Secure Flex Vertical Firestop

If there is living space above the ceiling level, the firestop/spacer must be installed on the bottom side of the ceiling. If attic space is above the ceiling, the firestop/spacer must be installed on the top side of the joist. 

This venting component is used on some Astria, Superior, and Lennox gas burning direct vent fireplaces.

Check your model's Installation Manual for listed Secure Vent Components.