Fan for spray booth (again)

[Steven Smith]

I know this topic has been discussed at length but I have finally reached the point where I can build a small spray booth in my shop and I'm trying to determine the size and type of exhaust fan I need. I have been spraying outdoors or spraying a single coat inside (with respirator/equip turned off) at the end of the day then leaving and locking up for the night. It isn't working well and nitro makes the shop stink for days. I'm ready to empty out a small corner of the shop and build a spray booth.

My spray booth will be about 5' x 6' and I intend to use some plastic-wrapped panels for part of the structure so it won't be full-depth except when it's in use. In other words it won't be a real room and I won't be able to make it completely air tight although it will have walls, doors, and a ceiling. I will probably only spray one instrument at a time and will be using both water based and traditional nitro lacquer. I plan to filter both incoming and outgoing air.

I am ready to put up the bucks for an explosion proof fan but just don't know what CFM I need or who might be a good supplier. My shop is a brick building with a hip roof so I've been looking at roof ventilation units in the 12" and 14" sizes.

Hope you guys have some good ideas - you always do <g>.

[Steven Smith]

I must have phrased my question poorly. Has anyone here built their own spray booth? How do you ventilate it?

[John Hamlett]

I'm getting ready to build one. I have a DeVilbis explosion-proof fan that is belt driven, and I plan to just go through the wall with it. I got the fan at an auction (for $5!), so I don't really know much about it (model, CFM...). I assume that, by using different size pulleys, I could adjust the fan speed and thereby the CFM. I've seen fans similar to mine used in conjunction with duct work that directs the exhaust up. In more populated areas than mine, with neighbors in sight, or in your case with brick walls, that would probably be a good idea.

[Steven Smith]

$5 is basically free, what a great deal. I just found a used 12" Dayton hazardous location fan and bought it but paid $250 for it. it's a direct drive version and should be relatively easy to vent up through the roof.

[Tom Parse]

I built this unit about a year ago... No need for an explosion proof motor. I got the idea from a fish carver site... you can see the video here. It cost me about $100 to build and it works great.
http://video.google.com/videoplay?docid ... 9945&hl=en

[David King]

The rule of thumb for a spray booth is that you want air moving at about 100 feet per minute so you divide your exhaust fan capacity by the square footage of exhaust filter and try to shoot for 200 cubic feet per minute (CFM) per square foot of plenum opening to account for your filter loading up with spray mist and any losses of air flow ("static pressure") going up the stack (exhaust pipe or chimney). Intake air is very important and you want to have 4 times the filter area of intake air as you have in exhaust filter area. If you have a plenum opening that's 2' x 4' -you would want 32 square feet of intake air area.

As an example, you have a 12" explosion proof fan rated for 1000CFM. You can have a filter area of say 20" x 40" (filter pads come 20" x 20") which under the best circumstances will give you a flow rate of 1000/(800/144)= 180 FPM. Your 5.5 square feet of exhaust filter area will want to be matched by 22 square feet of intake filter area.

What most folks don't like to worry about is "make-up air", i.e. heated and conditioned air that will come into the booth at the same rate as you are blowing the smelly air out. You need to leave your shop doors and and windows open or you will quickly drop the flow rate to a trickle.

[julian gifford]

I built this unit about a year ago... No need for an explosion proof motor. I got the idea from a fish carver site... you can see the video here. It cost me about $100 to build and it works great.
http://video.google.com/videoplay?docid ... 9945&hl=en

Thats a pretty cool idea. What are the dimensions of the booth you built to spray guitars?

I've been spraying automotive 2k, hanging the guitar from a tree in my yard. I notice I use a very large area to clear the entire guitar in one session. Having a setup to spin the guitar front/side/back/side would cut down the room necessary.