This is a hot air register. The ductwork brings to hot air to each room. The ductwork is located in the basement ceiling and up through the walls with open ports called registers.
There is a flapper on the register that makes it open or closed.
The duct behind the wall has a register on the other side that let's hot air into the next room. The ductwork continues upward to the second floor and has a third register for an upstairs room.
There is another duct that goes to the other room upstairs. The second room upstairs had no heat and eventually we determined that a duct hose was hooked up incorrectly. The problem is solved now.
In the wood burning room, we have wood stacked up, dried and ready to use.
So, using gloves, we open the door, open the draft and lift and place wood into the wood box. The fire is going, so there is a small amount of smoke that puffs out the door.
When done putting wood in the doors are then closed and latched.