This outside air kit mounts to the intake on the back of the insert to provide a sealed docking point for a 3" intake air connection to be run up the chimney. This intake requires additional venting with proper Colinear 3x4 Stainless Termination in masonry applications or a colinear thimble for zero-clearance applications.
Note: The Accentra Insert was discontinued in 2012 and became the Accentra 52i, which uses a different outside air assembly. If you aren't sure which model you have, your model number is listed behind the right-side cast panel door.