@ryanc But also, yeah, more I'd just say that the box fans I've tried to clamp down, even in windowframes, tend to get real wobbly real fast. I'm also using what are probably the cheapest box fans available, you can probably do better, but they work fine as box fans - I just would probably regret trying to make them a ceiling fan.
That said, I also don't love air blowing on me, so I get most of the de-stratification benefit by pointing a fan up into free space from the floor.