I forgot which book, but in one of the earlier Files, Harry talked about how when working with magic, you gotta take physics into account - we've seen this more recently when he tossed the Cornerhound in the air and sent it flying, versus when it could hold onto the ground.
The example he used in this early Files was fire - how he had to draw the heat from somewhere, usually the air
That leads me to the question - why not draw heat from beings? Or cold, for that matter? Since Harry has that handy Winter boost, theoretically he could sling ice at one thing while superheating another by drawing the cold from that second thing. Or vice verse with fire.
Maybe he just hasn't thought of it, but Harry is awful clever when it comes to magical theory
