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Old 2007-03-02, 5:06am
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MikeAurelius MikeAurelius is offline
Safety ALWAYS
 
Join Date: Jun 10, 2005
Location: Sauk Rapids, Minnesota
Posts: 2,401
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Ok -- your problem is manyfold --

1) get rid of the flex ducting. You are probably losing better than 50% of your air movement due to turbulence.

2) You are reducing the size of the duct right at the hood (and you hood is nowhere near large enough). This causes severe reduction in airflow. Ducts should never be reduced in size in the direction of the airflow, they should always increase in size if necessary.

3) Adding a 2nd fan on the same line does nothing but cause the two fans to fight each other.

Here's what I'd do:

1) Get rid of that small hood and use a modified kitchen range hood (modified to remove the fan and filters, and opened up on top to allow the mounting of a duct starter ring.

2) Replace all the flex duct with smooth sided galvanized ducting, at least 8" in diameter.

3) Use one fan at the window, properly sized for the hood you are using (100 to 125 CFM per square foot of hood coverage).

The reason your set up worked before is probably because you used a far shorter run of ducting. The flex ducting only gets worse in its air movement capacity the longer it runs.

The open window 25 feet away is fine as long as there is no closed doors inbetween your hood and the open window.
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Chaotic Glass: Safety for the glassworker, and random thoughts and opinions on the state of the glassworking world
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