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