Plumbing question: the plusses and minuses of manifolds

[MikeT]

I am fixin' to get ready to start planning my PEX plumbing effort.  What do all y'all think of using manifolds in the water distribution system?  What are their advantages and disadvantages?

Thanks,
Mike

[MountainDon]

Mike, I haven't done much looking into this myself, but what I see as advantages includes:

You can have shut offs at the manifold for any or every run.
The PEX tubes will be one piece from here to there.
Fewer fittings in the lines should equal less pressure drop at the end.
Smaller diameter tubing can be used when the line is only supplying one or two fixtures at the end.

The disadvantages I see are:
Greater amount of tubing used with resulting greater cost.

Now let's here from the plumbers.

[rdzone]

Greater tubing my result in greater cost, but have you priced pex verse copper...it is a no brainer.     I can get pex dirt cheap compared to copper.

[NM_Shooter]

I just bought some stuff today from www.pexsupply.com  take a look at their prices.

Manifolds are good for balancing flow rates throughout your design.  But I prefer to run hot water in a loop, and have a return line pump it back to the hot water or storage tank.

PEX is sweet.

-f-

[ScottA]

Manifold it Mike. No question about it that's the best way. If you have long runs you could do a couple of manifolds in different spots. Put shutoff valves on every run and make it easy to get to.

[MikeT]

For a small-average size home, is there a recommended size of manifold?   How many "taps" or whatever they are called?

3/4" or 1"  (I have really strong water pressure).

mt

[Daddymem]

One drawback is the volume of cold water you have to push through the pipes before the hot water comes.  Our second floor hot water has to run much longer than usual before it gets warm.  For us, part of that is a semi-tempered basement so yymv.

Another drawback is the number of lines up in your ceilings.  You have to plan pretty well and provide the room for multiple lines.

Love our pex system, wouldn't do copper if we had the choice again. HTH.

[ScottA]

I'm not sure what an average home is these days but 3/4" is common (2 baths). You can put as many outlets as you need on one manifold but sometimes it's easier to split it up if the house has alot of fixtures..

[NM_Shooter]

Most residential PEX runs are 1/2".  It flows much, much better than copper.  I have 1/2" lines to a shower in the far corner of my house, and it delivers all the water you would want.  I have a well that develops 50psi of static pressure.

If you manifold, you would probably run 3/4" to the manifold, and 1/2" from the manifold.  You can easily make your own manifolds using 3/4 X 3/4 X 1/2 Tees ($2 each) or if you have a cash cow, buy the manifold for $100. 

Without a hot water re-circ pump, I would manifold.  With a hot water re-circ pump, I would run a loop.  I guess it depends on your water situation.  I am on a well, and even more importantly on a septic, so using a minimal amount of water is important to me.  The original part of my home is 2200ft^2, and the hot water is plumbed in a loop using 1/2" Wirsbo.  We don't see any reduction of water pressure anywhere on the loop.

Check out www.houseneeds.com or www.pexsupply.com for their selection of PEX. 

Did I mention that I love PEX?   

[Homegrown Tomatoes]

I'm not a plumber or an expert by any means, but I think they're a nifty idea when plumbed correctly.  When polybutylene (i think that's what it is) is used, another story altogether.  About a week after we moved in, one of the valves on the manifold in our rent house blew just after midnight, and though I reached it almost immediately and got sprayed in the eyes with scalding water, three rooms were flooded in the space of about 15 seconds.  The plumber who redid the manifold put in copper pipes and compression fittings, and we've had no trouble since then.

[MountainDon]

The good thing is PB (polybutylene) is no longer used. But there's a lot of it out there already installed. PB has problems at the joints/fittings. It also doesn't take kinks, whereas PEX, if kinked, can be heated with a heat gun and it's as good as new again.

[John_C]

The manifold concept is new to me but it makes a lot of sense.

If you do put a manifold in a utility room and have a fairly long run to one of the bathrooms do you

1. do a homerun for each fixture?  You might end up with 3 cold and 2 hot runs.  If you do that do you put shut off valves at the fixtures in the bathrooms in addition to the ones at the manifold?

2 run from the manifold to the remote bathroom and branch off in a convention manner in the bathroom?

3. Other??

[glenn kangiser]

I'd say any of the above.

I have been to new apts with home runs to everything, but I used a small manifold with 4 outlets and did several room area combos with no problems.

I'm sure Scott will know what is best though.

[ScottA]

1. Normaly you would have shut offs just at the manifold.
2. You can do it either way
3. Make a second smaller manifold near the end of the long run.

Plumbers are cheap and will try to save pipe if they can do it without a lot of extra work. I usually don't put pex joints in hard to reach places so home runs tend to be easier. Manifolds can be put in closet walls with an access door so having more than one manifold isn't really a big deal. Normaly your longest run will be to the master bath so having manifolds in the master closet is a good option depending on the layout. Another advantage of the remote manifold is you only need to wait for hot water one time rather than waiting on the sink and the shower etc. I normaly will take the main cold directly to the water heater then build my manifolds in the water heater closet or mechanical room. If I have a long runs I'll make remote manifolds near those areas.

[considerations]

Scott, can you clarify the footage of a run at which point you consider it to be "long"?

[Willy]

I use a manifold system on my place. I did it for a different reason tho. I have my pressure tank in a different building in a room easy to heat. I ran a seperate 1" PVC pipe to each (3) freeze proof spicket in the yard, one to each barn and 2 to the house (one is a spare) This way if a pipe freezes, breaks or needs repair I do not loose the whole system. I also get real good flow for fire use ect at each location. In my home I ran 1" and tapped off for all the stuff and use a main shut off also at the hot water tank. I put 2 drain valves (hot & cold) in the craw space and can open the spickets in the second story and under the house and drain the whole system. I made sure when I plumbed the house the whole system was graded to allow no water left in the pipes when drained. Haven't had to use it in 13 years but if I do it is there. I do have a whole house filter system that does all the water in the home except the washer and house outside water spickets. Mark

[ScottA]

Scott, can you clarify the footage of a run at which point you consider it to be "long"?

Depends but generaly anything over about 20' away.

[considerations]

ScottA.  Thank you...

[JRR]

In a home, whether to use a loop or manifold layout is a matter of choice and convenience.

But in a large facility: (think industrial plant, shopping center, school, or church) ... a manifold layout can cause a bit of trouble.  Imagine a water fountain in such a facility, in a remote location in the facility, rarely used ... and served by manifold piping.  You probably would not want to drink from such a fountain because the water in its (long?) pipe run has become very old and stagnant.  No municipal chlorine in that water!  Such facilities are usually designed with loops (and manifolds) ... sometimes even small recirculation pumps ... that assure no potable water sits too long.

[glenn kangiser]

Good point.