{TAIL ~ The heat exchanger burner} can be fueled by {HEAD ~ natural gas}, methane, propane and the like 
{ TAIL ~ The heat exchanger burner } can be fueled by { HEAD ~ natural gas } , methane , propane and the like
TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH