This Propex fixed directional vent is used with either 60mm (for HS2000) or 76mm (for HS2800) reducers to connect to the outlet ducting during heater installation. You would use this vent in the case that you want more than one vent in your installation. Use of a reducer is required.

You can find reducers here:
60mm (for HS2000 ducting): https://www.vancafe.com/2986106-p/2986106.htm
76mm (for HS2800 ducting): https://www.vancafe.com/2986122-p/2986122.htm