What is this and can I exhaust out of it?

[Northern_Loki]

@Esrgood4u

The single wall chimney system that’s installed and you plan on using are fitted and fine tuned to each stove.

I think the OP is referring to the currently unconnected exhaust fitting as opposed to the one fitted to the furnace (the one right below the furnace). Would there be concerns with exploring that exhaust?