HELP! Suspended slab radiant heating insulation question
We are doing hydronic radiant on both floors of a new rambler, 1900 sq ft per floor. In the basement we put down 2" foam board insulation under the tubing before pouring the slab (with the sides insulated as well), so we should be good to go on the basement level.
On the main floor the tubing is laid atop the plywood subfloor, which will be covered with 1.5" gypcrete (suspended slab). The question is, do I need to insulate between the floor joists below the subfloor even though the basement level is also heated? I assume every bit of insulation helps, but from a cost/performance standpoint, would filling between the floor joists with fiberglass batting make enough of a difference to pay for itself, or would the improvement be minimal?
If this were a staple-up installation this would be a no-brainer, but with a suspended slab above a heated basement I didn't know if the in-floor insulation would be cost-effective. Any advice appreciated!