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