Fan for a spray booth

[starmanmm]

Ok.... so I am looking at building a portable spray booth and my question is this.... what should I be looking for as far as CFM are concerned? I have found a fan with a CFM rating of 160 ans was wondering if that is enough?

Ok... so I have another question... what is the usual CFM rating on the fan for a store bought unit?

[Division_6]

This link might help with question #1.

[starmanmm]

Nice site.

[skymods]

I built my own booth and that site was extremely helpful. I wish some of the explanations and examples were a bit easier to understand. It's the ductwork that kills the working velocity.

My booth is 16"x20". My fan is rated at 273 CFM and I bought is at Grainger http://www.grainger.com/product/DAYTON-Blower-1TDR3 but if you look around you can find it cheaper. I just happen to be very close to a Grainger store. My ductwork is about 2 feet long with a 45 degree bend.

I'm very happy with my choice of fans.

Dave

[starmanmm]

The plans that I am using are not design to vent outside but into a bucket with charcoal filter and furnace filters.

One thing that puzzles me... if the fans cost that much, how can they sell those portable spray booth for those prices?

[skymods]

You need to look at the CFM. Those inexpensive booths all over ebay have a very low CFM, somewhere around 100 and that drops even lower as soon as you add any ducting.

[markcan]

Ok.... so I am looking at building a portable spray booth and my question is this.... what should I be looking for as far as CFM are concerned? I have found a fan with a CFM rating of 160 ans was wondering if that is enough?

Ok... so I have another question... what is the usual CFM rating on the fan for a store bought unit?

Here's the one I used in my homebuilt booth. It's a marine bilge fan that has a sealed motor since it's used to vent gasoline vapor. That makes it ideal for spraying lacquer-based paints or other flammable stuff. It needs a 12v power supply, so I had a friend who's good with electronics come over and hook one up for me. Blows like a hurricane.

http://www.ebay.com/itm/BOAT-MARINE-BLO ... de&vxp=mtr

[splake]

I bought two Dayton Blowers off of Amazon. I have a double blower booth. I followed the CFM formula posted here on the sight and take things into account like Flex lines bring down CFM's. They were expensive $136 a piece and I had to use my jigsaw to make a couple of flat 1/2 plywood adapters so I could mount it to my plywood box, but they are worth it.

Splake

[starmanmm]

Ok... based on the website....

My design is Cross draft design

The rules of thumb -- design cross draft booths with 100 FPM face velocity

Cross-draft CFM = inside height x inside width x desired face velocity (depth is not a consideration)

For example, the inside height and width of my cross draft booth is approximately 18" x 24". To calculate for industry standards, multiply the height and width by 100 FPM:
1.5’ x 2’ x 100 FPM = 300 CFM


SO

My container measures 22” x 15” x 13”

1.10 x 1.3 x 100FPM = 143CFM

So, then the fan that I have is 160 and that should work... I guess.

but like I said, the fan does not seem to do too much in my opinion.

Thoughts?

[AZ]

I don't see in your calculation where you've included the loss due to the static pressure associated with pushing the air through the duct work as explained in the latter part of the referenced article.

Note, when I built mine using the information in the article, I opted for a downdraft design since I could get by with a fan with fewer CFM than what would be needed for a cross draft design.

[starmanmm]

Correct, I did not include the calculations for the pipe.... I was focused on the cross draft requirements.

I am still confused why the fan I have, rated at 160 CFM doesn't seem to do too much as a draw? Would the squirrel type do a better draw?

[jackshield]

No calcs, just pics. Made a couple of generations before the current. The first one for under $20. I also have a pair of the bilge blowers I never used if anyone is interested.
http://s300.photobucket.com/user/jacksh ... t=3&page=1

[starmanmm]

Ok... the saga continues....

Now this is more for the newbies out there to LEARN FROM MY MISTAKES!!

I had purchased a 240 CFM Boat Marine Blower Fan/ Bilge Blower 12v 4" ( http://www.ebay.com/itm/Boat-Marine-Blo ... 0e&vxp=mtr ). I figured that if it could handle gas fumes then paint fumes shouldn't be an issue.

Forget it.

This is what I have learned today (yes, I tested it out today by priming a piece with a rattle can primer).... CFM are important but so are the RPM's!!!

Without the RPM's in the 1,000's you will not get the draw to pull the vapors out of your booth.

I sprayed a test piece in the basement and my boss, she tells me that she can smell the primer, somewhat, in the kitchen.

So, yes, this was a failure.

I have no idea what the RPM's are for this unit. That info is not found on either the unit or the box. So, I have no idea what it is spinning at.

So, my advice is this... that although CFM's are important, you will also need the high RPM's to move the air out of the booth as well.

Ok, back to the drawing board.