if the filter is the same distance from the fan, there really isn't much of a difference. Filter after the fan is perhaps a bit better from a turbulence and noi

if the filter is the same distance from the fan, there really isn't much of a difference. Filter after the fan is perhaps a bit better from a turbulence and noise perspective. https://www.quora.com/Where-should-an-air-filter-be-placed-relative-to-the-fan-for-best-efficiency https://www.quora.com/Where-should-an-air-filter-be-placed-r... One thing to keep in mind though is most filters have an expected direction of airflow, which does matter both to its efficacy and efficiency.