Exhaust side first. On a cross-flow, the exhaust wall grid is where the money goes. It takes the entire overspray load, so it cycles fastest and matters most for compliance. Kleen-family enclosures carry vertical grids that accept standard arrestor formats: fiberglass pad, polyester pad, or pleated paper, depending on the grid framing. Count the openings, measure one, note which media style is in there now; that is the whole exhaust fitment.

Intake side. Supply air enters through filtered doors or an intake wall. Intake media on a cross-flow protects finish quality by cleaning incoming air, and it usually runs a longer cycle than exhaust because it never sees overspray. If your Kleen Box pulls make-up air through a heater or air-handling unit, there may be a pre-filter stage upstream of that unit too, and it should be on the same reorder list even though it hides out of sight.

Cycle math. Plan around the exhaust grid. When exhaust pads load, cabin pressure goes positive, overspray starts drifting out the door seams, and capture efficiency falls; that is your change signal if no gauge is fitted. Replace intake media on a slower multiple of the exhaust interval and whenever it shows visible dirt bleed-through.

A Kleen Box used for coating work sits under the standard three-layer rulebook. EPA NESHAP 6H requires target-HAP spraying to happen inside a filtered enclosure with documented filter maintenance; an undocumented legacy booth becomes documentable the day you put it on a recorded change schedule. OSHA 29 CFR 1910.94(c) governs ventilation performance, and a loaded exhaust grid is the usual reason a booth that passed its last inspection fails the next. NFPA 33 concerns the overspray already caught: dried arrestor loading is combustible, which is why changes belong on a schedule and used media belongs in a closed metal container.