heating the floor
Well so far what I am using is - well - nothing.
HOWEVER long range (like maybe next year?) plans call for a small, hi-efficiency natural-gas fired boiler, with pumps, an expansion tank, valves, manifolds to distribute the hot water among the various loops, and manifolds to collect the cooler return water for it go back into the boiler. Valves to regulate how much hot water goes through each loop, etc. An Air/water separator is crucial.
The system is full of a 50/50 mix of Prestone automotive anti-freeze and water, and pressure-tested to 175 lb BEFORE I poured the concrete - leaks are never a good plan INSIDE the slab!