I’m getting ready to install AquaPEX tubing in my home. I had planned to use a compression-style Manabloc with all homeruns, using 3/8″ PEX (to minimize hot water wait times and the number of connections) for everything but my bathtub and hose bibs.
I called Uponor today and spoke to one of their technicians about their expander tool and fittings. During our conversation, this Uponor tech told me that they don’t recommend homerun systems, and that, depending on the length of the run, 3/8″ PEX may well not deliver enough water for some fixtures.
In fact, he told me that according to their figures, you lose 3 psi of water pressure per foot for 3/8″ PEX. So it would seem that any runs much over 20′ would be impractical.
So this made me go back and look at what I based my 3/8″ plans on. A Breaktime member was good enough to send me a Vanguard/Manabloc design worksheet. That worksheet recommends 3/8″ PEX for everything but bathtubs and hose bibs, and doesn’t mention length of run at all.
This is a huge issue that I have to get right. Can any of you tell me from experience if my plans to use 3/8″ are flawed?
Replies
Lot of mixed up information there.
First thing - home runs are one of the great advantages and selling points behind the idea of going with pex instead of copper. Why a techie would divert you from that is confusing to me.
Next up, he is right that as a general rule, you would have reduced flow with 3/8" for over about 25 feet of run that would make it unacceptable, IMO.
same reduction with copper too. Simple fluid dynamics. That is why 1/2" copper is standard.
The advantage of the pex over copper is that 90° elbows reduce flow farther.
I think he was wrong or that you misunderstood him tho on reduced pressure. The pressure will remain the same. It is the flow that reduces. I wonder it he meant 3% rather than three pounds. At three pounds per foot reduction, you would have no pressure at all after 15 feet or so.
Personally, I would go with 1/2". Keeping all lines and fittings the same size simplifies things.
A lot!
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I told him I was having a hard time wrapping my head around the concept of his company not favoring homeruns. But that is exactly what he told me. In fact, he's going to email some design manual they have to me that shows how they'd install a PEX system.
He actually said 3 psi. When he said that, I told him that my house is regulated down to about 65 psi, so even 20' would be a huge problem for me given what he was saying. Maybe he was wrong about that. I'd sure like to know.
I do agree with you that 1/2" would make it simpler. This kind of makes me regret basing my decisions on the Manabloc worksheet. Unfortunately, I've already run 3/8" to one vanity and toilet (and closed the walls). So I'd need the 3/8" expander head and some 3/8" fittings no matter what.
3/8" is plenty for a toilet or vanity! I wouldn't want that for showers or kitchen tho.I think the guy is all wet.
Behind the ears too.
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"In fact, he told me that according to their figures, you lose 3 psi of water pressure per foot for 3/8" PEX."
That number can't be right.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Yeah, it sounded off to me, too. But that's what he insisted on. I asked him several questions revolving around how that kind of drop would affect my installation plans. I also asked him why they even sell 3/8" fittings. He said it is mainly for supply lines to faucets and the like.
I'm going to have to read through the email materials he offered to send. If I really can't get away with a 40' run to my kitchen faucet (and a separate one for the dishwasher), I must know now.
3/8 dropping pressure more than 1/2 is simply foreign to the laws of physics. If a closed system has a pressure of 65 lbs, the WHOLE system has that pressure. It is not different further from the supply end. Cannotr be.But flow can and is reduced. That is a common misunderstanding - confusing pressure and flow. he either mis-stated it or you mis-heard him. On the inside of a cylinder thru which fluids flow, there are relationships between the walls of the cylinder and the fluid. variables are fluid density, cross section of the cylinder, surface area of circumference, temperature, and pressure.Basically in the simplest form, the walls of the pipe slow flow down by friction. A smaller diameter has a larger percentage of wall surface creating friction to slow the movement of the fluid in volumne, relative to a larger diameter, percentage wise.But it doesn't matter if you have a 1" pipe or a 1/4" pipe, the pressure will remain the same throughout for all practical purposes.
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"But it doesn't matter if you have a 1" pipe or a 1/4" pipe, the pressure will remain the same throughout for all practical purposes."That is only for STATIC pressure, the pressure when there is no flow.As you have flow there is friction drop in the lines. So the pressure at the far is is the static pressure less the friction loss for that flow rate. And it also affected by elevation changes.Here is a Zurn installation guide.http://www.zurn.com/operations/pexrh/pdfs/installation/PEXDesApplGuide.pdf"Where possible, we recommend the use of 3/8" tubing. The smaller tubing
means hot water arrives at the fixture faster and the smaller tubing can
make smaller bends. With the reduced water usage of most sink and
lavatory faucets and showers (typically 2.0 GPM), 3/8" tube is usually
adequate unless the distance to be covered is more than 80 feet. The
pressure loss information for 3/8" and 1/2" CTS tube is listed below."And for 3/8's it has the following pressure drop PER 100 FT.1 gpm, 6.8 psi
2 gpm, 24.8 psi
3 gpm, 52.4 psiAnd another source I had 4 gpm at 90 psi drop.So for all practical purpose 3/8's is limited to something like 1.5 gpm.Here is another guide.http://plomberie.per.free.fr/Documents/PPFA%202002%20PEX%20Installation%20Handbook.pdfI suggest that the OP look at both of them. Lots of details on properly installing pex..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
That's pretty much what I was thinking, it was '3 psi per ?? ft'. In my world, we discuss pressure drop per 100 ft of pipe, and it's always a function of flow. No flow, no pressure drop.
At x gpm, you'll have a pressure drop of y psi; at 2x gpm, you might have a pressure drop of 4y psi. And if you're trying to pump 5000 gpm for a mile and a half, you might have a couple of hundred psi drop.
So what would you think of running hot water to the kitchen in 3/8" PEX with about a 40-45' run? That's the one I'd most like to use 3/8" on to reduce the hot water wait time (and wasted water).
One shower would only be about 15-20' from the manifold, so I'm guessing I could get away with 3/8" for it, too. Of course, being that close, the wait time is less of an issue.
This rep also told me a couple of other things. When I mentioned that I had bought my Aquapex from pexsupply.com and intend to buy my fittings and tool from them, the rep suggested I buy from one of Uponor's authorized sellers. He said pexsupply.com is not an authorized seller. In fact, he said that Uponor doesn't even know where pexsupply.com is getting their product to sell it.
The Uponor rep (knowing that I am just a homeowner) said that if I were to buy from an authorized reseller, they would likely be willing to come out and train me how to make the connections so that I could become certified. If I did that, he said, the installation would be guaranteed by them. I asked him if that guarantee didn't merely cover replacement of the lines and fittings, and he said, no, that it covered damage caused by leaks.
This also didn't sound right to me. I didn't think any of the PEX companies guaranteed their product to the point of covering damage by the water that could leak out in the event of a failure.
One last thing that he told me is that he recommends the Uponor ProPEX EP plastic fittings over their ProPEX brass fittings. He said something about them being less subject to corrosion.
Edited 8/19/2008 10:54 pm ET by JDLee
You try looking on their website and see what they have posted for a warantee and about their certified installer program.I would get a gallon jug or bucket and see how much water flow you have in the kitchen or a similar kitchen now.I think that it 3/8's will be OK.But definity not for a shower. IIRC the water savers heads are rated for 2.4 and if you get (make) a high flow head and/or have multiple heads that it won't be satisfactory.And even the one 2.4 head will probably not flow well..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I guess I'll give up on 3/8" at the shower. It's such a short run that the wait time isn't much of an issue, anyway.
Two things the rep definitely was right about were Uponor not favoring homerun systems and 3/8" lines. All of the literature he sent proves that out. I just don't know why they'd have such different opinions on these counts.
Warranty used to be anything damaged was covered for at least 25 years.
'...I'd most like to use 3/8" on to reduce the hot water wait time (and wasted water)."Velocity with 1/2" will be greater than with 3/8", so wait time will be a little less with 1/2" pipe, not longer. Wasted water would be 78% more because the volume of water in a 1/2" pipe is 78% greater than of a 3/8" pipe.BruceT
"Velocity with 1/2" will be greater than with 3/8", so wait time will be a little less with 1/2" pipe, not longer."What.For any given flow rate the veloicty will be less with the larger pipe.But really veloicty is really not what you want to look at."Wasted water would be 78% more because the volume of water in a 1/2" pipe is 78% greater than of a 3/8" pipe."It is flow rate and storage capacity of the pipe.the flow rate is going to be restricted by the faucet..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
"For any given flow rate the veloicity will be less with the larger pipe."Yes, but flow rate in GPM through 1/2" pipe will be twice as much as through 3/8" pipe, according to the Pex chart in post 108596.12, while cross section is only 78% greater; they show 33fps for 3/8" vs 36fps for 1/2". "the flow rate is going to be restricted by the faucet."Oops. I think you may have me there. Since all of the faucets I have installed have 1/2" connections, I was thinking that they were 1/2" diameter, but I actually the connections are bigger than the last 12" of copper tubing to the faucet. If the faucet restricts flow below 2GPM, then that may undo much of the flow rate advantage of the larger pipe.
BruceT
Faucets are a strange setup.The connection on the bottom of th faucet is 1/2".But all modern installations use a 3/8" riser off of a 3/8" stop valve. And the old compression ones did not have much area.And the single lever faucets have the 1/2" threaded end connected to 3/8" copper tubing.Not sure of the internal water paths on different models.But look at the seals for Delta's. I have not measured the area, but it can't be more than 1/4" dia..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Apparently the 3/8" supply tubes and small internal orifices of kitchen faucets do not restrict flow rate much. I found the following at http://www.hometips.com/cs-protected/guides/faucets.html"For water conservation, all new faucets are now mandated to deliver no more than 2.5 gallons per minute; some provide additional adjustable flow rate restrictors."Googled Kohler faucets and found almost all listed at 2.2gpm.
http://www.google.com/search?hl=en&safe=off&client=firefox-a&channel=s&rls=org.mozilla%3Aen-US%3Aofficial&hs=Lhd&q=kohler+kitchen+faucet+flow+rate&btnG=SearchSo, since faucets do not limit water flow to less than 2gpm, I go back to my earlier statement that 1/2" pipe will flush out the cold water in the hot line about 12% faster than 3/8", but will waste 78% more water doing it.
BruceT
Thanks to everyone for the posts. What that guy was saying to me didn't sound right, and the common sense arguments you make are logical. I also received the Uponor materials he promised me, and here are a couple of charts that I think agree with what you are saying.
I don't know enough about science and math to have argued the matter with the rep (heck, I don't even know exactly what the first chart shows), but I assure you he said it would drop 3 psi per foot. From the materials he emailed me and the other info posted here, he was obviously wrong.
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Psi per ft just tells you how much head or "Oomph" the water loses as it flows. It's like voltage drop in a long extesion cord (if you like electrical comparisons). You can see tht it's small. That's because the flow rate is low. Double the flow and the pressure drop quadruples.View Image
Hi Mike--
I do understand that there is voltage drop in long runs of wire, and that it is lessened by thicker wire. And I can see the analogy. But I have to admit that there is much I don't understand about electricity and plumbing.
It seems to me that whatever water is going in one end of a PEX (or copper) line must come out the other. I guess what all of this boils down to is that if the line is long enough, it will create enough resistance that less water will flow into the line at a given PSI. Which means, I surmise, that you'd have to increase the pressure to the line to get the same amount of water at the other end?
Think about raising the height of the tank higher and you'll see that the pump eventually can't pump the water any higher. This is the "shut off head' of the pump.
Head is sometimes quoted in "feet" of water. 1 psi= aprox 2 ft of water head.
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In the Habitat house I just helped plumb, we used Uponer and used 3/4 up to manifold and then 1/2 for home runs. Seems to work great.
The reason he doesn't recommend homeruns was expained to me thus... if you home run a bathroom sink, toilet, shower, you may waste hot water. To get hot water to the sink, you need to run the water until the hot comes out, then when you run hot water to the tub, you need to do the same thing. if you had a manifold in the bathroom, you would only have to fill pex with hot water once. It makes sense.
I use Pexsupply for my purchases too. The reason...plumbing wholesalers will not sell to me as a homeowner. (I was certified for Propex by a plumber/client)You get out of life what you put into it......minus taxes.
Marv
Mike-
You lost me. I don't know what that diagram depicts or what tank you're talking about.
Wouldnt reducing the pipe size increase pressure?
Family.....They're always there when they need you.
Pressure drop, not pressure. Pressure drop goes up as pipe size goes down. Not a big deal in heating systems.View Image
The pressure drop under flow conditions is caused by the friction at the boundary of the water and the pipe wall.
The friction is related to: the velocity of the flow. And, for a given flow, or Q, the velocity is found by the equation, Q=v*a, which can be rewritten as, v=Q/a.
The area is pi times the radius squared, so if you double the diameter of the tube, the area is 4 times what it was, and the velocity of the flow drops to 1/4 of what it was.
The tricky part is you now have to move 4 times as much water to get the hot water to the fixture.
You don't mention a loop system as one of your options. I would never build a home for myself and not install a hot water loop.
Mine works perfectly just by the natural flow of the hot water. I have a large single story home and there is instant hot water at every fixture in the house...no pumps!
If you really want to do it right the 1st time....that's what you should do!
I can see the benefit of a loop system, and I believe that is what Uponor recommends (a loop system to several smaller hot water manifolds; not to each fixture). I think he even mentioned motion detectors you can install to trigger the system.
Recirculating systems seem wasteful to me. I'm sure you insulate the hot water tubing, and maybe that does away with most of the heat loss. And I guess you're saying you don't need a pump, so that saves on electricity. But I go most of the day without using hot water. If I'm just going to wash my hands or something, I'm not going to use hot water. Maybe I'm overestimating the heat loss with a loop system.
When is a pump necessary? I thought maybe you need one to force the hot water back into the water heater.
Those convection loop systems were somewhat popular in older homes ... until the 70s when energy people said they were evil. They do lose a lot of heat from the pipes, sort of the opposite thinking from the heat trap you put on the water heater. In the winter it might be a wash but in the summer it is a pretty big energy waster. You lose the heat from the water heater plus the AC to get that out of the house.
BoJangles -Have you ever done a rough calculation of how much extra your water heating costs are as a result of having the hot water loop? As energy costs continue to climb, it might not be insignificant.
I have a 3500 sq. ft. home with 4 bathrooms, a laundry room, a utility room, and 2 kitchen sinks. I have instant hot water at every location.
I have a Marathon electric water heater, 3 refrigerators and freezers, a big shop, a big garage with lots of equipment and a wife who cooks and bakes for us and most of the neighbors. We are all electric, except for the natural gas boiler.
The most I have ever paid for electricity in a month is $135, so heat loss in my loop system is not an issue to me.
If you have all of the pipes well insulated, I think the heat loss is negligable. If you don't have a loop, you will waste a lot of water just waiting for the hot water to get to the faucets. This will also add to your sewer charge if you are on city sewer. So you actually have three losses to consider...the cost of wasted water, the cost of heating the water you wasted, and the added sewer charge.
Frankly, I don't care if it cost me a few more $ a month. It is so nice to have instant hot water at a faucet that I wouldn't go without a setup like I've got.
Every time someone uses our sinks, they comment on how nice it is to have that instant hot water and they wish they had it!
I think the biggest consideration is to have a very well insulated and efficient water heater and a well insulated piping system.
Bojangles--
Your house is almost twice the size of mine. I'm guessing that with a house that size, you might have quite a few people living there. Those are both factors that seem to argue in favor of a recirculating system.
Not only is my house smaller (3 bedroom, 2.5 bath), other than the kitchen runs, all of my hot water runs will be very close to the manifold. I also live alone (although my mother may need to live with me as she grows older).
Probably the best argument in favor of a recirculating system for me is the water savings. Water is becoming more and more of an issue in San Diego. But the 3/8" runs to the kitchen and the proximity of the manifold to all of the bathrooms should give me enough savings without having to go the recirculating route. I also really like the idea of limiting the number of fittings.
Personally I find even 1/2" pex to give marginal flow rates in some circumstances. It has to do with the inside diameter of the fittings, and a discussed above the length of the run.
Besides, you are gonna have to buy a roll of 1/2" pex right? Probably 250'. So what, you gonna buy another roll of 3/8" too? I don't know... Maybe Home Cheepo sells 100' rolls?
JDLee,
I recently finished my own home and used the Mana-Bloc system with home runs that you are describing. The local Vanguard rep is a family friend and helped me lay out the runs. I used 1/2" for the tubs, shower, washer and hose bibs. The flow rate at the 1/2" fixtures is approx. 3 1/2 gallons per minute. The sinks and other fixtures on the 3/8" lines average approx. 1 1/2 gallons per minute. I placed the mana-bloc in a central location in the basement as the baths are at separate ends of the house. This makes my longest runs approx. 30 feet and pressure drop doesn't seem to be a problem for either the 1/2" or 3/8" runs. Hope this helps.
Thanks for the info. Did you run a 3/8" line to kitchen sink hot tap, and a separate 3/8" hot to your dishwasher?
JDLee,
Yes, the dishwasher is on a separate 3/8" home run to the manifold. As a side note, I considered running supply line to each area and then tees to each fixture. Of course the draw back is that each connection is a potential source of a leak, the fittings are not particularly cheap, and you lose the advantage of having a centralized shut off instead of shut offs at each location.
I might get some flak for this but I think having water "flow" fast out most faucets is stupid.
I have two teenage daughters that use water like it is nothing. So I've thought about how to reduce the water usage in our house.
When they turn on a faucets it goes on full open. With one handle valves it goes on full open With hot water mixed in. That's because the handle almost always stays in the middle.
So how do you reduce water usage in a household with people (most) that aren't aware?
Reduce the flow. Take it out of their hands.
I think 3/8" will be fine for most applications. Toilets? You bet. Lavatories? Same thing.
I also would look at two handle faucets. Most of the time all you need it cold water.
With a two handle faucet people are more likely to just turn on the cold side to wash their hands. Besides, with a single handle faucet you are just warming the pipes most of the time. Home runs or not.
My opinions aside. You can figure this out. In a bathroom you want good flow to the shower/tub. Everything else doesn't need a lot of flow.
In the kitchen the faucet should have good flow. If it gets busy during cooking or cleanup you want good flow.
Outside spigots should have good flow. You get the idea.
Just finished water lines in my son's two story house, ran 3/4" lines to a Upinor manifold in each location (master bath, kids bath and laundry room, kitchen and guest bath) and then 1/2" to the fixtures except the master suite spa which I ran 3/4". System has 68psi on the second floor. Minimize the wait for hot water with the Upinor hot water recirc pump and timer, no need to run extra lines, add the mix valve at the longest run and set the timer.
A small suggestion - try it out. Cut a length of pex the same length as you already have in your wall. Hook on end intoyour supply, the other end to the faucet you plan to use. The faucet is lying on a towel in the yard. Turn the water on and see how the flow is. You can even se how long it takes the water to get hot. You can do the same with all the fixtures you are worried about, with the lengths of pex that would be run. You're only out the cost of a crimped connector.
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Save the Whales! and Guns!
Sorry for the late post but I have been offline a bit lately.
I have been living with a vanguard (now viega or something ) pex manabloc system for 8 years.
3/8" to all the vanities and toilets, 1/2" to showers and tubs (the rep told me 8 years ago that the pressure balance systems can have some issues with 3/8 running to them (why I remember that I dont know))
I ran 3/4" to the water heater and out to the bloc and from the well to the block on the cold side.
I can regulate the pressure on my well and have no complaints at 70 psi and 60 psi is pretty aok too.
I have nice runs in the house too, not short.
fyi