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