You bought filters that fit your old shop's booth, dropped them into the new one, and nothing lines up — or worse, your finish quality fell off a cliff after the swap. Nine times out of ten the culprit isn't the media, it's the airflow layout. A downdraft booth, a crossflow booth, and a semi-downdraft booth move air in completely different directions, which means they place intake and exhaust filters in different spots, size them differently, and run them at different face velocities. Get the layout wrong and you're fighting dirt, pressure problems, and wasted money on filters that don't do their job.
This guide breaks down the three common booth types, shows where the intake and exhaust filters live in each, and explains how the layout changes the filter size, placement, and airflow math you need to order correctly.
The three airflow layouts at a glance
Every downdraft, crossflow, or semi-downdraft booth is really just a plan for moving clean air from the intake side, across or over the part being sprayed, and out through the exhaust side. The difference is the path that air takes.
| Booth type | Air path | Intake filters | Exhaust filters |
|---|---|---|---|
| Crossflow | Horizontal, front to back | Doors / front plenum | Rear wall |
| Downdraft | Vertical, ceiling to floor | Full ceiling | Floor pit / grates |
| Semi-downdraft | Diagonal, front-ceiling to rear-floor | Front section of ceiling | Lower rear wall |
If you're still getting your bearings on which end pushes and which end pulls, our primer on the direction of airflow in paint booths is worth a read before you order anything.
Crossflow booths: the horizontal workhorse
Crossflow is the oldest and most affordable layout, and it's still everywhere in general-repair and production shops. Clean air enters through intake filters mounted in the front doors or a front plenum, travels horizontally the length of the booth, sweeps across the vehicle or part, and exits through exhaust filters on the rear wall.
Because the air moves parallel to the floor, overspray travels with the airflow toward the back — which is exactly why the back of a crossflow booth tends to collect more haze and why the operator should generally work front-to-back, keeping the freshly sprayed surface downstream of themselves.
What crossflow means for your filters
- Intake: a relatively small bank of panel or pad-style intake media in the doors. Because the intake area is concentrated, face velocity through those panels is comparatively high, so they load faster and want checking often.
- Exhaust: a full rear wall of exhaust media — typically fiberglass, polyester, or accordion-style paint arrestors sized to the wall opening.
- Design velocity: NFPA 33 is the governing standard for booth airflow and fire safety, and crossflow booths are commonly engineered around roughly 100 feet per minute (ft/min) of cross-sectional air velocity — that is, the average speed of air moving through the empty booth cross-section. Confirm your own booth's rated velocity on its data plate; don't assume.
Downdraft booths: the finish-quality standard
Downdraft is what the high-end collision and custom shops chase because it delivers the cleanest finish. Air enters through intake filters that cover the entire ceiling, floods straight down over the part, and exits through exhaust filters in a floor pit or under floor grates. Overspray is carried down and away from the surface being sprayed rather than dragged across it, so dirt has far less chance to settle back onto wet paint.
That performance comes at a cost: downdraft booths need a pit, a basement, or a raised floor to house the exhaust plenum, and they need a lot of ceiling filter area.
What downdraft means for your filters
- Intake: the big one. A downdraft booth's whole roof is a filter bank, so you're buying ceiling intake filters by the panel or the roll — usually tackified diffusion media (often rated F5/M5 to EN 779 / ISO 16890) that both cleans the air and distributes it evenly across the ceiling. Even distribution is the whole point; a loaded or mismatched section creates a dead spot right over the part.
- Exhaust: floor-level arrestors sized to the pit or grate openings. Because the total ceiling intake area is huge, the face velocity per square foot of intake is low, which is part of why downdraft air feels so gentle and even.
- Design velocity: downdraft velocity is measured as the downward air speed in the working zone over the part. The larger filter area is what makes a slow, laminar, top-to-bottom sweep possible.
Semi-downdraft: the practical compromise
Semi-downdraft splits the difference for shops that want better-than-crossflow quality without excavating a floor pit. Air enters through intake filters in the front portion of the ceiling, angles down and back over the part, and exits through exhaust filters low on the rear wall. The result is a diagonal sweep — not as clean as full downdraft, but noticeably better than horizontal crossflow, and it installs on a slab.
What semi-downdraft means for your filters
- Intake: ceiling media over the front third-to-half of the booth. You're buying less ceiling filter than a full downdraft, but it's the same style of tackified diffusion media.
- Exhaust: a rear-wall bank, lower-mounted, sized to the exhaust opening.
- Practical note: because intake is concentrated at the front, the front-to-back finish gradient is real — work with it, not against it.
The airflow math that ties it together
Two numbers govern every layout: total airflow (CFM) and face velocity through the filters. Face velocity is simply the airflow divided by the filter face area:
Face velocity (ft/min) = Airflow (CFM) ÷ Filter face area (sq ft)
This is why booth type dictates filter size. A downdraft booth pushes the same rough order of airflow through a much larger ceiling area, so its face velocity per panel is low and its air is gentle. A crossflow booth pushes air through a small door-intake and a single rear wall, so face velocity is higher and filters load faster. When you change a filter, you're really managing face velocity — keep it in the media's rated range and both airflow and capture efficiency stay where they belong. If your numbers drift, our guide to troubleshooting low airflow in a spray booth walks through the fixes.
Don't confuse intake filters with exhaust filters
Every layout has both, and they are not interchangeable. Intake (ceiling/door) media is built to clean and diffuse incoming air; exhaust media is built to capture paint overspray. For NESHAP 6H compliance, the exhaust stage is the one that matters — 40 CFR 63.11173(e)(2)(i) requires exhaust filter technology demonstrated to capture at least 98% of paint overspray by weight (tested per ANSI/ASHRAE 52.2 or EPA Method 319). Note that's a weight-based capture figure, not a "98% at 3 microns" particle-size spec — that phrasing is vendor shorthand and doesn't match the rule. If you're unclear which side is which, our breakdown of the difference between intake and exhaust filters sorts it out — and getting the two banks to load in sync is its own discipline, covered in balancing your booth's intake and exhaust filters. This isn't legal advice — confirm requirements with your state or local air authority.
Matching filters to your booth: a quick decision path
- Identify the air path. Front-to-back = crossflow. Ceiling-to-floor = downdraft. Front-ceiling-to-rear-floor = semi-downdraft.
- Locate both filter banks. Find the intake bank (doors or ceiling) and the exhaust bank (rear wall or floor pit).
- Measure the openings. Get the width, height, and depth of each bank so you order the right size; our guide on how to measure for the right filter size shows exactly what to record — and this is where a custom cut often beats a forced fit.
- Match the media to the stage. Tackified diffusion media for ceiling/door intake; 98%-by-weight arrestors for exhaust.
- Check face velocity. Confirm the filter's rated velocity range covers your booth's CFM-per-area.
For a deeper walkthrough of choosing media by stage and booth type, see how to choose the right paint booth filter by stage, media, and booth type.
Frequently asked questions
How do I tell if my booth is crossflow, downdraft, or semi-downdraft?
Look at where the filters are. Filters in the doors with an exhaust wall at the far end is crossflow. A full ceiling of filters with a floor pit is downdraft. Ceiling filters only over the front, with exhaust low on the back wall, is semi-downdraft.
Can I use the same exhaust filters in any booth type?
Often yes for the media type, but not the size. Exhaust arrestors are sized to the specific opening — a rear-wall bank and a floor-pit bank need different dimensions even if the media is identical. Always measure your opening.
Why does a downdraft booth use so many more intake filters?
Its entire ceiling is the intake bank, so it needs far more square footage of media than a crossflow's door intake. That large area is what keeps face velocity low and airflow gentle and even over the part.
Does booth type change my NESHAP 6H compliance obligation?
No. Regardless of layout, your exhaust stage must use technology demonstrated to capture at least 98% of overspray by weight. Booth type changes filter size and placement, not the capture requirement. Confirm specifics with your local air authority.
Order the right filters for your layout
Once you know your booth's airflow path and have your opening dimensions, browse our ceiling intake filters for downdraft and semi-downdraft roofs, and our paint booth exhaust filters for the capture stage. Not sure what fits? Use our Find My Filter tool or reach out — send us your booth make, model, and opening dimensions and we'll match you to the correct media and size, custom-cut if needed.