wherein the furnace has a series of airbox zones beneath {HEAD ~ the bed} extending serially from {TAIL ~ 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 the input end 
extending serially from
wherein the furnace has a series of airbox zones beneath { HEAD ~ the bed } extending serially from { TAIL ~ 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 the input end
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL 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