Official Luthiers Forum!

I have been battling with trying to get my spray booth to work forever. My first question is, is it important for there to be a lot of fresh outside air coming into the shop? I have a 4'x4'x4' box that is built and is on a frame that lifts it up about waist high. A 24" fan is mounted in the back of the box. I have a fan shutter installed in the wall. The problem is that I have to have three windows open or a door for it to work. If I don't have a LOT of air flowing inside the shop through the windows or the door, air is sucked in all around the edge of the fan and the spray exhaust is blown in the shop. I have thought about attaching a big pipe to the fan and sealing the other end of the pipe in a piece of plywood covering the shutter. If I didn't have much fresh air intake would it work like this? Or could air actually come back through the pipe because of the sucking air pressure inside the shop. Whats the point of having a spray booth if I have to have tons of air flowing through an opened door on a very hot humid/cold damp day? Do you guy's have to open doors/windows when you turn on the exhaust fans? My fan is smaller than the shutter because the shutter replaced a window. Even though the shutter is opened fully I think this maybe causing my problem with the air sucking in around the fan. I'm starting to think that attaching a pipe would solve a lot of my problem. Any info on this would be greatly appreciated.

Here are some pics so you can hopefully figure out somewhat what I'm talking about.

Colby,
I notice in the picture that the fan motor is in the path of the exhaust.
You didn't say what you are spraying-if it is nitro or anything simmilar this can be a recipe for disaster!!
One spark and the fumes could (and will) ignite.
Brad

    Your set up needs air flow in and out. that fan is DANGEROUS if you are spraying flammable material. I suggest you take care of it first.
     You need an explosion proof fan
john hall

Colby --
there has to be a make-up air supply or the pressure imbalance between the outside and inside of the booth will either find an air supply or stall your fan or both.   It looks like in your case the best bet is to make a filtered intake.    

I hate to think of the electricity that goes into one of those commercial booths that uses conditioned air and huge banks of lights.

you also need to connect the fan flange to the vent. note also the comments of others re using the non-hazardous duty fan with nitro!

ideally the booth should be in a spray room which has a filtered air supply.crazymanmichael38566.0727546296

Colby, I think you are moving too much air. Your gun probably only uses a couple of CFM and I`d hate to think how much air that fan moves. It must be like spraying in a hurricane. I go to lots of trouble and expense to de-humidify my shop here in East Texas and would not think of opening a door or window because of blushing problems.I`d suggest a lot less fan and one that is explosion proof! Good luthiers are hard to come by!

   I just built one for my shop. I used a fan system from a hot air house furnace. this move alot of air. I made my booth 5 feet square.
   The back wall is all filters and I have 2 6 inch air hoses ducted to the outside. The door has 2 filters in it to let air in.
   

One thing you can do to get by the explosion proof fan issue is to set a motor/belt drive system. That way the motor could be outside the system and you'd only need a small slit in the ducting for the belt. That would also allow you to gear it down to move less air.
Normally I'm not all that worried about explosion proof fans but seeing as you are spraying directly into it with little duct work for the paint to dry in the air, I think you are asking for big problems with that setup.

Tippie,

You said the door has two filters in it to let air in from outside. Do you mean a spray booth door that lets air in from the rest of the shop, or are you getting air intake from outside?

I know the fan is not explosion proof. Right now I'm just spraying waterbornes.

i should have mentioned that there are figures published and available online relating fan capacity to the filter area of the booth. as was mentioned above too much fan and you will waste finish, too little and the overspray just hangs around.