Paint Booths - Model Railroader Magazine

Hey Mike:

I'll post these pictures over at the Barn too and as mentioned there, I build a booth a few years ago, but I saw this thread and thought I would jump in.

When it comes to moving paint fumes and over spray...Is there such a thing as "over-kill"? About the only thing that can go wrong with moving too much air is that you won't be able to get enough "make-up" air or the volume and speed of the moving air at the point of painting will cause the paint to dry on its way to what you are painting or ZOOM right past it.

Here is a rule of thumb in regard to the sizing of the blower: When using organic solvents, OSHA recommends an air flow of between 100 & 200 cfm (cubic feet per minute) at the point of spray, or in my case, at the level of the painting table. Two things determine that air flow; one being the size of the booth opening and the other being the capacity of the blower; the two go hand in hand. The formulas needed to size one to the other are really quite simple.

1) Size of the booth opening, height x width in sq. in. divided by 144 = sq.ft.

2) Blower rating in cfm divided by the booth opening in sq. ft. = the air flow.

Here is my case scenario as I worked out the numbers with thoughts of being able to use a Dayton Mod. # 4C445A Blower capable of moving 525 CFM, which I did. 

With my 16" x 32" opening;

16 x 32 = 512 / 144 = 3.5

525 / 3.5 = 150

As for, what I felt was total safety, I installed the blower outside of the air-stream. This should also keep the motor cleaner!

A few safety tips:

1) Make sure the blower is correctly sized, installed outside of the air stream and/or has a brushless motor. (I have discovered that all the new Dayton motors are brushless)

2) Be sure to seal all joints in both the wood and metal ductwork.

3) Always vent separately, with as short a run as possible.

4) Don't have exposed lights in the spray area.

5) Be sure to have a source of "make-up" air equal to you exhausted air.

6) Over size when in doubt. Elbows and extra length in run will decrease the Air Flow. A good rule of thumb is to add 10%.