Sorry, but in my experience, none of the fans I have wired up directly to an extension cord and plugged into the wall have overheated. They run for months(4+) continuously and do not overheat.

http://www.radioshack.com/product/in...ductId=2102823

This is the one I got. Works fine. The 3" got too hot for the incubator, however the 4" works perfectly.