The ovens I've seen similar to this before are more like "grey" ovens, lol. Like a white oven they have a fire box bellow the oven chamber but unlike a white oven the flame, heat, and smoke directly enter the oven chamber through an opening in the floor. They are similar to a guillard oven, but in a guillard oven the floor is insulated like a black oven, in these ovens the floor is uninsulated and therefore directly heated by the firebox which it serves as the ceiling of.