How does old wood furnace work?
I think that might be an old coal burner with a dome heat exchanger on top (also known as a radiator).

I have never seen or used one of these in person, but there is some information about this stove type sparsely spread around the internet.  I understand they are roughly 1940s vintage.

Consider this photo of a competing Wards model:



Ash tray is the bottom door.  Coal is added through the middle door and air inlet is controlled at the middle door and/or bottom door.   The top end is a heat exchanger that circulates flue gas to the center dome, then to the front part of the doughnut, around the sides, to the back, past a manual balancing damper at the flue connection and then up the chimney.  The manual balancing damper at the flue would be needed to manage airflow in concert with the intake.  I believe the front door on the dome is there for cleaning and remains closed during normal operation.

This stove is not likely to be efficient by today's standards because it is not equipped with a secondary burn chamber.