There's not much room for an exhaust fan. The PSU /motherboard are packed tight, and since it's a slimline, there's very little space between one edge of the mobo and the side of the case. I mean...I'm sure I could make it work somehow, but yea.
It's a pretty tight fit as it is, thus why I was leaning towards a vent. I could probably fit a fan closer to the HDD or smaller unoccupied spaces between the case/mobo, but I dunno. Air flow and I aren't friends.