How to retrofit hydronic heating?

Looking for an idea to retrofit hydronic heating into a room in the Winnipeg area.

Assuming:

- existing flooring removed down to clean / prepped subfloor

- 5/8 tubing, 8" spacing

- stamped (not extruded) heat spreader plates

- 156 sq foot room (12x13)

- tubing pops down through floor into basement or crawlspace and is 30 feet to the manifolds

- tubing pressure tested and hooked to manifold

Nothing else. Just basically lay the wood, plates and tubing.

See pic for sample install.

On a side note, what about a thermal break between the existing sub floor and the new laid above? Some sort of 1/8 thermal pad? Not sure if such a thing exists or if worthwhile, but it seems to make sense to keep as much heat on top as possible. No real point in sending heat down? (Thermal mass can change some characteristics I suppose)

This could possibly be over a heated basement or an unheated crawl space.

I do not want to do an electric cable type of install as I want the option of using alternate fuel sources to heat the fluid. (Such as wood, Gas, Geo, Solar, etc)