Spray Booth Fan Recommendations

[Andrew McSpadden]

I am going to build a small portable spray "closet" that I can roll up to a window for exhaust. I need to do this because I usually spray outside but am getting enough repair and new work that I need to spray year-round.

I mostly spray water based (HVLP and LVLP) but occasionally I have to repair lacquer or spray flammable stuff.

Any small explosion proof fan recommendations? Warnings? Advise? Thanks!

[David King]

Andrew, the trick is getting "make up air" back into the booth and keeping that air dust free, warm and dry. You're going to be limited by fire code as to what qualifies as an explosion proof fan and basically all of them are belt driven with the belts and pulley inside a sealed shroud so that the motor, wiring and switch are all outside the VOC area. By code your booth enclosure should be rated for a 2 hour burn-through which means a certain gauge of steel or 2 layers of 5/8" thick sheet rock. All booths are supposed to have an automatic fire suppression system usually an ABC fire extinguisher connected to overhead jets but water sprinklers will also probably pass muster. Any and all wiring inside the booth needs to pass through sealed, threaded (schedule 80?) steel pipe with cast iron fittings and this all gets pressure tested to ensure that no vapors can reach a spark. Simplify the wiring and either get explosion proof light fixtures or install thick wire reinforced tempered glass panels sealed between the light fixtures and the booth. All booths need an manometer cutoff switch for the air compressor/ supply in case the fan quits. Without a permit and a fire marshal inspection your home-owners insurance won't pay a dime and will probably cancel your policy if they get wind of a booth.

Dayton makes a 12", 3/4HP axial fan with two speeds that works well and supplies about 1600 CFM in free air. You'll need minimum 100 feet per minute so for 4 square feet of exhaust area that's 400 CFM but at least double that to account for loaded spray filters and intake filters not to mention twists and turns in your exhaust flow. I'd definitely consider having a chimney stack with a rain cap outside the window but that will draw as much attention as the lacquer smell in the neighborhood.

[Barry Daniels]

I use a 1/3 hp totally enclosed fan cooled (TEFC) motor with a spark proof, aluminum fan blade mounted directly to the motor shaft. I got if from Grainger about 40 years ago and it is still going strong. My booth has a chimney stack with a remote controlled rain cap. I don't worry about sealed wiring and XP lighting as that is outside of the booth. Make up air is provided though my fireplace inside my house which prevents vapor intrusion. I have checked outside during spraying and have never detected any lacquer odors. I think that is due to the exhaust going up and dissipating before it can get to ground level. After spraying I turn on a small bathroom exhaust fan that is also mounted to my booth to keep a bit of negative air pressure in my shop. Kind of like this:

https://www.grainger.com/product/CANARM ... nel-29NV31

[David King]

Typically those aluminum or brass spark-proof fans blades will also have a grounding brush that wipes against the hub of the fan. Most TEFC rated motors wouldn't qualify as explosion proof but are certainly better than an open frame fan motor, a "wash-down" motor would be even safer.
I would also consider an old belt driven "squirrel cage" furnace air-handler unit that could do double duty as a shop air cleaner. The most likely source of an ignition spark will be the on-off switch so that's where I'd focus my efforts - don't put it or the light switch inside the booth. Same with the switch for the HVLP pump.