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Question about exhaust fan placement in the line and how it affects CFM

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  • Member since
    April 2019
Question about exhaust fan placement in the line and how it affects CFM
Posted by Crimm on Wednesday, April 17, 2019 2:35 PM

Hello,

My father and I are in the process of turning a spot in the basement, into a working area. This is going to include a space for airbrushing and model kit stuff. I'm going the plastic-bin-with-an-AC-filter route, which will be ducted to the outside. It'll be my first time air brushing so, I'm starting with something inexpensive.

I've been looking into it for a while, but for the last couple of weeks I've been reading posts and blogs and whatnot, and I keep going back to Klaus Raddatz's writeup (http://www.modelersite.com/Abr2003/english/Spray-booth-design_Eng.htm), which has great technical info, but I'm a bit unclear on some of the reasoning behind some of it.

The short version is basically, where should I actually put the fan in all of this? Up against the box, or at the end of the ventilation? Let's say I need 200 CFM in the box itself (not true, just a nice round number). Should I get a fan that meets 200 CFM and put it right against the box, or should I get a more powerful fan and put it at the end of the line, which will peter down to 200 CFM by the time the airflow gets to the box? I guess one of the things I'm unclear on is what rate the airflow drops off at.

If you need more info I can provide, I just don't want to dump too much at once if it's not necessary. The bare-bones info is that my box is 12 inches by 20 inches, and my hypothetical duct-work would be an equivalent to 14 straight feet of rigid duct.

(Also, as an aside, do people have a safe way to lower the CFM if it's too much for the airbrush, or do you just up the pressure of the airbrush to overcome it if needed? I may be totally overthinking all of this, I want to make sure it's venting out safely but not unnecessarily overpowering the paint and sucking it up before it lands on the part, but I'm not sure how large that margin is. Sorry if this is too much at once.)

  • Member since
    November 2018
Posted by oldermodelguy on Friday, April 19, 2019 8:16 AM

A little more cfm is better than too little. You can always double up on layers of filter if you think it's too strong, which is unlikely. You also can spray nearer the opening to the booth rather than deep in it too...

  • Member since
    April 2019
Posted by Crimm on Friday, April 19, 2019 9:03 AM

I think I'm vastly overestimating the amount of resistance in the duct.

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