/diy/ - Do It Yourself

My dad passed away last year and I just moved into his house. It has a wood stove that he used as his primary source of heat. I know the basics of wood stoves, but as far as how to run it to get the most efficient burn, I'm a little lost. The only controls on it are the primary air intake on above the front door, and another knob you can turn on the side. The knob on the side opens a long, narrow door that runs along the ceiling of the front of the stove. I'm not sure what this does exactly so I'm hoping someone here can help.

The knob can be set to either keep that door completely open or completely closed, with no in between. When I have it open, the stove seems to be pulling in a lot of air and will give me a good sized flame, which burns the wood quicker than I think it should, which I don't think I want for efficiency. When I close it, it kills the flame and I end up with embers just smoldering, but they last for hours. The problem is that sometimes when I close that vent, I get intermittent "coughs" of smoke every ~5 seconds out of the intakes and some around the door. Sometimes it'll run fine for hours with no coughs of smoke, and sometimes it'll give me nonstop coughs until I open that long door up again. It also loads the inside of the stove with smoke no matter what and turns the glass on the door pitch black to where I can't even see inside.

Does anyone know what exactly that door does, or even the name of it so I can do some Googling? And when I get it running well with the door closed, do I want it to run like that so the wood is smoldering but putting off a bunch of smoke in the stove and out the chimney but not into the room? Is that my most efficient burn?

Picrel is that door along the top of the stove's ceiling I'm questioning.