Ditto coffeehaus' statement re acidity and pin-hole leaks. I had that problem in MD and slowly replaced the copper with CPVC with glue & compression fittings. CPVC is a good product but PEX has become the product of choice. PEX-to-PEX fittings are crimped on and there are solderless fittings for PEX to copper & CPVC. Also, plumbing PEX is different than radiant heat PEX. I like the idea of ON/OFF control at the main feed. A manifold is required if tubing is run individually to each fixture (homerun method as shown in pic above) or connections are made using a hybrid of homerun and branch feeds. I would also plan for a little more distance from the electrical panel. I have not heard of any problems with mice chewing plastic lines and I live in the Adirondacks where there are lots of seasonal homes and summer camps.

When things aren't sold in a huge variety the reason is usually because the trades involved assemble their own stuff to match each job requirement. Transitions custom made for each new flooring installation by the people on the job are another example.

Yes, you can run 1" to the water heater and make the split as you describe, however, before you do anything towards desiging your PEX system I would strongly advise you to download a free copy of the PPFS (Plastic Pipe & Fitting Assoc) PEX Installation Manual. The manual is a free download in PDF format and it will not only answer your immediate question, it will give you all the tables and design parameters to correctly design your system. http://www.ppfahome.org/pdf/PEX%20Handbook_draft_rev_2008.pdf

I'm afraid I wasn't clear enough with my manifold query and it led you to misread what I was thinking of doing... Allow me to clarify. I'm not planning to use both the 1" inlet and 3/4" outlet of the manifold as inlets. I may use the 3/4" outlet as the inlet and the 1" inlet as the outlet to continue a 1" trunk line. I'll be reversing the flow of its advertised direction. When I checked with Uponor, they told me that it was designed to be used with the 1" as the inlet and 3/4" as the outlet so it wasn't *recommended* in reverse. They didn't endorse what I'm contemplating, but other than toeing the company line and stating that it's "not recommended," they didn't believe there would an issue. But the tech didn't know if there were fins/spoilers/baffles/pitches/etc. in the interior of the manifold or the ports that were engineered with water flowing in the recommended direction. I don't believe there'll be an issue, but I was hoping to get a confirmation from an actual application. As to the continuing 1" line that's downstream from the manifold, I can't foresee any issues to subsequent flow-through, inline manifolds along the way and their 1/2" ports, but I'm not absolutely certain since the velocity would slow going from 3/4" to 1". I was hoping to get some opinions and real-world experiences on that, too. Between the additional volume in the 1" compared to the 3/4" and unlikelihood of having more than three fixtures on those 1/2" lines being used simultaneously, I don't anticipate exceeding the supply rate of the 3/4", so, in my mind, I'm thinking that I shouldn't have any pressure balancing issues either with the 1". I agree that the less pex I run, the better. So other than the 1" or 3/4" question from the above paragraphs, I'm set on one "continuous" trunk for COLD with several, inline, multi-port manifolds along the way with 1/2" lines to the fixtures. My hall bathroom, powder room, and laundry room are clustered together so that minimizes excessive 1/2" runs. The master bathroom and kitchen are to the back, far-left and back, far-right, respectively, from the longitudinal center of the house, so I can't escape having some semi-long 1/2" lines to the kitchen unless I tee a 1" or 3/4" branch line, which I'm not inclined to do. For the HOT, I'm still leaning toward 1/2" homerun lines, especially for the master bathroom and kitchen, to minimize wait times and residual waste. I ***may*** do a 3/4" line to the central cluster and use a local manifold set-up to minimize 1/2" spaghettification: it's still under advisement. What's your opinion on pressure balancing loops? It's like the chupacabra; some say yes and others say no. I'm trying to figure out if I should(n"t) for the HOT's multi-manifold set-up. My inclination is to loop it since it can't hurt, unless there are specific cons against it. Thanx for your response, Vith. I was beginning to worry that my query would suffer a slow and virginal demise. J