Intake side. The Thesis feeds air down through a ceiling plenum lined with diffusion media, the position that decides whether a large panel lays down clean or collects debris. In a booth sized for bigger vehicles the ceiling bank is long, so panel count matters as much as panel size when pricing a changeout. Count the grid openings, measure one panel and its frame opening, and the intake fitment is settled; we hold it on file.

Exhaust side. Overspray leaves through arrestor media below the floor grating. Fiberglass pad and roll stock dominate this position on legacy European downdrafts because they cut to the pit layout without OEM framing, and roll goods are usually the economical answer for a longer booth. This is also the position to inspect first when buying a used Thesis: pits hide neglect, and a booth that sat idle often has media in it that should have left years ago.

Cycle math. Exhaust drives the schedule; it takes the whole overspray load while ceiling media only cleans incoming air. Change exhaust on pressure rise if the booth has a working gauge, or on visible loading and pressure drift if it does not. Ceiling media runs a longer interval but has a hard stop: the first fiber it sheds into a wet clearcoat cost more than the panel set.

An orphaned booth has no compliance exemption. EPA NESHAP 6H requires shops spraying target-HAP coatings to do it inside a filtered enclosure with maintained, documented filters; inspectors do not care whether the manufacturer still trades in the US, only whether the media is intact and the changes recorded. OSHA 29 CFR 1910.94(c) holds the booth to real ventilation performance, which degrades as fast as the exhaust media blinds. NFPA 33 treats caught overspray as combustible loading, so a Thesis pit full of aged arrestor is a fire finding waiting to be written. A standing filter schedule with dated deliveries answers all three.