I am in desperate need of some technical help for fan and filter configuration/selection for my spray booth. I am a woodworker and have built an enclosed spray booth with dimensions 5’w x 9.5’ h x 8’deep (380 CF). The entry door is 5x6.5’. The physical booth is finished and immutable. It’s a smallish booth but I rarely build anything bigger than 3-4’ wide. Replacement air is from outside and unlimited. I only spray when its >50 degrees outside. No neighbors to worry about disturbing.

My goals are:
1) To keep most of the large dust from my shop out of the booth.
2) Generate a cross draft of 100-300 FPM to carry off overspray.
3) I only spray waterborne but will get an explosion proof fan in case I want to upgrade the booth in the future.
4) Don’t let perfect be the enemy of very good.

My current plan is to:
1) Place approximately 12 SF of MERV 1 panel filters in the door (SP of 0.07” at 300 FPM) as my inlet.
2) Place a Canarm explosion proof fan in the wall opposite wall centered about 4’ off the floor (20” blade, 1/3 hp motor, 3640 CFM at 0” SP and 3140 CFM at 0.25” SP).
3) Build a plenum in front of the fan with a bank of polyester overspray collection filters 12 SF (SP of 0.1” at 300 FPM).

My questions (finally):
1) Does anyone have concern about this fan? There are a number of things that I like about the Canarm fan, but I am concerned about the SP max of 0.25”. That does not seem like much of a margin over the 0.17” SP of the combined intake/exhaust filters. The Canarm rep told me that these fans are often used for spray booths but could not answer specific questions about booth design. A second option is a Dayton tubeaxial fan with ¾ hp motor and 3112 CFM at max SP of 0.5”, but I prefer the direct drive config of the Canarm.
2) Are my filter banks large enough? At 12 SF I calculate that the main cross draft should be about 260-300 FPM. I could make these larger if needed.
3) Any issues with my filter selections? I was just going to get these from Grainger.

I am grateful to those who made it this far! I have scoured the web and can’t answer these final questions and will be appreciative of any help you can provide.

I have no expertise in spray booth design but I have had the experience of before and after spraying with adequate ventilation.
I took over shop space with a home built "booth" that I used with a 1/2 hp louvered Canarm fan for exhaust. No plenum or filters and the booth was open faced. It was loud, and clouded with overspray. Turbulent fast airflow drew dust into the finish.
I bought a devilbis plenum - 7' x 7' with a 24" - 3/4 hp fan. I use cardboard paint arrestors. The difference was dramatic even though it remains open. The airflow is slower but moves more evenly through the whole area. The overspray is quickly evacuated and dust in the finish is gone.
Some of the improvement was due to other factors; I changed my spray gun and I wear static free coveralls but I think most came from more air moving more slowly.
For reference my fan moves about 7000 cfm.
I would look for a used booth fan and plenum with a big filter area right to the floor.

also why do think you need an xp motor. and the cost of wiring and xp wiring?
that is overkill way overkill

height x width x 100 fpm.

why a direct drive fan, belt driven tubial axial fan

most mfg of booths go for at least 3/8'' sp, but have youfigured ur static pressure thru the duct?

invest in variable frequency drive, best thing u can

also ur booth is to small, you should have at least 24-36 inch before the exhaust plenum and ur side walls. you need some dancing room around ur parts. also the closer to the exhaust plenum the more velocity, ur fan pattern will be bending and u will need to jack up ur pressure to overcome the velocity if you don't have spacing from ur exhaust wall

Thanks to the responders. I agree that my booth is too small, but I have to make due the best I can with the space I have.

In response to Herb Johnson

"most mfg of booths go for at least 3/8'' sp" Does this mean a fan that can handle at least 3/8" SP drop? The exhaust will go straight outside to my farm, no duct.

How will the variable drive help me?

"you should have at least 24-36 inch before the exhaust plenum and ur side walls. also the closer to the exhaust plenum the more velocity, ur fan pattern will be bending and u will need to jack up ur pressure to overcome the velocity if you don't have spacing from ur exhaust wall." Can you please elaborate here? I don't understand about 24-36" from the side walls. Most plenums I see extend across the back of the booth. I also don't understand about jacking up the pressure. What pressure are you referring to.

Thanks, Jim

most mfg of booths go for at least 3/8'' sp" Does this mean a fan that can handle at least 3/8" SP drop? The exhaust will go straight outside to my farm, no duct answer it means that the fan can still provide the cfm when faced overcome 3/8'' s p. or simplified, resistance of duct run etc. it sounds in case their will be very little to no drop. what that also means is that without that resistance, the cfm wll rise. you would need to look at a fan curve to actually see the actual cfm at zero sp.

vfd or variable speed drive, think of this as a wall dimmer, you can adjust the fan to the speed that you want, from almost dead stop to full bore. meaning you want enufspeed to take the vapors away and provide proper airflow. sometimes you can slow the fan down to move some air across thepart to help drying without skinning over the surface of the film build.

are you just buiding an exhaust plenum? if building a 3 side booth, top ceiling panels and two side wall, then the spacing is to move around and also not to create a funnel effect going into the exhaust plenum.

one other point, i would look on line and or build in metal a perforated metal plate in front of the exhaust fan., reason, the restriction will create a bit of restriction for the fan and force fan to draw from top bottom and both side of ur exhaust plenum.

again why an xp motor, it really isn't xp for unless you install a filled and sealed connections and wiring, it really isn't xp along with xp switches and disconnects.

one way to do this that might save you money is get a exhaust fan and belt driven motor, and mount it on ur outside wall. with a disconnect.

the closer to the exhaust wall/fan the higher the velocity.what i mean by increased the pressure is ur air and fluid pressure because with higher feet per minute movement, the more velocity you need out of ur gun to overcome the pull of the fpm of the fan.

feel free to ask if you need, will try and help as i can

good luck herb j

also, one other point, i would go with standard 20-20 filters, and i would say twice as many sq ft as exhaust filter sq ft, you want the intake air slower than exhaust to minimize dust. merv 1 is not the choice. intake filter called ring panel filters, tackified on discharge side, not intake side, most are installed incorrectly, ring inside helps seal the fitter opening...a case of 20 ring panel filters which are polyester is about 100 dollars plus freight. i would also install filter grids for the exhaust filters.unless ur going to with exhaust roll filter media

One of the most important design things to consider is where the air is moving. Look at your space. You want the intake air to start high on a wall(the dust is on the floor). You want the air moving down towards the fan, which should be mid wall or lower(I like lower) Where are you going to stand? Which way will you mostly be pointing the gun? You want high volume low speed air movement. Proper spray room exhaust fans are large and spin slowly.

Thanks all, this is really helping to firm up my design, but a few clarifications please.

Re the "20x20 ring filters" I am struggling to find these online. Herb, could you please point me somewhere? Also, would these be for intake and exhaust or just intake?

Re the "perforated metal plate in front of the exhaust fan", Herb, could you point me some where or say more about it? I have a welder and some metal fabrication tools so could probably build one. Would this add additional SP drop?

Re Adam's suggestion to have the air moving down towards the fan, why is that? My original plan was to have the intake filters at the same level as the exhaust plenum, both about 5x4 ft, with the fan in the middle of the exhaust plenum. Once I build the exhaust plenum, I will be able to do velocity tests with various intake filter configurations to figure out what works best.

Thanks, Jim