Lol, I did this in the dorms in college, by the end of the first term I had a thick ass ring of resin built up on my screen where the fan was, it was nasty!
Except I didn't use a window fan, I used a regular fan that I just stuck in the window. It pulled a lot better than a box fan and I didn't have a window fan, though I've used them for the same purpose and they work really well. Through my own stoner-research I've concluded that the box fans are the most popular for this though, I remember standing outside a big dorm on campus and looking at all the windows, like every third window had a box fan turned backwards with cardboard blocking the other half of the window, so smoke wouldn't come back in.