I am absolutely certain that all claims that the Knights Templar were heretics as absolute rubbish. It was a convenient claim by the King of France, that allowed for him to seize much of the vast wealth of the Knights Templar when his own coffers were relatively empty. If I recall correctly he also owed quite a large sum to the Knights Templar who functioned similarly to a medieval bank (but with no interest). I believe that the absence of heresy is perhaps best supported by the dearth of confessions of heresy on the part of the tortured Knights Templar. As we all know, people will tell you anything you want if you put them in enough pain, but this wasn't the case for many of the Knights Templar.

But yes, all I've read on the subject has rubbished the idea of Templar heresy. I should stress that I haven't read a huge amount though, so there may be evidence I don't know.