There is disclosed a furnace having {HEAD ~ an air flow path} for heated air and combustion products that passes through {TAIL ~ a condensing heat exchanger} 
passes through
There is disclosed a furnace having { HEAD ~ an air flow path } for heated air and combustion products that passes through { TAIL ~ a condensing heat exchanger }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL