Quote Originally Posted by cozwin View Post
im guessing its a big air duct, most likely so that a side case fan could aim the air straight at cpu or other way around.

But tbh seems a little silly.

Why should it be silly? Using cooler air from outside the case instead of using the already warmed air inside the case seems silly? I don't think so.
But the problem is that you'll need a case with an opening or a case fan exactly positioned above the CPU. I know for sure that there are some cases available that have it, so it doesn't seem too bad of an idea to me.
The only thing that I don't like about the heatsink is the stock 80x80x20mm fan. Seems a bit too weak for my liking.

And as PcCI2iminal already showed, you'll need a high speed fan with that heatsink as the fin density is kinda high. Low speed fans won't be able to push enough air through the fins to effectively cool the heatsink down.