I can put a filter on my intakes. Whether it is positive pressure depends on the fan speed I choose in relation to the exhaust fans.
The filter restricts airflow too much in hot weather. I'd need more surface area/ pleats and have the filter further from fan blades to help that.
There are imprints of dirt where the axial fans reside, and washing the filter reveals the surprising amount of **** caught, but cigar ash dust?.... Likely not effective on that, not until the filter is so loaded the fan can't move much air.
One interior fan i can put a filter on too. I use a few layers of filter media with an exterior of carbonactivated filter , and it does not take long at all for that one to show visible signs of collecting clothes lint and dust. I vaccuum it every week or two
