Reason for 2 1 filter slots on hvac Merv 2 and 5

Reason for 2 1 filter slots on hvac Merv 2 and 5 return air support box with filter slot I've also sorted a housing for the stale air return that holds a 16x25x1 filter so I can pull the restrictive exchanger filters on both supply return to the feature slot This is just one of many ways to form a return air box or plenum for an electric air handler to

return to the feature slot 38 x 28 x 15-38, Hot Dip Galvanized Steel, Return Air, Sheet Metal Duct Support Box 5908000 16 X 25 1 FILTER HOLDER · 5908000 16

return of the dead slot Return Air Support Box w Filter Rack Description: Support Box w Filter Rack; Size: 40 x 28 x 15; Gauge: 26; Duct Size: 10 x 25; Order #: M90-482  Protect your mailing with packaging products From cushioned envelopes to sturdy cardboard boxes and high quality packing tape