Had radiant floor in stalled on my first floor about two years ago and what I’m finding is it has a hard time keeping up on the coldest New England days. Current config is 3/8 Onix stapled up. Aprox 2” air gap with foil foam and fiberglass bat.
Tried maxing the mixing valve but still don’t get much over 65.
60’s 1 ½ story cape recently renovated, new windows, doors, fully insulated.