Simply described, the stacked air system works by stacking ports on top of each other. Fewer ports are typically used at a specific elevation, but there are more elevations throughout the height of the furnace. Anthony-Ross typically uses two or three ports on two walls at both the secondary and tertiary air levels in an interlaced pattern when the folds are made (as shown below). The ports are on the same tube locations vertically. Depending upon the CFD Model results, one or more elevations may be added.