Radiant Ceiling Under Heated Floor -Advice Appreciated

hullabaloo

I’m leaning towards heating the ceilings on two levels of my split level home (basement and garden level). Aside from manufactured products (Messana etc.) I’m not seeing as much info online as I would expect. I’m hoping to build the system with thin gauge heat transfer plates, and preserve the sparse head room on these levels by recessing them between the joists rather than across them. There are already heat plates on the subfloor above the radiant ceiling. I used LoopCAD for the floor design, but they don’t have a ceiling specific tool.
Questions:
1. Would I reduce/eliminate the amount of insulation under the top plates if the bottom plates will likely be heated at the same time?
2. Does anyone have a lead on calculating Btu output of 5” wide stamped heat transfer plates, covered by 1/2” sheetrock? Compounding this equation is that the joist bays will already be warmed by the heat plates above. The room with the highest heat requirement is 18.6 Btu/hr/sq ft (a small corner bath with an older garden window), but most of the rest of the rooms on the garden level need around 9.5/sq ft. I’m hoping to make this work with the same 120 degree water temps that my floors use, and adjust plate spacing to avoid excessive cycling.

Zman

I am working on a retrofit system design for a property with failing Entran tubing as we speak.
I think your sketch will have some "constructability" issues. I can't see how you will get the bottom assembly put together in a secure noise free manor.
I am looking to do a system something like this https://www.pmmag.com/articles/101670-john-siegenthaler-radiant-panel-systems.
Pex-Al-Pex is a good idea to help reduce expansion noise.
You should have no trouble with heat output.

hullabaloo

Thanks Zman,
I hadn't thought much about noise in the ceiling, but I'm using the same plates under the subfloor and the reviews are really good and I saw no noise complaints. I was thinking of ripping thin strips of OSB to sit on each side of the pex channel, then cross another strip on top of that to hold it until the drywall is in place. I was thinking that two braces per 4' plate would be enough, but perhaps when the pex is filled it would sag.

Regarding your article; That's great information, I'd not seen that before. I'd seen an under-OSB/drywall setup like he depitcs, and it certainly is a sturdier set-up. I'm loathe to lose the 1.25" of headroom in our barely 7' basement, but it may be worth it in the end.