Usually if the radiant pipes are attached to the underside of the floor than the water temperature is around 80 degrees. If you use 170 degree water then it will warp/buckle the wood floor.
I'm familiar with what you're describing, but what I saw actually had the copper lines about 4" below the sub-floor. Basically, the baseboard heat supply lines were run thru each bay parallel to the joists (one run per bay and then reverse to the next bay). The heat was contained by covering with foam board insulation. Seemed like a pretty effective and simple solution if you were just looking to do one small bathroom.
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