Abstract: A hollow shell recirculation arch underlies and supports at least one maple sap vaporizing pan. The arch is formed of inner and outer sheet metal shells. The inner shell is upwardly open and is sized smaller than the outer shell so as to form a space therebetween defining a first head exchange chamber. A transverse bridge wall is interposed within the inner shell, intermediate of the inner shell front wall and a rear wall, and separating the inner shell into a fire box and a second heat exchange chamber. Fire brick lines the interior surfaces of the fire box. Preferably the transverse sidewalls of the inner shell are V-shaped to concentrate and reflect the heat upwardly through the open top of the inner shell against the vaporizing pan.