In many cases, {HEAD ~ existing ovens} can be used as {TAIL ~ the heating source}, without modification 
used as
In many cases , { HEAD ~ existing ovens } can be used as { TAIL ~ the heating source } , without modification
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH