Brazing rods

[Mtsaz]

Hi...for copper hvac brazing i have always used sil fos 15.  Today while installing a txv i was short just a few inches worth and had some Harris 15 rods someone gave me.  I had to adjust the flame and they took more heat to flow the same.....or so it seemed.   Had anyone noticed any difference among silfos15 and other brand copies?  I would expect them to be very close if not identical but my experience today makes me wonder.  What do you use?  Thanks