Lane Lewis wrote:

Generally one more fan blowing in than out, taking into consideration
the
PSU fan.

This creates a positive pressure in the case.

This depends totally on your environment. In a dusty environment, yours
is a good solution - no air and dust entering case through drive openings.

In a low dust or no dust environment, you *want* cool air flowing over
your drive devices, so exhaust fans should out number input fans, that
is, more fans blowing out than blowing in.

Why does more exhaust fans mean more air ?

Who said it does?

All I said is that having more exhaust fans than input fans (or more
accurately more exhaust fan CFM than input fan CFM) will cause cool
air to flow into the case across drive devices.

Read it again, Lane.