I wonder if HT could burn Ace the same way Akainu do, after all he is hotter. But then again, maybe thats not enough, maybe you need haki.
And, Ace is far stronger and faster in a fight, and he has Haōshoku Haki, so he could just KO him.
" @Mortein: Human Torch is just as fast if not faster. He's marginally above supersonic. But I agree on Haki. "Well, pre time skip luffy was faster then sound, and I think Ace was faster then luffy. No doubt HT can travel faster then Ace, but in a fight Ace should be faster.