I think we should move on and just help the OP with his problem
I think to make thing clear, we all need to know what excactly is his system.
Conditioned Air Flow
this comes from outside, inside or a mix,
it passes through a filter, heatexchanger, fan widget or what ever.
just a true description of what the process is. (as it would seem that we all have different ideas of what we are talking about, thus are giving different solutions based upon what we think we are dealing with) I think once this done we should all be singing on the same song sheet!