Snap-Lock Black Steel Stovepipe 6-Inch Male to 5-Inch Female Reducer

In all likelihood, the collar of the side of the insert is for outside air and this cannot be used to vent the insert, however, there will be two ways to accomplish the goal of passing through the damper without affecting the damper's integrity. One solution would be to ovalize 6" round flexible chimney liner allowing it to pass through the damper and connect to the insert. A better and more simple solution would be to connect a HomeSaver Small Ovalflex Adaptor (Straight/round on top to Ovalflex on bottom) to the end of the flexible liner before dropping the 6" liner down the flue. The ovalized portion could safely pass through the damper and connect to a HomeSaver Small Ovalflex Adaptor (Ovalflex on top to straight/round on bottom) with a small section of flexible liner and a Connector-Adaptor to connect to the insert flue.