Look at posts 14 and 25 on my build thread. Definitely do not use an outside exhaust vent unless you plan on isolating the fish room from the house. It will pull the air inside your house outside and cause outside air to come inside you home. I originally had mine setup that way and it caused my electric build to go up almost a $100 a month during the summer.

http://www.maast.org/showthread.php?...Post-223/page2