Staple up radiant in-floor heat

Looking for some opinions on this. Planning to do a home build this summer, I’ll be doing the majority of the work. Looking to install staple up radiant, in climate zone 7 (very cold). All the floor joists are 19.2” O.C. TJI with 3.5” wide flanges. Anybody ever use staple up with that spacing? I know typical is 8” O.C. spacing but I’m wondering if different is desired with that floor framing system and being 19.2” O.C. ? It’s a two story house, about 280sq ft is a great room with a 20ft ceiling open to the second floor. Sits on a ICF crawl space.
On another note, I have been trying to find some ways to calculate optimal length of circuits (under 300’ for 1/2”) and determining my heat load. Any larger windows are triple pane. Walls R30, ceiling R60.
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Underfloor heating systems have to be engineered. Building it by rules of thumb is a recipe for an expensive disappointment.
Have you done a Manual J or other heat loss calculation? You need to do a room-by-room heat loss calculation and then design to meet that load.
Thank you I will start with the manual J calculation. I did pretty rough estimates but I’ll go from there and get it much more detailed.
To the question you asked, the limit on PEX spacing is usually the bending radius of the tubing being used. The smaller the tubing diameter the lower the bending radius.
If you go to the Uponor website you can download a free trial of their LoopCAD software. It's really easy to use, just plug in the values they ask you for (window sizes, wall r-value, etc) and it spits out a ManJ. Then you can select how many zones you want, press a couple of buttons, and it automatically creates the pex layout for you.