Re: pex plumbing system with new home construction
If you search these boards, you'll find plenty of debate on PEX vs. copper, so I won't get into THAT here.
A manifold system will likely result in hot water getting to remote fixtures FASTER than a trunk/branch system, since the total volume of cold water that must be evacuated from the line is less since there are smaller pipes involved. However, in a trunk/branch system if one fixture recently used hot water, another fixture will receive it sooner since there is already some amount of hot water in the line.
In a true trunk/branch system, you would have a single trunk line that gets progressively smaller as fixtures are tapped off of it. The trunk goes by each fixture, resulting in a relatively short line from the trunk to the fixture. In reality, most installations actually have branches off of branches.
Implementing a recirculating system becomes much more difficult with a home-run manifold system than a trunk/branch system, as there is a "dead end" on each line that must be dealt with. The easy way to deal with this is to use a thermostatic valve at each fixture, redirecting the cooled water from the hot line back into the cold line, and having a recirc pump on the water heater.
A recirc system on a trunk/branch system can be done the same way, or you can simply run a return line from the farthest fixture back to the water heater, where a recirc pump pumps it back into the cold supply at the WH. This is simplest with a true branch system; otherwise you would have to install multiple return lines and thermostatic valves.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.