[Cbbingle]

I am very grateful to have found this site. There appears to be many years of knowledge available as a resource for information. Once again for that I am grateful. Here is my situation.

My wife and I just purchased a 4265 sq ft home that is basically a shell. It needs all new plumbing, electrical, and all finish work. I plan on having a PEX system with a main manifold with lines running directly to each device. For the showers and 6ft jacuzzi tubs I would like to stay with 3/4 for pressure reasons, but it looks like many people are suing 1/2 in with no problems.
The system is on a well so I will need a softner, I am also using three tankless hot water heaters, one for each floor.
I am trying to figure out the design and what order things need to go in.
If I should have a separate manifold for each floor and the water heater for that floor by itself or if all floors can come off one mainfold with the three heaters backing it up?
Line coming into the softner, then into the heaters, then into the manifolds. This would be for the hot, for the cold into the softner and directly into the manifold?? This is the situation I am faced with, any and all suggestions would be greatly appreciated!