radiant slab floor suspended over basement
My husband and I are working on a design for a energy effecient home in NW Arkansas. We have long mild springs and falls with freezing temperatures and snow in the winter and a couple of months of very high temperatures in the summer.The site is heavily wooded with deciduous trees which will be benificial for the shade in summer but since it is on a south facing slope we will be able to take advantage of passive solar heat gain in the winter. We would like a finished concrete slab floor with radiant heat over a walk out basement. The concrete slab will serve as our passive solar heat storage while the radiant heat will serve as a backup and to even out the temperatures for cloudy days. The house will be around 2500 sq feet including the basement. The basement will serve mostly as storage and as a utility area but will have radiant heat in the slab also. We are planning to use ICFs for the basement walls and SIPs for the roof and possibly the perimeter walls.
My questions are: do we need to insulate the under side of the suspended concrete slab (basement ceiling) to keep the upstairs floor warm since it is over the basement?
What is the best way to heat our slab in our relativly mild climate? Tankless water heater? Hybrid? We have considered an outdoor wood boiler since we have an unlimited supply of wood but they are expensive and we would have to have a backup system for when we are out of town.