Ceiling grid. Downdraft ceilings hold a set of diffusion panels in a plenum grid, and consistency across the set matters more than any single panel. Mixing old and new media in the same ceiling creates uneven face velocity, which shows up as drift and texture problems in the finish. Replace the ceiling as a complete set. We do not publish the SPB-76FD panel count yet because the record is pending verification; one measured panel and a grid photo through the fitment check locks it in.

Pit media. The exhaust plane takes fiberglass or polyester arrestor media sized to the floor grate or pit openings. Loading here is driven by what you spray and how much of it: primer-heavy schedules and high-transfer-efficiency guns load slower, heavy clear and production enamel work loads faster. A manometer or differential pressure gauge across the exhaust bed is the honest signal; the calendar is the backstop.

Change discipline. The expensive failure mode is stretching exhaust media past its holding capacity. Once an arrestor bed blinds over, booth pressure climbs, overspray starts finding gaps and seams, and cleanup costs exceed a year of filter spend. Set the interval from gauge readings during the first few cycles, then put deliveries on that cadence.

OSHA 29 CFR 1910.94(c) requires spray finishing operations to maintain adequate ventilation through the work zone, and a loaded exhaust bed is the most common way a compliant booth quietly becomes a non-compliant one. NFPA 33 adds the fire-safety layer: dry overspray accumulation in exhaust plenums and ducts is treated as combustible loading, and regular filter replacement is the named control. Shops spraying target-HAP coatings on vehicles or mobile equipment also carry EPA 6H obligations, including operating the booth per manufacturer specification and keeping maintenance records. Dated filter invoices plus a change log cover the documentation side.