We have an old house and when we replaced the hot air furnace with a new one, we had the contractor install a duct up thru the first floor to the second floor to get some heat to the second floor.
We have the duct framed out, ready to hang drywall. Before that is completed, we wanted to put some type of insulation around the duct where it passes through the floor. The floor is 1" thick oak with approx. 1" layer of concrete on top which was done to make a smooth surface to apply floor tile.