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  1. #1
    Join Date
    Aug 2005
    Location
    iowa
    Posts
    1,649

    help with exhaust fan size

    hey guys, i need some help with sizing an exhuast fan for a hood.

    first of all the hood is approximately 5' by 14'. their is a 3' broiler a 3' oven/griddle and 2 fryers. all gas.

    the problem is the exhaust fan on the roof has very little info on it.

    when i looked in the hood control compartment the most i can tell is the fan should be no more than 1.5 hp and i know its 3 phase 230 volt. (this is according to the schematic)

    on the roof the fan has a 2hp motor that is 3 phase. it is rated at 6.7 amps but is drawing 2.6, so its obviously oversized or has the wrong pulleys or something. anyway on fan i can read
    stk no 723
    nga10b
    1/3 hp

    i know that the wheel diameter is approx 14" and 7" deep.
    the curb is 24" by 24"

    so ive got a general mess. but what i want to know is... what is the correct way to size the fan? the customer is having problems with smoke roll out from the broiler. and the fan is going to need to be rebuilt due to worn bearings and shaft. i figured rather than rebuild this thing i might be better off to put in a fan that is sized correctly to handle the broiler..


    i hope this makes sense.

    im going to look over my code books now.... just wanted to see what the real brains thought!!

    jeep

  2. #2
    Join Date
    May 2012
    Location
    San Diego, CA
    Posts
    352
    Personally, I would just call any fan manufacturer and ask for information. Usually the fan size is based on the duct systems static pressure lost and RPM of the fan. See below for an example.

    Per CMC 2010 - 508.4.1.1

    5 X 14 = 70 sq. ft.

    Assuming the hood has 3 exposed sides and your boiler (gas) will require 7,000 cfm (Q = 100A). Soild-fuels will require 14,000 cfm.

    I just looked on the Captive Aire website and their 2 hp fan (NCA30FA) can hit 7000 cfm @ 650 rpm and .7 esp in ducts.

    I am not sure what code you follow in Iowa, Here in California, we have the Uniform Building Code with some additions that make it the California Building Code. Even if you are using the International Building Code, the topics are pretty similar. The hood sizing should be other the Exhaust section (Chapter 5 in UMC & CMC).

  3. #3
    Join Date
    May 2007
    Location
    Dry as a bone Tucson
    Posts
    4,343

    Thumbs up CaptiveAire

    CaptiveAire is the way to go. There stuff next to greenheck or cook is like comparing snap-on to taiwan. In other words they are flimsy as compared to the heavy duty quality of materials and construction of the CaptiveAire products. I'll never install another Cook or Greenheck product again unless I'm made to .
    Some Talk, Some Do
    "keeping condensing pressures low and evaporator pressures high"
    "Some customers are more interested in comfort than energy savings"
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