Piece of advice... Don't scrimp on the fans, I learned this the hard way. Cheap extraction fans aren't designed to run 24/7 with hot airflow and they will burn out quickly, even when over-specced.
If your budget will allow, go for 3-phase fans, specced well above the airflow requirement and with a transformer-based controller.
I'm currently looking at 2x 36" 1/2HP fans from Hessaire. Has decent reviews and at 350/unit its not terrible either.
They're spec'd to 11000CFM each, so should be good?
are they both for out flow?
100 s9 units are about 100 x 220 = 22000 cfm on the little unit fans.
So 11000 cfm in and 11000 cfm out is not enough.
22000 cfm out works.
passive intake is okay if big enough and filtered.
we use metal reusable filters like these:
https://www.mcmaster.com/air-filters/heavy-duty-reusable-metal-panel-filters-11/or these
https://www.mcmaster.com/air-filters/made-to-order-heavy-duty-reusable-metal-panel-filters/these save a fortune in replacement costs.
you still may need to clean your s9's every 3 to 6 months.
We have a very dirty environment out side of the mining room. So we clean the metal filters monthly and we clean the gear every 100 days.