water service sizing

[bptp32]

Residential Code of NYS 2010 version (based on 2006 IRC)

I have a new SFD being constructed. the water authority speced 3/4" COPPER water service pipe from the curb box to the interior shutoff/meter assembly. The contractor switched to 3/4" Pex. Should the substitution of the pex for the copper required the pex to be increased one pipe size due to ID and resistance to flow? Our water purveyor authority stops at the curb box but has always recommended an increase in pipe size if Pex is installed as the service piping. Thanks for the help.

 

[cda]

May need to fact check;;,

Having recentely spent several weeks researching PEX for an upcoming article in FHB, I can answer a couple of your questions. First, PEX, like CPVC, comes in the same ODs as copper pipe. So, your intuition about the ID is correct. Except....PEX is smoother and has fewer fittings, so the codes accept PEX on a size for size basis with copper. If you can use 1/2 in. copper, you can use 1/2 in. PEX and expect the same or a better flow. In fact, you can often drop a size with PEX, although the savings are minimal and I wouldn't bother. Except.... You'd have to flush far less cooled water out of a 3/8 in. PEX line than any 1/2 in. line if you want hot water in your upstairs bathroom faster.

Hope that helps.

Andy

Senior Editor, Fine Homebuilding

 

[bptp32]

Thanks Andy for the quick response. I was under the assumption that since copper pipe fittings were on the exterior of the piping to be connected and on pex the fittings are on the inside of the piping, this would have an impact on flow through the fittings. The actual location of the fittings was the reason that the piping was increased one size. if the pex system was a manifold type of system with no fittings then I would agree, but I usually see the pex run the same way as copper piping with fittings at every change in direction and a main line feeding a few other branch lines. Thanks again