https://bitcointalk.org/index.php?topic=155872.msg1651925#msg1651925if you want to replace the fan, please use ONE 12038(or 12044) size, 4PIN PWM, 12V , with at least 3600RPM maximum speed. ball bearing is recommend.
a 1200rpm 12025 fan (or 2 in series ) will of course kill the machine.
For future reference those number are decoded as:
"If you want to replace the fan, please use ONE 120mm x 38mm (or 120mm x 44mm) size, 4PIN PWM, 12V , with at least 3600RPM maximum speed. ball bearing is recommend.
a 1200rpm 120mm x 25mm fan (or 2 in series ) will of course kill the machine."
That's Avalon recommended. You can use less powerful fans as long as the room ambient temperature is low (say, the same as in a server room) and you are using the standard Avalon case or an Aluminum one where heatsinks are directly mounted to Aluminum base. If you're using a design where the heatsink is NOT directly mounted to an aluminum base you're very limited with your overclock ability. There's a good reason why the Avalon heatsinks are mounted to the aluminum base. The base increases heatsink surface area and, accordingly, acts like a heatsink drawing heat from actual heatsinks.
If you want to save money don't use a 4 pin PWN fan but use a 3 pin non PWN fan.
Also, see:
https://bitcointalk.org/index.php?topic=253382.0(Google search:
http://bit.ly/1c5kjUG)
