This plenum is made of black molded plastic and snaps onto the outlet 'grille' of the mojave heater. It has a nipple to attach one, 2.5" flex hose (like dryer vent hose - not included) to the side of the plenum.
The plenum also has two round vents that can be rotated and which have two vanes that can be positioned to direct the airflow almost any direction or even closed to force air into the defrost hose.
When the plenum is snapped onto the heater, the total depth (front to back) is approximately 13".