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 pex vs copper flow rate
Author: Anonymous User

I am considering replacement of my copper water supply lines (circa 1960's) with a PEX system before I close in my basement ceilings. My question has to do with flow rate and volume of pex vs copper. I note that the ID of the 3/4" copper fittings for connecting pex is not much greater than the ID of 1/2" copper tubing and significantly less than 3/4" copper. I am not a hydraulic engineer, but wouldn't this restrict the maximum flow rate and capacity of my water supply?

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 Re: pex vs copper flow rate
Author: Dunbar (KY)

Sure would.

You need to upsize the piping to match the id of copper to be code acceptable for your plumbing system.

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 Re: pex vs copper flow rate
Author: Scott D. Plumber (VA)

If your plumbing fixtures are the good old high flow type typical of the '60s, you will notice the flow differance!

Like Dunbar said, you will need to upsize your piping for PEX to avoid flow issues.

Also, limit your joints with the PEX. That is one of it's advantages. You can get it installed with very few joints, eliminating many leak opportunities and keeping your flow to a maximum.

You should have joints at the tees and at the wall penatrations, but other than that try to make your runs in one piece.

Also use good components that secure your stub outs and keep them straight. one of the things that gives PEX a bad name is shoddy instaltion that does not make the piping secure and attractive where visible. (It should not flop all around like a garden hose!)

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 Re: pex vs copper flow rate
Author: hj (AZ)

Yes, except at low flow rates.

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 Re: pex vs copper flow rate
Author: Uni R

The fittings are restrictive but not as much as you might be thinking. You have to remember that a 3/4" ID pipe with fittings that are only 1/4" ID will have significantly more flow than a straight 1/4" ID pipe. The fittings do restrict the flow but only while the water is having to go through the fitting. The key with PEX is to minimize the fittings. To properly calculate the flow restrictions you have to measure the flow restrictions per foot of the pipe by its length and add the flow restrictions for each fitting. Different layouts will give different results so it is tough to compare PEX to Cu that way.

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