Re signed up on another year of membership Membership Re designed partial duct replacement, connecting to plenum directly. This would be running a duct from the plenum to the new silver ducts and reconnecting it all. 8†from plenum, new 8†start collar, and 8-6-6;wye, 1 8â€duct. And added register in bathroom so cat doesn’t fall into duct again. Tested system much better airflow. Clients happy with airflow