Air Exhaust System for Temporary Paint Booth

[JHildreth]

   I need to construct a “take-a-part” exhaust fan system to remove airborne paint “dust” from my collapsible paint booth.  I want to also use it when I am sanding.  I have tried using the search function, but I am not very accomplished in guessing the best key words to use.  The hits I did get generally discussed exhaust fans mounted in a window.  My setup is not conducive to this kind of arrangement.

   The current concept I am considering is a square or rectangular box (wood or cardboard) with a 4 or 5 inch tin pipe in the back.  A section of 4 or 5 inch flexible ducting would connect the inlet box to another box frame of similar configuration that would mount onto an existing 20 inch box fan.  The idea is to place the inlet box at the dust generation location and put the box fan in the doorway in the back of the garage.  The front garage door would be up either part way or fully depending on the weather.

   There are several questions in my mind about such a design.  Is the box fan powerful enough?  Are the flow losses in the 4 or 5 inch tube too large to maintain sufficient airflow?  What box area is sufficient to generate enough draft from the painting/sanding location to move the particulate material?  Must the box cross-section be tapered toward the tube end?  Where should I put the air filter; over the mouth of the inlet box or against the fan box?

   I would appreciate any comments, suggestions or even alternate designs you would offer.

   Thank you

Joe

[944_Jim]

It sounds like you want a paint box in a "comfortable space" attached to a remote draw-through ventilator. Have I got that part right? I think the 20" remote box fan may lack the horsepower to pull well.through the pipe/hose. Is there any chance you could move your "booth" to the door?

I made a cheesy 'paint booth," albeit temporary, in front of one of my attached garage windows...away from the garage roll-up door.

The box was only cardboard, and wasn't very deep front to back. The backside was opened to fit against a box fan propped in the window. A furnace air filter trapped most of the solids before passing the exhaust through the fan and out the window. By changing fan speed, I can control how much (or just enough) vapors to vent out. This is the fastest, most temporary set up.

A "Gen-II" iteration used 6" HVAC plenum-hose stuff (the silver, insulated "soft-duct") to accomplish the same thing, but tied to an old HVAC squirrel cage propped on a plywood box in the same window. Man, that thing sucks! Setup takes longer, but the vented space can be anywhere...great for pulling exhaust fumes out of the tail pipe and blowing outside!
Since the motor is outside the squirrel cage, I don't really worry about the vapors pulling through the cage and blowing out if the house...no filter required.
And it gives me the "portability" to make the paint booth or exhaust vent anywhere I can snake the HVAC plenum-hose stuff within the garage. At this point, the issue became trying to get the hose-stuff back into the box for next time! Too bad too, since it made being able to run a car in the closed garage convenient AND safe in the winter time. Talk with your local HVAC installer...I bet you could scrounge the cage from one of his furnace change-out jobs.

"Gen-III," the last iteration put the "paint booth" directly attached to the HVAC squirrel cage, with the squirrel cage still propped in the window. Now I don't deal with the plenum-hose. This one lacks portability, but tear-down is faster. The only problem with the squirrel cage is slowing  down airflow to keep from drawing cold winter air into the garage. Is any of the systems  explosion-proof? Nope...but I do feel better about the squirrel cage version since the vapors don't get pulled past the motor.

Gen-IV will probably be 4" hose pipe in a bathroom exhaust fan in the corner of the "hobby closet" that runs along the inside of the garage wall...a 22'x5.75' storage space that the hot water tank resides in. My wife banished dope in the house, but "authorized" a through-the-wall AC unit and insulation to create my "man-crevice" in that closet.

Tell.us how you finish yours!

[Gordon Van Tighem]

Whatever your decision, be sure you check the area where it will vent as the paint will spread to anything in the immediate area.
I had a friend who vented his spray booth out an extra chimney in his rented condo and then had to replace the cedar roof around the chimney outlet due to overspray.

[peabody]

On the cheap, and effective, is a 20" floor fan, square.
Then tape a 20" furnace filter to it.
Place close to the object you will paint
Run on low or medium
If you are constructing a "booth" from cardboard, works well there as well.

Have fun

[Paul Smith]

I finished-off an unused attic for that purpose.

Not just dope fumes, it blows out dust from the whole house, too.

In summer, the heat acts as an oven.

Of course, this cost me a door, stairway, lighting and some floor work.

[frank williams]

I have considered using the popup tent that I use for shade at contests, about 10x10.  I would open it on the driveway tape and drape plastic sheeting from the rim of the tent.  One continuous sheet around the perimeter.   A box fan taped in the doorway slit would provide exhaust. 

Anyone ever tried anything like this.  Just painting outside on a calm day is ok, but there is too much pollen in the air that adds to the finish?

Is a box fan "explosion proof"?  Its an induction motor I think.

[Tom Vieira]

I have considered using the popup tent that I use for shade at contests, about 10x10.  I would open it on the driveway tape and drape plastic sheeting from the rim of the tent.  One continuous sheet around the perimeter.   A box fan taped in the doorway slit would provide exhaust. 

Anyone ever tried anything like this.  Just painting outside on a calm day is ok, but there is too much pollen in the air that adds to the finish?

Is a box fan "explosion proof"?  Its an induction motor I think.

I've done this in my back yard for model rockets, worked fine.  most box fans are brushed motors, at least the ones I have...

once upon a time in high school, when my dad and I painted my Datsun 280z, we just used plastic cloth all around the garage to try and limit overspray on everything else in there, and put up screen door material from end to end of the open garage overhead door, and the back door to provide ventilation.  worked great!  even as the cotton wood was flying, VERY little dust issues, and no dye-back (common with limited air circulation and polyurethane clears).

we also hosed down the floor and used a squeegee to to limit the dirt getting kicked up as well.  you don't want to soak the floor, just get it a little damp.  same would apply to your driveway.

[Dave Moritz]

Paul: You've got a pair of slab wing beasties in your photo.  They look pretty nifty. What are they, and how will they be powered?

My apologies for some serious thread drift here if this develops into a topic.

Dave Mo...

[Paul Smith]

Paul: You've got a pair of slab wing beasties in your photo.  They look pretty nifty. What are they, and how will they be powered?

My apologies for some serious thread drift here if this develops into a topic.

Dave Mo...

Those are Sig Busters for the local "grab bag Goodyear" event.  Everybody uses Sig Busters or Shoestrings and draws for the use of a club-owned OS LA 15. 

[Steve Helmick]

A 20" box fan setup horizontal with 2x2 legs and a 20x20 furnace filter makes a good sanding table. I am not sure whether it would be better to put the filter atop or under the fan. For a paint booth, I'd arrange the box fan at the air intake and perhaps put a furnace filter on the outlet. Blowing paint presidue  through the fan motor can't be good!  Steve   

[kevin king]

An explosion proof motor is what you should really use. It's completely sealed. No air vents on the motor = no sparks from the brushes to ignite the fumes.🏃💥🔥

[Chuck_Smith]

Plastic blades are a no-no too. They build up a static charge from the paint particles.  It doesn't take much of a spark to light the vapor and then you have the atomized paint in the flow which is almost a perfect fuel.

[john e. holliday]

When I have to use a box fan to blow the paint or dust fumes out of the house I set it so it is blowing at me and if out side the fan is up wind so the wind will carry every thing on away from me.

[JHildreth]

Thanks everyone for your comments.  I now know some important issues that must be considered.

Frank Williams' booth description is exactly what I am using; the frame from a 10 x 10 foot portable shade covered with light plastic sheeting.  I erect the booth inside my garage so I can paint regardless of wind and rain.  Even though I keep the garage door open, the booth still collects some paint dust which settles on the model.  I have put up with the slight dusting till now, but I am trying to improve my finishes and the dust needs to go.

I guess I'll visit an A/C business or two and see what suggestions they might have relative to an appropriate fan.  I might even find some scrap components I can use.

Thanks again.

Joe

[Bob Reeves]

If you really want to move some air salvage the squirrel cage fan out of a AC/furnace. It will probably be a capacitor start induction motor and you might get lucky and be able to pick it up for free. I have one that was the result of a friend replacing the heat/AC unit in his house.