We recently moved into a larger home. Our old home had one spot for filters and was pretty straight-forward. The new house has a main area in the upstairs hallway for a large 20x36 filter and I believe this is also where air from the outside comes in (SmartVent system). In the master bedroom walk-in closet ceiling there is another area for two smaller filters that does not pull in any air from the inside of the house (just a spot to replace filters). In the attic (which is accessed from the same closet) there is a switch that appears to turn on some kind of fan, or something that sounds like one. Based on the location, it would appear that these other filters are related to this fan.

My only guess was that this switch controlled an attic fan, but I thought those were intended to turn on/off automatically based on temp (the attic was very cool already). I also didn't think attic fans used any kind of filtering. Looking for any guidance on this....Thanks!