I’m getting ready to plumb my next house, and I am using a manifold and pex tubing in a home run layout. The brochure brags 3/8″ pipe is enough for showers, sinks etc, and even lets hot water get their quicker. It makes sense to me, since there are no “branch” circuits and most things are reduced to 3/8 after the shutoff valve anyway, but does anyone have experience w/ this setup?
Is 3/8 standard in pex homeruns? (star topology for the techies)
I despise low water flow and/or pressure.
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Mike
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Hey thanks any way - I found a chart that states for 2.5 gph applications (basically everything except tubs and outdoor spigots) 3/8 is preferable - less water wasted waiting for hot etc. So I'll be ordering the 3/8...
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We use 1/2 even on the cheapest houses. What my plumber says about is pex is since the fittings have to slip inside the tubing, they further restrict the water flow, beyond what the diameter of the tubing does. In other words, if you were to use 3/8 pex, the inside diameter of the fittings might be 1/4"!
I understand what you are saying about the advantage of a manifold, but that only comes into play when multiple fixtures are being used simultaniously.
I'd recommend that you at least get some more opinions and/or do some more research.
Thanks Matt - I hadn't thought of that issue - the mere thought of an underpowered shower, and I'm back to using 1/2"Treat every person you meet like you will know them the rest of your life - you just might!
Like I said, do some more checking around.
Don't confuse volume with pressure - a drop of water falling over Niagara Falls has the same pressure at the bottom as the Falls themselves...it's the volume that's different. Do you want drops or a shower in the bathtub? Bear in mind that, yes, maybe there's 3/8" at pex fittings and various faucets etc, but the bathtub faucets are 1/2" for a reason...to provide volume of water. I know, as a customer wished for a kitchen faucet (ie 3/8") installed in her bathtub - and it took twice as long to fill.
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To those who know - this may be obvious. To those who don't - I hope I've helped.
No!
Our plumber always uses 1/2inch Minimum
When in doubt, get a bigger hammer!
What I like is, when in doubt read the directions.
Thanks for your clear, direct answer.
Last place, I ran 3/4 direct to my tub (71 gallons) w/ a high flow faucet it filled REALLY fast - very nice.
1/2" it is (except the tub - going bigger again). I knew I'd get a straight answer from BTers
Treat every person you meet like you will know them the rest of your life - you just might!
I suppose that in a mobile hime with only a 25' run, you might get by...but we use 1/2"
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I'm not a pro, but I just built my own home.
I used 3/8" pex on my sinks and toilets from a central manifold, no problems, no regrets. I ran 1/2" to my tub, showers, bibs and kitchen, but the 2.5 gpm flow limits on my interior faucets make the output differences indistinguishable. What is noticable is how much faster you can get hot water from the 3/8" tubing vs 1/2." No question there is less wasted energy.
One of the factors in my decision to go 3/8" was the on-demand water-heater next to my manifold which has a peak output of 3 gpm. The 3/8" tubing will handle all the hot water it can get...
There are some issues r/t pressure drop from expansion tank to manifold to single use outlet when distances are greater than 50', but I haven't experience any problems in my modest three bedroom home.
Highly recommend reading about tubing and installation on the Zurn and Wirsbo web sites. Zurn in particular advocates of 3/8" for interior plumbing.
- Brian
That is very interesting...
I went to the Zurn web site and after some looking around I found what you were talking about:
http://www.zurn.com/operations/pexrh/pdfs/installation/PEXDesApplGuide.pdf looking at the page numbers at the bottom of the document (not of the PDF viewer tool) it is on page 13.
What I gather from the chart is that the velocity through the 3/8 is roughly double as compared to what it is through the 1/2". On the other hand the pressure drop is maybe 4 times greater through the 3/8 vs the 1/2". These stats are done for 100 foot runs, and I don't know if the number's change in direct proportion to the length of the run - in other words, can I assume that the pressure drop would be exactly 1/2 with a 50 foot run?
To me, tests done of 50' runs would be more meaningful for residential construction. Also, I'd like to see the numbers expressed as flow rates at, say 55 PSI at the manifold, which might be typical for a residential water supply system.
Further, I notice that the chart does not rate the 3/8" tubing at 4, 5 or 6 GPM, only at 1, 2 & 3 GPM; which would insinuate to me that the 3/8 is not suitable for higher flow rate applications.
Also, I'm guessing that this chart is only rating the tubing - not the fittings, which as I stated before, further restrict the flow.
My house is plumbed with 1/2" pex - manifold in the crawl space. The house is about 75' long, 1 story, so I'm assuming that no run is longer than 50' and probably closer to 35'. Since I don't have a life, ;-) I did a little testing. kitchen sink: 1.5 GPM, bath sink: 2 GPM, bath shower: 1.5 GPM, and master shower (water saving device removed from shower head): 2 GPM. I also know, from previous testing that the hose bibs produce 5 GPM and that is all 1/2" tubing/pipe - no "choke downs" except a the valve itself. I've always felt our water flow was fine but not great. It is a municipal water system with 14 GPM available at the meter - I tested that too when building the house.
I'd like to add though that the plumber I use now won't install pex in the mid priced houses I build - only the low priced ones - again - he cites flow issues as the reason for the difference - as stated in my first posting. I gotta think though that since he has exhibited a knack for saving a dime, he would use 3/8" pex if he thought he could get away with it...
I got his guys coming to rough in a house on Monday - if they show up... :-( and I'm gonna ask them or him about 3/8 pex. I'm sure he knows - not sure what his guys will know, especially since his well seasoned guys do the trim outs only... They will be roughing in that house with CPVC though.
We use 1/2 on any work we do. Why risk a slow fill or low volume for such a minimal upcharge? DanT
The only reason I would use 3/8 would be faster HW/ Water Heating $ savings, not materials cost. The difference in cost is negligibile (although I'd need to buy a 3/8" crimper too)
I have always use copper or cpvc, and have never plumbed an entire huse in pex, I was planning on 1/2" when I read 3/8" might have advantages.
So it look like there might be a tradeoff:
3/8" = fast HW, lower flow (is this acceptable)
1/2" = more flow, slower HW, more HW wasted
Since the runs will be <~25' everywhere, I guess 1/2" is OK for my application, not too much wait for HW. It just seems silly to plumb 1/2" then reduce it to 3/8 under the sink or at the shower head.
Treat every person you meet like you will know them the rest of your life - you just might!
My two cents...
I would look into 1/2 plus a return line for the hot water to circulate with a small pump. This provides instant hot water, great volume and water savings as you don't have to run all the water waiting for the hot water to come. When I first heard of the system I thought it would be a energy waster but consider every time you run a sink tap just to get warm water on a washcloth or quickly clean a cup. Each time you lose the entire volume of water in the pipes.
Byron
Unless you have super-insulated supply lines, a small (2-4 gal) under-sink storage heater is less expensive to operate than a recirculation system. Recirculation offers convenience and saves some water, but it almost never saves money.
1/2" works so well that this sounds somewhat like tinkering with something new for the sake of tinkering. Long waits for hot water are mostly poor hot water tank location.
It's not just diameter, length matters a lot. That's why the codes have tables for how far you can go with a particular diameter for a given fixture load.
To get a feel for this, try blowing through a long garden hose, then through a short piece of the same hose. The longer the run, the more pressure and flow rate go down.
-- J.S.
Well it's one thing to ask the salesman but your local codes over ride them I was going to attach a water sizing chart out of my code book but it's 2000 & not 2003 so if you want the deadlock no ands ifs or butts ask IAPMO international association of plumbing & mechanical officials & besides they like the attention. http://www.iapmo.org/iapmo/code_ask.html
3/8 allows for pretty good flow to a single outlet.