The 50BV single-piece units come with 1-in. filters. The standard 1-in. filters provide lower pressure drop and longer filter service intervals. The 50BV modular units come with 4-in. filters.
Inspect air filters every 30 days and replace filters as necessary.
Replacement filters should have a minimum efficiency rating of MERV 6 per ASHRAE rating procedures and be rated for up to 625 fpm velocity. Job requirements or local codes may specify higher minimum ratings.
Source: MaintainX (Community Member)