▁is ▁available ▁in ▁various ▁bl ends . ▁A ST M ▁ 3 9 6 ▁recogn izes ▁bl ends ▁of ▁up ▁to ▁ 5 ▁percent ▁b iod ies el ▁as ▁equivalent ▁to ▁pure ▁pet role um ▁he ating ▁oil . ▁Bl ends ▁of ▁higher ▁levels ▁of ▁up ▁to ▁ 2 0 % ▁bio f uel ▁are ▁used ▁by ▁many ▁consum ers . ▁Research ▁is ▁under way ▁to ▁determine ▁whether ▁such ▁bl ends ▁affect ▁performance . ▁ ▁Old er ▁furn aces ▁may ▁contain ▁rub ber ▁parts ▁that ▁would ▁be ▁affected ▁by ▁b iod ies el ' s ▁sol vent ▁properties , ▁but ▁can ▁otherwise ▁burn ▁b iod ies el ▁without ▁any ▁conversion ▁required . ▁Care ▁must ▁be ▁taken , ▁however , ▁given ▁that ▁var n ishes ▁left ▁behind ▁by ▁pet rod ies el ▁will ▁be ▁released ▁and ▁can ▁c log ▁pip es - ▁fuel ▁filtering ▁and ▁prompt ▁filter ▁replacement ▁is ▁required . ▁Another ▁approach ▁is ▁to ▁start ▁using ▁b iod ies el ▁as ▁a ▁bl end , ▁and ▁decre asing ▁the ▁pet role um ▁proportion ▁over ▁time ▁can ▁allow ▁the ▁var n ishes ▁to ▁come ▁off ▁more ▁gradually ▁and ▁be ▁less ▁likely ▁to ▁c log . ▁Thanks ▁to ▁its ▁strong ▁sol vent ▁properties , ▁however , ▁the ▁furn ace ▁is ▁clean ed ▁out ▁and ▁generally ▁becomes ▁more ▁efficient . ▁A ▁technical ▁research ▁paper ▁describes ▁labor atory ▁research ▁and ▁field ▁tri als ▁project ▁using ▁pure ▁b iod ies el ▁and ▁b iod ies el ▁bl ends ▁as ▁a ▁he ating ▁fuel ▁in ▁oil - f ired