was wondering if thats the reason for the 2" run.
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Old 08-19-16, 10:23 AM
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Sorry, that's a bit out of my residential piping experience.

Typically, increasing the size of the pipe larger than the main is useless unless you have exceptionally long runs.
Old 08-19-16, 11:27 AM
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Are you SURE you have only a 1-1/4 inch main supply? It is common to use a water meter somewhat smaller than the pipe size on ether side of the meter so if you are basing the supply main at the same size as the meter without visually inspecting the incoming (to the meter) piping you might be in error. I have one inch piping on both sides of the meter but only a 3/4 inch meter.

It could also be that when the galvanized piping was installed it was upsized to allow for accumulation of rust and corrosion over its life. Copper, since it won't corrode internally, is often sized one size smaller than would be galvanized steel for the same flow rate.

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