wherein the furnace has a series of {HEAD ~ airbox zones} beneath the bed extending serially from adjacent the input end to adjacent the output end thereof, including a minority of said airbox zones adjacent the input end of the furnace and a majority of said airbox zones remote from {TAIL ~ the input end} 
wherein the furnace has a series of { HEAD ~ airbox zones } beneath the bed extending serially from adjacent the input end to adjacent the output end thereof , including a minority of said airbox zones adjacent the input end of the furnace and a majority of said airbox zones remote from { TAIL ~ the input end }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL