I have always wondered what this contraption on the back of my Hearthstone soap stone fireplace is. There is a horizontal tube with little holes in it that runs along the back of the inside, about halfway up — kinda looks like a burner. On the right exterior side, there is a movable cover over the “burner” pipe, though it sits about 1/4 inch open gap off the soapstone so it certainly doesn’t seal anything. Then there’s some craziness on the back that defies explanation ... a lever to some kind of flapper that lines up with a rectangular box inside, at one end of the “burner” tube. Any ideas??