Abstract: A seal for covering or blocking airflow through a gap between a boot can and an access opening formed in a dry wall of a vent is disclosed. The seal may define inner and outer perimeter wherein the inner perimeter is disposable inside of a front edge of the boot can. The outer perimeter of the seal is disposable outside of an inner perimeter of an access opening formed in the drywall for the boot can. The seal may be compressible and have a thickness so that when an air register is mounted to the wall, floor or ceiling, the seal is pressed against (1) a backside of a border of the air register and (2) the front edge of the boot can and exterior surface of the wall, floor or ceiling to prevent flow of air between a room to be heated/cooled and an attic behind the boot can. Particulate matter in the attic is not disturbed when forced air is flowing through the system. Also, particulate matter from the attic is not blown into the room when the HVAC system is turned off.