Insulating Radiant PEX Tubes between joists under 1st floor

harraseeket

PEX tubing looped between joists with access in cellar and radiantly heating first floor. Aluminum plates fixed over the PEX. Need to insulate under the tubes/plates as significant heat stays or radiates into the cellar (my workshop). Winter temps 1st floor at 70 degrees, but cellar is MUCH warmer. The joists have cross struts to stabilize. Can I install rockwool batts, cutting around struts in joists, and use metal springs to hold in place? Batts installed to touch the plates/sublfloor with no space. We just want to transfer more heat to the floor above, even if we do not 100% seal the joists/struts. Our radiant was backfit to replace original (CA 1950) hot water tubes/fins around the ist floor.

Alan (California Radiant) Forbes

Rockwool is a step above fiberglass insulation - it also costs more. It''s also better for sound insulation.

You'll get different opinions on where to place it, but I always push it all the way up to the the subfloor if using plates as plates heat by conduction and insulation contact won't interfere.

If you were to use something like Ultra-Fin which needs an air space for convection, keep the insulation 2" away from the Ultra-Fin to allow for convection currents for heat migration.