Join Date: Feb 2012
Location: Ontario, Canada
The angle of the fan plus the fan output determine how much lower than room temperature it gets. Aim the fan directly to the water surface gives you the best result. When my room temp is 80+, I have no problem getting the tank to 70 with a 50 CFM computer fan on a 20G tank.
Another thing to note is, you can hook up the fan to a timer and do like X min on, X min off and adjust the X according to the room temperature so you tank has a relatively stable temperature.