I’m installing PEX pipe and notice the fitting ID’s are much smaller than copper fitting ID’s (3/4″ PEX fitting ID seems very close to 1/2″ copper fitting ID, 1/2″ pex looks similar to 3/8″ copper). Is it necessary to “size up” with pex to get the same pressure and volume as copper? Intuition says yes supply house says no because of flow restrictors on most new fixtures. Any thougts? I’ve used 3/4″ pex for main lines and T off to 1/2″ for for dleivery to fixtures.
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Fine Homebuilding's editorial director has some fun news to share.
Featured Video
Highlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
I believe PEX is sized by ID. the OD is larger than ID. 1/2" PEX typically is about 5/8" OD and 1/2" ID.
I can't compare that to copper myself, but I have never been aware of any need to upsize. If in doubt, get a hold of the flow rate charts for the PEX you are using, the MFG should have that data available for you.
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
When talking about 1/2” PEX and Copper tubing, PEX OD is the same as Copper OD, and PEX ID is smaller than Copper ID.
we now have to run everything in 3/4" to within 24" of the fixture cutoff... but then in most cases you are dropping it to 3/8" anyway... which makes about zero sense with low flow faucets and toilets...
p
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
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom
Andy, did you run across this in your research?
View Image
http://cgi.ebay.com/5th-Edition-WIRSBO-COMPLETE-DESIGN-ASSISTANCE-MANUAL_W0QQitemZ6038099391QQcategoryZ42133QQrdZ1QQcmdZViewItem
It's not available locally, is it worth the price? My next project is going to be PEX so do a good job on your article.
Joe H
Joe. That book is not only worth the price, it's priceless! That's the 5th addition. The ones before it are good too. This is strictly a radiant heating manual tho.
If you buy enough Wirsbo stuff, you get it for free!!
Wirsbo's other smaller components and tools manuals for heating and plumbing are good companions to the above manual.
It is true in most cases you will have less fittings.
But a bend is a bend per-say
bends cause friction & restrict flow,
Like an electrician pullin wire through a conduit once they hit that 360 degree mark it makes it alot tougher to pull the wire.
True, but with PEX a bend might have a 6 in. radius, unlike a copper L's 1/2 in. radius. PEX isn't perfect, but I doubt I'll ever do another house in copper.Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom
An in general much fewer of those bends.Being a hack I often end up in some odd place or restriction and need a handfull of fittings to get around that would not be need with pex.
I will also add to Andy's comments that PEX is plumbed as home runs, so if more than one fixture is calling for water each is likely to have its own feed directly from the distribution manifold.
Conventionally laid-out copper piping would be drawing from one main feed line for most of its length instead- with the resulting pressure and volume drop. Of course, the larger the house and the longer the runs the more this becomes an important difference.
- Brian.
Personaly I oversize everything copper & pex.
Here is an interesting article by a plumbing contractor.
http://www.contractormag.com/articles/column.cfm?columnid=22
I'll tell you what I know, which ain't much. In the fire department we use a lot of 4" hose for supply lines. The typical setup is 5" at the hydrant with a reducer to 4" and then to the pumper.
In some scenarios we feed one pumper from another. For that we use a 2-1/2" discharge from the supplying engine, and adapt it immediately to the 4". In other words, there's a short section (less than 12") of 2-1/2" in an otherwise 4" line.
This little section of 2-1/2" does NOT effectively reduce the entire line to the flow capacity of a 2-1/2" line, it's much closer to 4". I could get some scientific facts and figures from the chief engineer but I know it's standard practice.
I was plumbing some 3/4" PEX yesterday and noticed that the fitting is fairly small ID. After setting up the branch I was working on, I opened the temp valve at the end of the PEX and got a huge amount of water out of it, at 40 PSI.
That instance is a bit different than house plumbing in that the narrower section of line (if I read your post correctly) is from one pumper to another. In this case you have an additional pump to increase pressure which would bring the water volume back up.
In the situation described in the original post, the pressure is a constant (whatever the city or well pump supplies). This means that if you decrease the pipe diameter, there will be a corresponding drop in water volume. In order to decrease pipe diameter & maintain the same volume additional pressure would be needed.
However, as other have explained, PEX is smother on the inside than copper & there are far less fittings required. This would result in less of a pressure drop in PEX than in copper which would in turn make up for the loss in volume.
I guess my point is that the short section of smaller ID has little effect. The amount of water coming from 3/4" PEX is amazing, probably more than 10 GPM. I'll get a bucket later and do a little test.
True enough that we are running 200 PSI from one pumper to another, that makes up for a lot problems with pesky little reducers.
Just use the same size you would for copper. PEX actually has a flow advantage overall with fewer sharp turns, and smooth walls.
The short answer according to this research lab’s article is that PEX and copper are so similar that you will hardly notice a difference. I feel better now about switching to PEX for my plumbing. If you’d like to read the tests and results I’ll attach the link as follows: https://www.homeinnovation.com/~/media/Files/Reports/pex_copper_pressure.pdf
Try this link for PEX manuals.
Uponor is the best! (for reference materials)
https://www.uponorpro.com/technical-support/manuals.aspx
When I finally switched to pex for domestic water piping, I chose Uponor; their fittings have a larger id. I also prefer their expansion ring connections vs crimp rings.
I've used Uponor pex for typical main & branch piping, and have also used their manifold system; both work well.
The only concern I have is rodent knawing......