In {TAIL ~ one embodiment}, the pipe itself forms {HEAD ~ a part} of the heat exchanger while in another embodiment, the heat exchanger is closed so as to form a heating chamber 
In { TAIL ~ one embodiment } , the pipe itself forms { HEAD ~ a part } of the heat exchanger while in another embodiment , the heat exchanger is closed so as to form a heating chamber
OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH