Need some ventilation systems advise
I taught fluid power which included hydraulics & pneumatics, but never covered or researched ventilation systems.  I have purchased two hoods to go over my welding bench each one is about 2 feet wide and 6 feet long.  I want to add a ventilation system to exhaust the fumes & dirt/crud outside.  I also don't want to have hurricane force winds! Yikes   So I'm looking at purchasing two of these fans:

One of the major advantages is they are 12V DC so I could regulate the fan speed and thus the CFM.

I could also cross connect the hoods and just use one fan.

Your advise/comments will be appreciated.

Here is another possibility:
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If you go with one fan, be sure to put dampers in both ducts, so you can block off the one you aren't using to keep from sucking too much room air outside.

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For what it is worth....

I installed a common kitchen range hood over my bench to vent out fumes from my lead furnaces. I bought the heavy duty unit with similar sized dual squirrel cage fans in it - one on each side of the hood. The fans have an adjustable speed but they run at the same speed, they are not independently operated.

In use the hood sits roughly 24 inches over the top of the lead furnace(s). Even at full speed I found fumes from the furnace would spread out and find their way around the outside portion of the hood and build up at the "ceiling" instead of getting vented outside. The smallest amount of "cross wind" would deflect the fumes away from the underside of the hood and they got missed. I had to add cardboard panels to the sides of the hood to extend it downward so the fumes could not escape before being caught in the draft and expelled.

Once I tried using it while doing some MIG welding. Same thing. Unless you are DIRECTLY under the hood and in close proximity, the fumes will get away from those small squirrel cage fans. STICK welding is right out with the amount of smoke and fumes produced. Personally I would opt for your second choice and go with the larger 10" filter fans. Even better: At my old house I worked in a storage shed that I installed a 24" gable fan in and that worked a treat with the roll up door open at the other end. Can't do that in my current basement though. Sad

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I installed an air to air heat exchanger for a house. Used a washable furnace filter on the intake. No hoods or ductwork, other than the outside inlet and exhaust. Works pretty good. Without it on the shop is a yellow haze when using the plasma table.
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Back in high school shop class we'd go into a welding booth and strike an arc to have a cigarette. When we were done we'd flick the cigarette up into the hood and it was gone outside somewhere. It had some really good suction!
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I picked up an old Jennair fan from a customer. Used it to build my 4' x 4' welding hood. Not too loud and moves a lot of air. No hurricanes, though.

If you want to control a DC motor, I'd suggest Pulse Width Modulation, rather than mere voltage reduction. Make sure the PWM unit runs at a frequency above audio. Keeps you from hearing the pulses.

If you can't get one, make one.

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(05-05-2020, 08:41 PM)Vinny Wrote: Back in high school shop class we'd go into a welding booth and strike an arc to have a cigarette.  When we were done we'd flick the cigarette up into the hood and it was gone outside somewhere.  It had some really good suction!

Sounds much like what we did on the Coral Sea.  The tool room/lounge had a hatch that opened up to one of the uptake spaces (think chimney for one of the boilers).  We'd crack open the hatch when ever we went on a "smoke break" also served as an emergency disposal unit in case someone was approaching.
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Checked with a PE friend of mine.  I need 1500 CFM in each hood and I found some exhaust fans that will do the trick.  Thanks to everyone for the replies.
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