How do you determine CFM through ventahoods?
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  1. #1
    Join Date
    Jul 2004
    Location
    West TN
    Posts
    983

    Question

    I dont' work with vent a hoods much and would like to know more about them.
    I know there's not alot to them, but I figure the more I know the better tech I'll be.

    DOes anyone know where I can find info about checking the CFM through a vent a hood system?

    I'm wanting to know how to check CFM so I dont' have a major positive/negative pressure on building.
    Especially if I question wether someone has tinkered with split sheaves on the blower motors pulley.

  2. #2
    Join Date
    Mar 2004
    Location
    Vancouver, BC
    Posts
    125

    Vent hoods

    My normal rule of thumb is to take the exposed perimeter length and multiply by 100CFM/foot. Example: a cooking line hood with a wall behind it, open on the two ends and front face: 2.5 feet plus 2.5 feet plus 6 feet long = 11 feet x 100CFM = 1100 cfm minimum. Depends on the type of thing being exhausted- some folks will use 125 cfm per foot to be safe. Normally the hood supplier should have minimum CFM ratings on it for compliance to NFPA-96 and UL.

  3. #3
    Join Date
    Jun 2004
    Location
    Eugene, Oregon
    Posts
    1,018
    If you know the rpm and static pressure you can use the fan curve to estimate cfm.
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten". --Benjamin Franklin
    "Don't argue with an idiot, they will drag you down to their level and beat you with experience". --Mark Twain
    http://www.campbellmechanical.com

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