A.
Cut & install -1/2" concrete board covers for the air supply channels with a 5"- 6" overhang on both sides of the channel [concrete face down].
B.
Cut and install -1/2" concrete covers for the air register channels with a 4" overlap on both sides of the channel [concrete face down].
C.
Tape the concrete boards on the sides and at the seams with 3" duct tape to insure no movement during the slab pour.