Ideally you want an enclosure with a BOTTOM fan that blows IN. There's only a few out there like that. I made my own: fan on bottom and it's an enclosure that can also house optical drives, so it has a removable front and there I put one of those 3 x 40mm fan bay coolers, and I put a grill in the top for exhaust. People and manufacturers seem to forget the hottest part of a HD is its underside. Most enclosures only have a tiny weak rear fan that's really only for cooling their internal power supply! Many enclosures that use an external PS don't even have fans! So watch for those things. Also don't forget their PS's may not be powerful enough for extra fans. My bottom fan is an AC fan that I have wired directly to the AC coming into the unit.