I'm trying to decide whether to install a manifold system with my new pex plumbing and can't decide whether I should go with the manifold or just rely on the shut-off valves for each fixture. Is the manifold really worth the money or is it something designed to make the plumber's job easier?

The manifold will be more efficient, and save you the money of buying and labor costs to install individual shut off valves. If you build your own "manifold system" using T's and quads, you'll likely spend as much money, and not have any better system, and have a bunch more labor involved.
I recently saw a 32 port pex manifold on eBay for $189, and each line had it's own shut off valve built into the manifold.
Just my $0.02 worth.

The PEX manifolds definetly look much nicer than making one yourself. Just watch the price that you pay.

Manifold systems end up costing more in the long run, and they are a much more incovenient to use when you have to run to the manifold whenever you want to turn on or off the water at a remote location. May as well not have a manifold or terminal shut offs at the appliance and just turn off the main if that's the case.

I love PEX but do not use manifolds.

Manifolds require more pipe because 1 pipe is used for each individual supply. Piping in the typical main, branch, and riser system like conventional copper is the best use of materials even though you have more tees and ells.

Using the conevntional tee and ell system also eliminates excessive boring of joists, studs, and so forth needed will all the extra pipe used when you use a manifold.

Manifolds do NOT save money in valves because the cost of individual valves is offset by the cost of the manifold.

Of course, one could always set up a manifold system without home runs, using a combination type system whereby one manfifold valve controled an entire branch for example....

But it still leaves the incovenience of having to go to the manifold when you want to shut the water off to a particualr appliance.

PEX but no manifolds for this plumber.

The benifit of having a manifold value set up is so that you can turn off a bathroom without having to turn off the whole house. Most plumbers have ran into the famous 3/8" value problem where you go to turn off a toilet valve(or sink) and it either doesn't turn at all or doesn't turn off all the way. Sometimes you end up replacing it and it doesn't always go smooth. Having valves located in a utility room(or whatever) is a nice thing to have. Plus what if in the future someone decides to nail a picture on the wall and they hit a pipe? You can't always get a plumber right away. Having the valves make it so you can isolate the area and not have your whole house off.

The only real downside, like homebild said, is having to run seperate pipes to each faucet.

If you use a manifold system, you still need valves under each sink and toilet.

There is certainly more expense to installing a manifold system and if cost is your only concern it is a bad idea. If however, you are interested in system performance, balanced pressure-no major pressure drop say in the shower when a nearby toilet is flushed, a manifold is the way to go. You can use smaller piping to match the volume of the fixture you are supplying-even 3/8" to a 3/8 valve which will greatly speed up the time to get hot water to the fixture meaning less wasted water.

NAHB did a study showing a homerun PEX system is 20% less to install than a trunk and branch copper system with better performance. PEX is a great product and its true advantage is in a homerun(Manifold) system

I am remolding my 1946 home with 16" crawl space and am looking into PEX piping,talked with several plumbers they do not run PEX so I will probably end up running it my self. I am looking at the manifold, I also installed a tankless water heater and they strongly reccomend that the pipe running in and out for at least three feet should be copper. How does PEX connect to copper any problems?

We only use copper in areas where looks are important, or in high heat areas. You *shouldn't* need to run copper to or from the water heater. Be sure to read the directions specific to your tankless water heater. However, you can run copper near it so it looks like a neater job.

There are special adapters to connect PEX to copper. One end of the adapter is a sweat connection and the other end is a PEX connection.

If however, you are interested in system performance, balanced pressure-no major pressure drop say in the shower when a nearby toilet is flushed, a manifold is the way to go.

This is a non-issue since plumbing codes require all shower to be pressure and temperature balanced these days.

"NAHB did a study showing a homerun PEX system is 20% less to install than a trunk and branch copper system with better performance. PEX is a great product and its true advantage is in a homerun(Manifold) system.

I'd have to disagree with this since it would completely depend on the design of the home and the location of water appliances and outlets.

My personal experience with PEX has shown me that a manifold system will almost always cost more than plumbing in the typical main and branch fashion.

This message has been edited. Last edited by: homebild,

In the NAHB quote it says PEX homerun vs. copper branch, not PEX vs. PEX. So doing a PEX homerun is probably cheaper than a copper branch system. Just the labor of doing PEX instead of copper will save you a lot of money.

Adam:

Ahhh..
Thanks for correcting my misreading of the NAHB report.

Yes. PEX wins hands-down in cost versus copper.

An example:

In the house I am currently building, the 1" 100ft coil of PE (polyethylene) water service pipe I purchases was $42.

The same 1" pipe if flexible K copper was $428 in material cost alone.

If using a manifold with a tankless system, can a recirculating pump be installed at the point of use on the hot water line to eliminate running water down the drain until the hot water arrives?

The main reason that anyone would use a home run system is to save energy. Smaller pipes with no branches mean less hot water to run out at the end of the line. This reduces the time for the water to warm up and uses less energy month to month. It also helps pin point a problem if you do have a leak cause someone "nailed it". Otherwise you should not have any case for a leak unless it is at one end or the other. This makes a case for doing the cold side as well although in some houses it would make sense to run a larger line for a luxury shower where the demand is higher. Too many subs get using to one thing and are hesitant to learn something new. That is why Europe has had pex for 20 years and as simple as it is we still resisted till about 2002.

to answer your question MrMom, Yes a pump can be used. But you should install a control on this pipe at point of use that sees the hot water being delivered and shuts off pump until the temp drops down again. But if your properly sizing the pipes and you can created a convection loop within the hot water heater to the point of use, there is really no reason to use a pump, unless the houes is so big a convection loop would not work.

Remember that several codes require a loop or pump if the hot water heater is over 100 feet away from the point of use. In any regards the convection loop is much cheaper to use and install then the pump. Which uses electrical power which cost much more then the few gallons of water wasted while waiting.