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  1. #1
    Join Date
    Mar 2014
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    can a higher merv rating affect airflow??

    Do high merv rating affect air flow? Or its not noticeable??

  2. #2
    Join Date
    Aug 2001
    Location
    Pavilion, NY
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    The higher the merv the more restrictive the filter. The more restrictive the filter the less the airflow in most situations
    ...

  3. #3
    Join Date
    Aug 2010
    Location
    West Monroe, LA
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    Depends if you have proper return and suppy for the system. As stated the higher the merv rating the better the filter filters the air but the trade off is decreased air flow when the filter gets dirty.

    How they market higher merv filters is how they can catch more particles when returning but fail to tell people the flip side reach is decreased air flow once dirty. Most homes are lacking in the supply and return do to rules of thumb for sizing ductwork and equipment take a undersized return and add pleated filter with a high Merv and you will have a big problem.

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
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    Quote Originally Posted by wantboost View Post
    1. Do high merv rating affect air flow? 2. Or its not noticeable??
    1. Yes.
    2. Absolutely Noticable.

    Any 1" pleated filter of a normally selected area will be detrimental to
    system performance and equipment life if it is > MERV 7.

    dP filter new is probably about 0.2" when face velocity is > 300 Feet Per Minute
    dP filter dirty would be 0.3" or 0.4"

    Relatively speaking, that's in the range of 50 to 80% of the blower capacity.

    MERV 8 EXAMPLE
    HOW NOT TO DO IT.!
    http://www.flanderscorp.com/files/Fl.../VP_Merv_8.pdf
    BASICALLY USES 0.2" AS SELECTION CRITERIA
    ........................

    Correct: USE 0.1" dP in SIZING Filter Area

    3 ton requires 1,200 CFM
    20x25x1" 1042 CFM 0.22" <-__ _Flanders Data for MERV 8_

    USE TWO FILTERS in parallel so that the dP << 0.1" NEW
    --- Half the rated flow rate will provide about 1/4 of the dP ---

    Otherwise, 2", 4" OR 5" filter depth SHALL BE used for any > MERV 7 filter.
    http://www.flanderscorp.com/files/Fl...t40LPD_web.pdf
    24x24x2" 1200 CFM 0.11"

    MERV 7 Resistance is Too High ( > 0.1") for 1" Pleated at velocity > 180 FPM
    http://www.bettymills.com/product/mo...E_EconoPlt.pdf
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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