Side Downdraft vs Full Downdraft Paint Booths

Wall Exhaust Columns Compared With Floor Grates

In a side downdraft booth, exhaust plenums run along both long walls with filtered intakes near floor level. Air drops from the ceiling, sweeps down past the part and then turns outward toward the walls. In a full downdraft, exhaust openings sit in the floor beneath or alongside the part, so air leaves straight down. The visible difference is the wall plenums, which take up some interior width, and the absence of grates or a trench in the floor.

• Side downdraft: exhaust ducts and filters are built into the side walls, often with ducting running up to a shared fan.
• Full downdraft: exhaust runs below the floor to a fan, often at the rear or side of the booth.
• Both use a ceiling intake plenum fed by a make-up air unit.
• The floor in a side downdraft stays flat and solid, which helps with carts, lifts and cleaning.

Avoiding the Pit: What You Save and What You Trade

The main reason to choose a side downdraft is to skip excavation. No saw cutting, no trench forming, no concrete pour and no drainage design inside the pit. That matters in leased buildings, plants with post-tensioned slabs, floors with buried utilities, and sites where the schedule cannot absorb concrete work. Avoiding a raised basement also means no ramps and no step at the door, which helps with vehicles, forklifts and rolling carts. The trade is interior width. The wall plenums consume space on each side, so a side downdraft cabin needs a wider exterior footprint to deliver the same working width as a pit booth. In tight bays, that extra width can be the factor that rules it out.

Performance on Wide, Tall and Low Parts

Airflow in a side downdraft has to travel from the center of the booth out to the walls. On narrow and medium parts this works well, and the finish can be comparable to a full downdraft. On wide parts, air reaching the center underside of the work has farther to go before it reaches an exhaust opening, and areas low and in the middle can see slower air movement. Full downdraft booths pull directly beneath the part, so air speed is more uniform across the width. For tall parts the two behave similarly near the top, but the full downdraft keeps a cleaner vertical pattern near the floor.

• Measure the widest and tallest parts you expect, not the average.
• Consider how parts are positioned: centered vehicles, staged fixtures or parts on carts.
• Low surfaces such as rocker panels or lower enclosure edges benefit most from floor exhaust.

Install Work and Utility Connections

With no pit, a side downdraft install can move from layout to booth assembly quickly. The heavier work shifts to the walls and roof: the exhaust plenums are assembled into the side panels, ducts run up to one or more exhaust fans, and the stack or stacks pass through the roof. That may mean more roof penetrations or longer duct runs than a pit booth with a single rear exhaust. The make-up air unit, gas piping, electrical service, lighting, controls and fire suppression connections are broadly similar for both designs. Sprinkler or suppression nozzles must cover the wall plenums as well as the cabin, and the authority having jurisdiction will review the exhaust layout along with the rest of the booth.

Living With Each Design Day to Day

Maintenance in a side downdraft is concentrated at the wall filters, which are reachable without lifting grates or climbing into a pit. Floor cleaning is simpler because there are no grates to collect overspray and debris. Full downdraft booths require periodic grate cleaning, pit filter changes and trench housekeeping, but the floor exhaust spreads the load across a larger filter area. In both designs, intake filters, exhaust filters, burner checks and pressure balance should follow a set schedule, and filter loading should be watched closely because a clogged wall or floor filter changes airflow patterns quickly.