Help with pex routing for underfloor install

mustangous

Its been 3 years since I installed radiant heat and I've been very happy thanks to the help of this board!
Link to the first floor thread... forum.heatinghelp.com/discussion/148083/ideal-pex-routing-for-underfloor-install#latest

Hope someone can help me out about routing the pex for underfloor/joist bay installation for my second floor and let me know if im the right track or what can i do to make things better and more efficient.

I am getting ready to run 1/2 pex on 8" centers with heat transfer plates. Before I do so I am trying to layout and calculate all loop lengths on paper first. So when i start, I can just get to work..

Long story short as possible...
We did an add-a-level addition and Im trying to figure out the best routing for pex for underfloor radiant heat. I have a few obstacles and not sure how to route my pex tubing to over come them. The way the second floor was designed and built makes for a tough install for consistent loop length with minimal bends.

Construction.... My house was originally a full brick ranch built in the late 50's. The architect designed the second floor in a way that the gable end sits on the existing brick so it wont look like an addition when the second floor is sided and butted up to the existing brick. In order to do so, he had the floor joist on that outside wall turned perpendicular to all the other floor joists so they all sit on the brick and outside wall. I had all the rim joist sprayed with closed cell foam and each of these bays are only 23-24" long and on 16" centers. After you see the pictures below it will make a little more sense... Definitely not an ideal situation for underfloor pex and a lot of bends.

The current plan, I am going with 2 zones for the second floor. Zone 1 for the Master bedroom and bathrooms. Zone 2 for the rest of the second floor. Zone 2 is more straight forward. Zone 1 has me a little confused because of the perpendicular joists..

Attached are what im thinking. Most of the details are on the photos: zones, loop routing, loop lengths and roughly where the manifold is. I have very little options for the placement of the manifolds and pex for running back to the basement because most of the first floor is an open floor plan.

There are 2 photos and the only difference is in loop lengths for zone 1. I'm not really sure on how to approach that because of all the bends. I already have all the 1/2 pex, but would 3/8" pex be better for that zone because of the loop length and the bends? I am trying to keep everything as even as possible.

Any suggestion would be very much appreciated!