Spray Booth Ventilation, Back Pressure?

      A fan that works well mounted in a window has trouble moving air through a 50-foot duct with three bends. December 9, 2010

I just installed a 50' run of 18"D clear PVC tubing to ventilate my spray booth. I have a great industrial fan that has done amazing for my last two booths when window mounted. In this case, the fan seems to be unable to accomplish full speed and the suction on the booth end of the line is insufficient. Is this a resistance to flow/back pressure situation? Is there anything I can do to get the fan up to full speed?

Forum Responses
(Finishing Forum)
From contributor C:
What diameter is your fan? Sounds like your pipe is too small. Also, I do not think PVC would meet code. Also creates a lot of static.

From the original questioner:
My fan is 26"D and it's super powerful. No info on the motor housing as to hp. We only spray waterborne finishes, so I think the PVC will work. The difference in fan performance is astoundingly better when we disconnect the duct. It just can't get going when pulling through such a long distance.

From contributor R:
How airtight is your shop? Is there enough make-up air available? Does the exhaust fan flow better if a door is open on the other side of the shop?

From the original questioner:
There isn't even a door on the spray booth yet. I've opened every door and window possible and no improvement. I even put a box fan on the booth side trying to push air through the duct work to help out the main fan, but no dice. Maybe the run is too long and the three turns in the run are creating too much resistance?

From contributor J:
For one, you have a 26" fan trying to push through an 18" pipe. Your pipe is too small. Two, every foot of pipe adds resistance; 50' and 3 elbows adds a substantial amount of resistance. In summary, your pipe diameter is too small for the length of the run.

The pipe should be made of metal. Plastic can build up static electricity, which can lead to a spark, which can lead to a boom. Especially dangerous with all the solvent vapor.

From contributor E:
I think you hit the nail on the head. 50' is a long run; add in 3 turns and that's a lot of resistance to overcome. I'm not sure if that would cause the fan speed issue. You may have two different problems here.

Can you rethink the exhaust location for a more favorable (closer) one? Generally you want your spray booth either on an outside wall for horizontal venting, or inside only if you're going through the ceiling. 50' just seems like a tough situation to make work well.

From contributor S:
Make a plywood tunnel.

From contributor J:
Take a garden hose and try to breathe through it. That is what you have done to your fan.

Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?

Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: Knowledge Base

  • KnowledgeBase: Dust Collection, Safety, Plant Management

  • KnowledgeBase: Dust Collection, Safety, Plant Management: General

  • KnowledgeBase: Finishing

  • KnowledgeBase: Finishing: General Wood Finishing

    Would you like to add information to this article? ... Click Here

    If you have a question regarding a Knowledge Base article, your best chance at uncovering an answer is to search the entire Knowledge Base for related articles or to post your question at the appropriate WOODWEB Forum. Before posting your message, be sure to
    review our Forum Guidelines.

    Questions entered in the Knowledge Base Article comment form will not generate responses! A list of WOODWEB Forums can be found at WOODWEB's Site Map.

    When you post your question at the Forum, be sure to include references to the Knowledge Base article that inspired your question. The more information you provide with your question, the better your chances are of receiving responses.

    Return to beginning of article.

    Refer a Friend || Read This Important Information || Site Map || Privacy Policy || Site User Agreement

    Letters, questions or comments? E-Mail us and let us know what you think. Be sure to review our Frequently Asked Questions page.

    Contact us to discuss advertising or to report problems with this site.

    To report a problem, send an e-mail to our Webmaster

    Copyright © 1996-2020 - WOODWEB ® Inc.
    All rights reserved. No part of this publication may be reproduced in any manner without permission of the Editor.
    Review WOODWEB's Copyright Policy.

    The editors, writers, and staff at WOODWEB try to promote safe practices. What is safe for one woodworker under certain conditions may not be safe for others in different circumstances. Readers should undertake the use of materials and methods discussed at WOODWEB after considerate evaluation, and at their own risk.

    WOODWEB, Inc.
    335 Bedell Road
    Montrose, PA 18801

    Contact WOODWEB

  • WOODWEB - the leading resource for professional woodworkers

      Home » Knowledge Base » Knowledge Base Article