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Old 2007-06-14, 9:59am
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BlueBetween BlueBetween is offline
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Join Date: Jun 11, 2005
Location: Edmonds, WA
Posts: 1,119
Default Please Help my with my vent design - it's not working.

Please help me figure out why this isn't working - I don't know what to try next.

This is my vent hood - an upside-down washtub. It has 8 inch vent pipes and the fan is on the other side of the wall. It's 24 inches above my table, 18 inches above my torch. Incense test failed - the smoke just wafts about going here and there and eventually most of it goes up.



The fan is this one from grainger:
Blower,495 CFM,115 V
Shaded Pole Blower, Air Flow @ 0.000 Inch Static Pressure 495 CFM, Speed 1570 , Voltage Rating 115 Volts, Power Rating 225 Watts, Current Rating 3.25 Amps, Frequency 60/50 Hertz, Thermal Protection Auto, Wheel Diameter 6 1/4 Inches, Wheel Width 4 1/4 Inches, Air Flow @ 0.100 Inch Static Pressure 476 CFM
Grainger Item # 4C445

The fan box looks like this, except it has 3 extra 2.5 inch holes drilled in the bottom of it to provide air to the motor:





The make up air - door open or shut, same deal. I also have the vents in the wall above the table, behind the hood, I've tried them open and shut, doesn't seem to make a dif. We've gone over the whole system, it's all screwed and taped tight.

I tried adding some back and side baffles, no help. The fan seems to be exhausting strongly. I tried blocking part of the vent hole in the hood and it grabbed right on to the hard plastic sheet I had and held it up by itself.

I called grainger and the tech guy there suggested I change to 6 inch pipes. Dale says that info is incorrect.

I don't know what to look for next. Please, any ideas?

Thank you.
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