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How much ventilation

How much ventilation (post #162111)

eric on Sun, 02/20/2011 - 19:54

Workshop

Hey guys and gals,

I am building a new ~900 square foot workshop under a three car garage using pre-cast concrete planks.

I've got three concerns I am trying to work out: dust collection, humidity, and fresh air ventilation.

I think I have the first 2 figured out, but am struggling a bit with finding a source for how much air movement I will need to ventilate the shop when finishing. I have enough places to get in some ducts to the outside, but how much airflow should I aim for?

For less than $300, one can buy "barn fans" at McMaster.com that can move anything up to 4000-5000 CFM. How much is too much? How much is not enough?

Would love to hear your thoughts.

Cheers,

Eric

air (post #162111, reply #1 of 3)

by RalphBarker in reply to eric [original] on Fri, 03/04/2011 - 07:58

I'm surprised your question has gone unanswered. I'm certainly not an expert, but here are my thoughts.

First, "enough ventillation" probably depends on which finishes you are applying, and how. Spraying, particularly with highly-volitile finishes, can become quite complicated. Not only do you have to be concerned about getting rid of the "bad stuff", but also about not passing it by a source of ignition (like a fan motor). For normal ventillation, I'd think in terms of volume, and how quickly that volume is replaced with fresh (or, conditioned) air. There are certainly industrial standards for this. How closely one wants to follow the industrial standards in a home shop is the question.

For example, with 900 square feet, and assuming an 8-foot ceiling, your volume is around 7,200 cubic feet. One rule of thumb for a photographic darkroom is to be able to replace the air volume within a two-minute time span. That time period can be lengthened if the venting is more localized - e.g. the vent is over the source, so the "bad stuff" is pulled directly.

Another point of concern is where the "replacement" air is coming from.

Depends on the finish (post #162111, reply #2 of 3)

by AutumnWoods in reply to eric [original] on Fri, 03/04/2011 - 20:41

If your using wipe on varnish, shellac, oil and wax, or the like I wouldn't be too concerned. A nice steady replacement stream of air should do you. If your using finishes with a high VOC count and strong carcinogens like lacquer, catalyzed laquer, conversion varnish, epoxy, etc I would get that stuff out of there! By which I mean as much ventilation as physically possible. But I also have a bad sensitivity to it because of overexposure early in my career. When I'm around it too much I start to notice drowsiness, mood swings, irritabilty, etc. After I left my last cabinet job as a finisher I noticed the onset of mild withdrawal symptoms. And this was coming from a well ventilated spray room using a high end North Safety respirator. Just the stuff absorbing through my skin and eyes can get to me. All thanks to my first woodworking job at a furniture repair shop where we sprayed lacquer all day with nothing but a floor fan and a man door to ventilate a 3,000 sq ft warehouse. They broke about every safety reg in the book, including not providing us proper equipment or letting us know that the fumes would eventually fry our brains. Sure am glad I moved on to better things.

Short answer: As far as I'm concerned you can never have enough fresh air no matter what your using. The fumes from most finishes can effect your brain, even if they just effect your concentration. Your mind is your most valuable tool and deserves to be taken care of.