Quote:

"Home run or manifold plumbing systems utilizing PEX tubing can substantially reduce water and energy consumption in a home. The home-run concept provides dedicated direct lines from the manifold to the fixtures, reducing the amount of water that must be purged from the lines to get hot water at the fixture. Direct lines can be sized to the fixture requirements, further reducing the amount of time to wait for hot water. Faster hot water delivery reduces water waste and the amount of times the water heater must cycle to supply hot water."

Also called "Cadillac" and "overkill" systems when manifolds are fitted with individual output line shutoff valves.

"When only the very best is good enough".

I have to agree with Jake on this one, that first response sounds like a bunch of hype to me.

Let us review the facts:

Both PEX and Copper provide an very good system however the aforementioned statement that a PEX homerun system saves water, Maybe it does, but then maybe just the opposite is true, depending upon the layout. Consider this, if you have a Main and Branch layout the lead time to get the hot water from the tank to the fixture will remain equal. On the other hand, if you have a manifold and home run system it is true that the smaller lines contain less water, but consider this. You go in the bathroom and turn on a faucet at the lavatory. The hot water must then travel from the water heater to the manifold and through a dedicated line to your lav, then you step to the shower and wait again as the hot water leaves the tank, travels to the manifold then up the dedicated line to your shower, and if you happen to have two lavatories and the wife turns the water on at her lav once again you wait for the water to travel from the water heater to the manifold, then through a dedicated line to her lav. If we were to realistically compute all those losses in most instances the end result would be nearly the same, if not less in a main and branch layout.

On the other hand, there is absolutely nothing in the code that would prevent us from installing a manifold and home run system with copper.

If reducing water consumption is the main concern, then the best method would be to install a Main & Branch recirculating system, which provides nearly instantaneous hot water at the fixture.

Taking this to the next level, if your desire to conserve water is based upon environmental concerns then here again a recirculating system wastes much less water however, if your concerns on saving water is based upon savings on the water bill, it is highly unlikely that either system will have any major effect because even though most municipal water suppliers do measure the exact number of cubic feet of consumption, generally they bill in blocks of 100cu.ft. One hundred cubic feet of water is approximately 600gallons and it is highly unlikely that you would waste 600gal in a month even with a long lead time to the fixtures.(Typically a 3br residential structure will average 300gal per day total consumption.)

Many will argue that PEX is cheaper than copper, but here again, that is not always true. If we install PEX in a main and branch layout then PEX defintely has the price advantage but if we install a PEX manifold and home run system we must then install a both a hot and cold dedicated line to all lavatories and the shower plus and additional dedicated cold water line to the water closet. Thus at a minimum we have 5 lines from the manifold to the bathroom whereas with a main and branch we only have i hot and 1 cold line from the main to the bathroom. Now when you consider that one PEX fixture stubout will cost nearly as much as a bag of 20 copper elbows in the end the material cost for a PEX manifold system is almost the same as a copper system.

In can be argued that the labor cost to install PEX is much less, but here again, this is not true. While it is much easier to run the PEX tubing, if the PEX is properly installed per code and manufacturers requirements PEX can ultimately involve more labor time, by example, the manufacturers installation specs state that PEX must be protected from UV light, both direct and indirect. Technically speaking, if you run PEX through an open stud bay in a basement, and if that basement has windows the you are required to cover the underside of that stud bay with a light proof material. When the manifold is wall mounted it must either be in a windowless utility room, enclosed in a cabinet or provided with a light proof membrane curtain.

Copper requires an hanger within one foot of every major change of direction and one hanger for every 48". PEX is required a hanger for every 38" and the hangers must allow movement of the tubing. In addition, all PEX runs must have an additional 10% overall length to allow for expansion and contraction. (Now ask yourself, when was the last time you saw a PEX installation that was done by the book? In my jurisdiction we have a plumbing inspector who is hell bent on insuring all PEX is by the book, in fact, he brags that he has yet to see a PEX installation that would pass on first inspection.)

For re-work PEX has the distinct advantage that it can easily be fished through walls, but then, the same can be done with roll copper.

For new construction if PEX is run in a main and branch configuration like copper the overall cost advantage certainly goes to PEX but when we consider how much more tubing is used in a manifold and home run system most plumbers will offer a PEX maifold system or a copper main and branch system for the same price.

Now in regards to angle stops at the fixtures. The codes require that all fixtures with the exception of tubs & showers must have an individual shutoff valve, which in most instances is the angle stop, however with the advent of the manifold system the valve on the manifold meets the requirement in most jurisdictions. On the other hand, some jurisdictions such as mine have ruled that the manifold valve is a Zone valve, and they still require the individual angle stops at the fixture. IMHO i would not have a fixture that does not have angle stops. Consider this, you have a minor drip from the lavatory faucet. If you have an angle stop you can easily reach under the sink and turn the water off, make the repair, then easily turn the water on again. On the other hand, if you have a manifold and no angle stop you must go to the manifold to turn the water off, and with my luck, your in an upstairs bath and the manifold is in the basement, no doubt at the opposite end of the house, so you go down two flights of stairs across the house and probably have to move bicycles, lawnmowers and who knows what to get to the manifold, then up two flights of stairs to make a simple repair, followed by another trip down the stairs to turn the water on, back up to check your work and pick up your tools. Personally I am getting too old to be running up and down the stairs all day, oh, but it does have its compensation because I am billing additional labor time for all those stairs..LOL.

It is also argued that PEX will tolerate freezing and thawing without bursting a pipe, which is truc, but on the other hand what they don't tell you is that rodents of all varieties, mice, rats, rabbits, and opossums seem to have a sweet tooth for PEX. In fact, in the last five year we have made more service calls to repair rodent damage to PEX than to repair frozen copper lines.

I wasn't going to take the time to write that much.

But I agree, if you are making home runs, that drives up the cost of PEX over a branch system. If you insulate your lines in a branch system, using one fixture get's hot water in the pipes for anything on that branch and it stays hot for a while.

Copper has come down in price - it may be reasonable now, a year ago it wasn't.

Thanks for the thorough responses.

In my current home two baths have had leaks due to poor sweating of copper joints so I thought pex/manifold might be less prone to installation error and easier to isolate a leak should one occur.

You need a new plumber, not a new method of plumbing.

Although I've had joints leak when I tested them, soldered joints aren't particularly error prone. When done properly, they are exceptionally reliable joints and are predictable.
Usually if I have a leak, it's because I had water in the line or otherwise couldn't get the joint hot quickly. I usually knew a joint would have a chance of leaking before I tested it. I can't think of instances of "good" soldered joints leaking at a later date.