What's the winter temperature swings like there? I lived in Hammond, LA for 15 years. During the winter I worried about wearing out the thermostat switching it back and forth between heat and cool!! :-) At least it seemed like it. If NC coast is anything like that I would be skeptical about radiant working like you would want it too because you would want to go from heat to cool in fairly short order and fairly often. You need a system with fast response for that. Radiant, particularly if you put into concrete slab, is a slow response system. That's the only issue I can see at this point.

I think you can do radiant heating with a heat pump . I guess it would be a desupper heater / water to water unit. Or have I misunderstood?

oops NM, concrete is poured allready

Currently live in upstate NY in stick built with forced air for heat. No living experience in NC.  Coastal NC appears to have 3 months in the 30's at night requiring heat with day temps in the 50's.  Not sure if that constitutes fluctuations in temp.  But was under the impression that ICF structure mediates temp fluctuations.  Is that correct?  Have pretty much decided to incorporate RH in building the ICF house in NC since AC is the most important and would rather be able to separate the systems to place vents near ceiling to maximize efficiency for air and during months requiring heat to be comfortable as well.  Is this logical?  So would a heat pump provided cooling as well as heating for the RH?  Or would a boiler or water heater be more appropriate for the heating supply for the RH and then a strict air conditioner for cooling.  Looking for advice.  Thanks

I like radiant heat but honestly a heat pump with forced air sounds perfect for your area. Wiith such small need for heating I can't imagine spending the $ for radiant when your heatpump should provide plenty of heat. I don't think the high location of your registers (optimized for A/C) would cause a problem when you need to heat in such a mild climate.