Manifold vs. Recirc loop

Contractor

Its a study on branch and tee copper vs. homerun pex. interesting stuff. Ill look for more. and about the 100', 100' of 3/8" holds about .5 gallons. but 100' is gonna cause a huge pressure drop and usually isnt recommended, in that situation just add a remote manifold with its own little water heater or a small recirc (3/8" maybe 1/2").

Greg T

There is a thread several steps below in the main list called, "PEX opinions". I know that this is a "Heating Help" forum but that thread started to go to a discussion of Manifold vs. Recirc loop systems and that is my interest. I didn't know if I should post in that original post or start a new one, since it was different from the original scope. I started this new one and hope that is okay.
That thread, "PEX opinions" is one of the most interesting and educational threads I've read . First off to Contractor Kevin, YES, please "post some links about studies done with 3/8" PEX in home run style installations and also about homerun vs. branch and tee." Please bear with me while I get caught up with a brief summary of these systems so far. Two valid sides are expressed with equal authoritative statements and facts. As a once retired GC who got back into the business a couple of years ago after a ten year absence, I'm thankful that the Internet is there to keep me updated with current products and practices. I've always tried to educate myself on the different trades work and practices in residential homebuilding so that I can converse, hopefully intelligently, with the individual sub. This is especially true since I have relocated to a new area and am working with subs I have no previous experience with and don't know their level of expertise. On the one hand, Kevin Pulver prefers the Recirc Loop system, while Contractor Kevin is more partial to the Manifold system. I'm more familiar from years ago with the Recirc system but want to keep an open mind about the manifold system. To make sure I'm following the systems correctly let me summarize my understanding of the Hot Water ReCirc System:

The ReCirc System: From the Hot Water Supply runs a 3/4" PEX line, insulated, in a path that goes as near to each fixture as possible. Also at this starting point is circ pump (i.e., Grundfos) with timer or temp sensor. If the house is two-story, the line would still be a continuous path that takes each fixture in sequence in relation to it "nearness" to the hot water supply and sometimes having to "split" the difference between two fixtures on different floors. At the furthest fixture from the tank would begin the "return line" which as Kevin Pulver states switches to 1/2" PEX to return to the Hot Water Supply with a "a swing check valve to the return so it can only flow one way". To feed each fixture off this 3/4" line would be a 1/2" PEX run to to a copper stub out at each fixture. This would be finished with a "1/4 turn ball valve style stop with compression fitting". Add a swing check valve to the return so it can only flow one way. I like the simple definition that this 3/4" loop system is the "holding tank" always containing the hot water as needed.

The Manifold System: this is a newer system to me and here is how I understand Contractor Kevin. From the manifold/manabloc is a "homerun" to each fixture with an indirect tank next to the manabloc. It can use a smaller 3/8" PEX delivery line.

Now, let's just just look at the farthest fixture away in a large 6,000 sf 2 story home with both systems. That fixture is about 60' from the hot water tank. By the nature of its continuous loop, the Recirc System has the hot water within several feet of the fixture at all times and would seem to provide hot water rather quickly. On the other hand, the Manifold system would have the manifold located near the hot water supply and the "home run" would have to drive about 60' of cool water out of its line before delivering the hot water. I'm anxious to see the studies Contractor Kevin is referring to so an accurate conclusion can be made.

There are a number of pros and cons sides forming up in our industry over other construction techinques. Tyvek vs. Grade D paper; Gypcrete vs. Dry Sandwich; Icynene vs. Batt Insulation; and on and on. Valid points on both sides. I really appreciate the expertise and professionalism that all sides on this issue project in their posts on this website. With new subs that I interview, it has become more important to me not their past jobs or references but almost more importantly what websites they frequent to keep up with their trade or which recent trade shows they have attended. I don't mean it as a slam but I am amazed that more of the subs I deal with don't know how to get on the Internet and their only education comes from the local supply house or a State required test.

hr

A recirc system

requires a circ, which consumes power and needs to be insulated for it's entire length to minimize loss.

The manifold systems use a small diameter tube which flushes very quickly.

The biggest mistake I see around here with recirc is NO insulation, oversized circ without timer or thermostat. And for some reason the plumbers think the recirc line needs to be 3/4"

Check out this 160 foot recirc loop fastened tightly against a concrete wall! It has the concrete foundation wall heated to 85 F!

His boss told him to do it that way was the plumbers response. A million dollar home, by the way.

hot rod

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jalcoplumb_2

My opinion.

IMO, I tend to like the manifold systems. We can split hairs all day long. First, in an insulated recirculation system you will have heat-loss. The timer is a good tool to help minimize the heat loss but it is still there. This can cause your water heater to run more often. Second, you have a pump. This uses electricity and can fail. You can set up a gravity recirculation system in some cases. This will eliminate the need for the pump but you will have more heat-loss due to the constant circulation. Third circulation depending on the flow rates can cause wear on the piping system.

Manifold with a water heater in close proximity eliminates the need for circulation. I don’t have the time to figure out how long it will take to purge a 100’ 3/8” line of cold water but I do know that it does not take long at all. What are a couple of seconds and a few pints of water when you are saving energy, time and money?

Any one out there got some free time to figure it out how long and how much water to purge the 3/8” line?

Opinions are great.
Joe

jalcoplumb_2

beat me to it.

I need to refresh more often.

hr

at 8 fps

about 12 seconds

hot rod

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jalcoplumb_2

FLIR?

What brand and model FLIR? Interested in getting one.

kevin coppinger_4

Contractor knows...

where to find the articles....FYI Contractor and I are not the same person....I just know from close to 300 installs (both PEX and Poly the benefits to me AND my customers. If done with care it can look neat.
In repipe jobs it has been a Godsend so as to not have to tear open walls and yes not add fittings. People have peace of mind and be more confident that a fitting will not leak in a wall (copper, brass,plastic or soldered)and some do sooner or later. If the wirsbo fittings are so great why not place a bunch in radiant slabs..it would give a place for all those 75' leftovers...
I 'm not saying there is not a place for recircs...just don't poopoo manifolds. kpc

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Kevin Pulver

K.C my friend

You haven't told us anything except you really like the manifolds after much experience. "look really neat if done with care." Ditto recirc loop. "Godsend in re-pipe jobs to not tear walls open." OK, So they might be easier to install if you don't have the chance to do the preferred method. Or you could probably just tee in a longer branch and do the recirc loop also. "fittings leaking in walls" Honestly, what kind of junk are we installing if we are losing sleep over the fittings springing a leak when the the lights go off? "Using up 75' pieces to do radiant" Wirsbo says you CAN put their fittings in a radiant floor, but it would be unprofessional to use up leftover scrap to fill a new slab job. "Some fittings leak sooner or later." If a Pro-Pex fitting is going to leak, it will leak NOW- because you somehow did it wrong. You'll know it and fix it. Someone above mentioned "adding a recirc loop when the manifold has to be some distance from the source." Isn't that a point for the recirc system?
I've helped install many manifolds (admittedly nowhere near 300) and they're fine. But the advantages are for the installer- not the end user- and a few bucks don't matter; in the context of a better system.

kevin coppinger_4

Well.

> You haven't told us anything except you really

> like the manifolds after much experience. "look

> really neat if done with care." Ditto recirc

> loop. "Godsend in re-pipe jobs to not tear walls

> open." OK, So they might be easier to install if

> you don't have the chance to do the preferred

> method. Or you could probably just tee in a

> longer branch and do the recirc loop also.

> "fittings leaking in walls" Honestly, what kind

> of junk are we installing if we are losing sleep

> over the fittings springing a leak when the the

> lights go off? "Using up 75' pieces to do

> radiant" Wirsbo says you CAN put their fittings

> in a radiant floor, but it would be

> unprofessional to use up leftover scrap to fill a

> new slab job. "Some fittings leak sooner or

> later." If a Pro-Pex fitting is going to leak, it

> will leak NOW- because you somehow did it wrong.

> You'll know it and fix it. Someone above

> mentioned "adding a recirc loop when the manifold

> has to be some distance from the source." Isn't

> that a point for the recirc system? I've helped

> install many manifolds (admittedly nowhere near

> 300) and they're fine. But the advantages are for

> the installer- not the end user- and a few bucks

> don't matter; in the context of a better system.





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Kevin Pulver

I took the time Joe

look on the other thread "pex opinions" and see if my figures hold water (no pun intended) Is this a great country or what? If you guys have never seen plumbing in a 3rd world ghetto, you don't know what it is. We can argue over the finest materials, methods, and systems, and standards that the world has ever seen! America Bless God!
Kevin

kevin coppinger_4

Well...

how much do I need to say? I think I have been pretty clear between the 2 threads. They work. Period. Recirc lines do too. I prefer the manabloc set up...you think it is bad bad way to go. There are plenty of adavantages to each. The recirc pump will cost more to operate and when it breakes more to replace...especially if there are water quality issues...A "few" dollars can make a differance to some. I don't exclusively install manabloc's. But they have their place.
I will give you the last word. kpc


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Kevin Pulver

Manifolds are a good system K.C.

All I'm saying is that for a guy doing new piping, especially on a new house, wanting the best system for the long haul- he better check the math that the manifold guys are selling him. Because I think their "benefits" of quicker hot water, less waste, and better pressure are absolutely facetious compared to the recirc. (compared to a non-recirc branch system they would have a better arguement) And yes, knock off a few hours of time and the pump, and you could easily save 5 to 7 hundred dollars or whatever. But that doesn't make the manifold a better system- it just makes it cheaper. Furnaces are cheaper than boilers, but that's not the philosophy of the Wall.

Chuck_17

Great subject. Two questions.
If you like the recirc vs. the manifold, would you use a manifold in a small house (say a townhouse or condo) where you would not be using recirc anyway?
In that small townhouse with a samll utility closet (no basement) will the manifold fit in the closet tucked in above the water heater?

kevin coppinger_4

Yes.

Manifolds work best in avg. to small houses.


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scott markle_2

The issue of manifold vs. recirc. has variables. For the 6000sq. ft. modern house the expectations of the final user probably dictates the use of recirculation of some sort. If any level of conservation ethic is considered occupancy sensors are the only way to go.

Relative scarcity of water, fuel and actual layout are the variables.

While it can be safely assumed that scarcity will effect both items Geography will decide which deserves preference. In The desert southwest with it's abundant solar opportunities and scarce water, recirc. should be mandatory for a larger house. In other regions It's a different story

The single family house of the future will be mindful of global economic realities. These structures will incorporate hydronic layout into the actual form of the structure, from roof orientation to room layouts that value compact plumbing arrangements. For this sort of structure manifold home run piping is the clear choice.

In my experience with smaller structures manifold 1/2'' pipe arrangements work very well, great pressure balance and reasonably short wait for hot water.

Cosmo_3

it is all application

I mentioned this in the previous thread. In normal 2.5 bathroom
houses that fall somewhere near the 3,000 sq ft mark and under I would say that the manifolds are definitely the way to go. Somehow I have been stuck doing larger homes 7,000sq ft and up. These houses only have about 55 psi to begin with as they are all fed by well pumps. In these cases, I am reluctant to start running home runs to 8 bathrooms. So I do a modified homerun/manifold systsem. I run 3/4 pex mains to a centrally located spot between bathrooms, install manifolds to run home runs to each fixture, and bring a 1/2" line back for recirc. The recircs operate off of sensors located in the bathrooms. Ideally each bathroom would have a dedicated circ but economic reality makes for one recirc pump that heats up the network whenever a bathroom is used. Still energy hog in my book even with the insulation but better than the homeowner's wish of letting the pump run 24/7!



Cosmo