Cycle math. Treat the booth as three ledger lines. The ceiling set is the big periodic spend: changed as a complete set so the intake plane loads evenly, on a cadence driven by finish quality and visible loading. Pit exhaust media is the frequent spend: it takes the overspray load and cycles on manometer reading. The AMU prefilter is the cheap insurance line: it protects the heater and blower, and it is the worst place to save money because AMU repairs dwarf a year of prefilter bags.

Intake side. Four sections, 78 x 134, per the AFT catalog record. Diffusion media across that plane is what turns heated makeup air into even, clean downdraft over a long cabin. Mixed old and new sections create velocity bias toward the fresh media, so partial changes cost finish quality.

Exhaust side. The pit run under an 8 meter grating is long, loads heaviest under the work zone, and is the stage EPA capture-efficiency numbers depend on. Dimensions vary by installation, so this position is locked during your fitment check, along with the AMU prefilter style (some older Blowtherm units run headerless frames).

Scale raises the stakes but not the rules. EPA 6H requires spray booth filter technology achieving at least 98 percent capture efficiency for target HAP coatings, met at the exhaust stage and maintained through timely change-outs. OSHA 1910.94(c) requires the ventilation system to keep pulling design airflow; on a cabin this long, a half-blinded pit shows up as dead air pockets mid-booth before the fan sounds different. NFPA 33 covers the fuel you are storing in the pit as media loads with overspray. Delivery records from a standing kit schedule are the cheapest compliance documentation you can own.