Side downdraft paint booth: a down draft finish without cutting your slab

October 26, 2026 · Marathon Finishing Systems

A side downdraft paint booth pulls filtered air straight down through a full ceiling and out low plenums along both side walls. You get a true down draft finish on a flat slab, with no pit and no concrete work. Overspray falls away from the panel instead of riding along the part.

Shops that ask for a down draft booth usually want two things: clean air coming straight down over the work, and overspray that leaves the booth without riding along the part. A Full Down Draft does that through a pit in the floor. If you lease the building or the floor is already finished, Side Down Draft is the booth we lead with at Marathon Finishing Systems, a spray booth manufacturer in Temecula, California.

Here is how it works, how it compares, and when the pit is still the better call. For the full picture, start with the six airflow patterns we build.

What is a true down draft paint booth?

A true down draft paint booth brings filtered air in through the whole ceiling, moves it straight down and exits it low. Every paint booth comes down to where the air comes in and where it goes out. In a cross flow booth, air enters at one end and travels the length of the booth, so overspray from the front of the part drifts across the back of it. In a true down draft, overspray falls away from the panel toward the floor, and the air carries far less dust and overspray across the work.

Two Marathon patterns are true down drafts, Full and Side. Both take intake through a full ceiling of diffusion media. The difference is where the exhaust goes.

Do you need a pit for a down draft booth?

Only for a Full Down Draft, and the pit is costly and slow. A Full Down Draft exhausts through grating in the floor into a filtered pit below the slab, then on to the exhaust fan. The pit is the exhaust path, with grating and filters over it, and it has to be built to the booth's pit drawing. A contractor saw cuts the slab, excavates, pours to the drawing, and waits for the concrete to cure before the booth can be set. Drainage, slab flatness and the concrete itself are owner scope.

In a leased building that usually means a landlord's sign-off and a look at what is under the slab. In a finished building it means cutting a floor you already paid for. Full Down Draft is the only pattern we build that needs concrete work.

How does a side downdraft paint booth move the air?

A Side Down Draft keeps the full ceiling intake and, instead of a pit, exhausts through a pair of low filtered plenums that run along the base of both side walls for the working length of the booth. Filtered air comes straight down over the whole floor area, same as a Full Down Draft, sweeps to the nearest wall and leaves through those low filters, all on a flat, level slab. No saw cutting, no pour, and no waiting on concrete to cure.

Because the exhaust runs the full length of both walls, the pattern holds anywhere in the booth. On a long unit with two or three painters working at once, or a floor with several parts spread out, each painter is standing in their own down draft instead of in someone else's overspray. It is the reason Side Down Draft is our default for large industrial and truck work.

Heat is an option, quoted with the pressurized intake plenum, with prep, spray and cure modes. Heat is not available on Front Flow or Open Face, so a bake cycle already narrows you to Semi Downdraft (we call it Modified Down Draft), Side Down Draft, Full Down Draft and Reverse Flow.

Look at the photo of the inside of one. White filter pads across the whole ceiling, a row of low filters along the base of each wall, and a flat, open floor.

How much wider is a side downdraft booth?

A side downdraft booth needs about 4' to 5' more outside width than the inside dimension, because the side plenums live outside the working width. A 16' inside booth comes in at a little over 21' outside. If you are fitting a booth between columns, measure to the outside of the plenums, not the inside of the booth. Longer booths, around 50' to 60', use four plenums instead of two, with more and smaller exhaust fans. We quote the model, not the fan count.

Send us your largest part and our sales team will review the layout with you.

Side Down Draft vs Full Down Draft vs Semi Downdraft

A short answer first. Full Down Draft is the best finish we build. Side Down Draft gives you down draft finish quality with no concrete. Semi Downdraft is a good booth, but it is not a true down draft.

Semi Downdraft takes intake through the front section of the ceiling only, with the product door right under it. Air enters above the door, then travels the length of the booth to a filter bank on the rear wall. The air travels from the front ceiling intake to the rear, so the longer the booth, the better the pattern works. It is essentially a crossdraft with the intake in the ceiling. It fits a narrower bay, because there are no side plenums, and it takes heat. If your building cannot give up the width, it is a real option. If you are choosing it for the finish, choose the length too.

When Full Down Draft is still the better call

If you are chasing the best possible finish, you own the building, and a pit is on the table, pour the pit. Vertical flow over a grated floor holds everywhere in the booth, and overspray never crosses the work or the door opening. Drafting gets the pit drawing to you early so your concrete contractor can price and schedule it before the booth ships.

There is a middle path. On select Full Down Draft models, or engineered for others, the booth can sit on a Raised Basement, which puts the pit about 12" above the slab with ramps at the main doors and a step at the man doors. You get the floor exhaust without cutting concrete, at the cost of a step up and a foot of height.

Questions to ask before choosing

Settle these before anyone draws a booth for you.

1. Do you own the slab, or does a landlord? Who signs off on cutting it, and what is under it?
2. How many painters work at once, and how big is the largest part side to side?
3. What is the bay width between columns, measured to where the side plenums would sit?
4. Does the coating need a bake or force dry? That rules out Front Flow and Open Face before anything else.
5. What finish do your customers actually inspect, and would a Semi Downdraft at the right length get there?

If the answers come back leased building, more than one painter, and a finish that has to be better than cross flow, the answer points to Side Down Draft.

Send our sales team the part and the building, and we will tell you which one fits and why. You can see built examples on our truck and large equipment booths page. Or hop on a call and we will walk through it. Which side of the slab question are you on?