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  1. #1
    Join Date
    Feb 2010
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    Long Beach, CA
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    105

    Default HVAC Filter location

    I've never seen it or heard about it but after today I can never say "The filter is always before the fan" because there it was at the outlet side of the horizontal furnace tucked in a filter housing within the duct box. Who's seen that?

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  2. #2
    Join Date
    Oct 2010
    Location
    Southwest US
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    585

    Default Re: HVAC Filter location

    The filter is there to protect the system, not to protect the occupants. That needs to be corrected.

    END GLOBAL WHINING

  3. #3
    Join Date
    Feb 2010
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    Long Beach, CA
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    105

    Default Re: HVAC Filter location

    I should have removed the fan cover just to see the filth.


  4. #4

    Default Re: HVAC Filter location

    One of the issues this arrangement presents is excess resistance to the blower fan. The system will be less efficient and there will be more strain on the blower motor than was intended.


  5. #5
    Join Date
    Jul 2010
    Location
    Tennessee
    Posts
    60

    Default Re: HVAC Filter location

    Not only is this system not properly filtered it is paternally creating a situation where the fan motor can be overloaded. The load on a motor trying to "suck" a vacuum drops off as the air supply is restricted, as when a filter is filling with debris. When the fan motor is required to maintain a head pressure (trying to push air through a filter) the motor load increases as the filter becomes plugged and the motor is trying to maintain increasing head pressures.


  6. #6
    Join Date
    Aug 2011
    Location
    Bennett (Denver metro), Colorado
    Posts
    1,394

    Default Re: HVAC Filter location

    Ditto every comment..........but call for a complete system evaluation because if an installer was this stupid, who knows what else is wrong.


  7. #7
    Join Date
    Dec 2009
    Location
    Florida
    Posts
    552

    Default Re: HVAC Filter location

    Quote Originally Posted by Lon Henderson View Post
    Ditto every comment..........but call for a complete system evaluation because if an installer was this stupid, who knows what else is wrong.
    Ya mean like the gas line?


  8. #8
    Join Date
    Mar 2007
    Location
    Lake Barrington, IL
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    1,363

    Default Re: HVAC Filter location

    Seriously, this could be an easy miss if your attention was diverted or you were rushing.

    Eric Barker, ACI
    Lake Barrington, IL

  9. #9
    Join Date
    Mar 2007
    Location
    Ormond Beach, Florida
    Posts
    26,243

    Default Re: HVAC Filter location

    Quote Originally Posted by Rich Goeken View Post
    Ya mean like the gas line?
    and the vent

    and the NM cable

    and ...

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  10. #10
    Bert de Haan's Avatar
    Bert de Haan Guest

    Default Re: HVAC Filter location

    I understand why the location is incorrect as far as the filter not catching dirt before it gets to the furnace but I do not understand why it should affect the load on the fan. Is there much difference between a fan sucking air through a dirty filter as opposed to pushing it through a dirty filter?


  11. #11
    Join Date
    Mar 2007
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    Ormond Beach, Florida
    Posts
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    Default Re: HVAC Filter location

    Quote Originally Posted by Bert de Haan View Post
    I understand why the location is incorrect as far as the filter not catching dirt before it gets to the furnace but I do not understand why it should affect the load on the fan. Is there much difference between a fan sucking air through a dirty filter as opposed to pushing it through a dirty filter?
    Bert,

    With the filter before the fan, the interior of the AHU stays clean ... er ... 'cleanER' , including the blower blades.

    With the filter after the fan, the blower blades will be impacted with all that dirt and dust before it gets to the filter, and this will build-up rather quickly on the blower blades when there is no filter in front of it. That dramatically reduces the efficiency of the blower and adds a heavy load to the blower.

    That dirty blower reduces its ability to move air and thus reduces the cfm the unit is capable of moving.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  12. #12
    Bert de Haan's Avatar
    Bert de Haan Guest

    Default Re: HVAC Filter location

    Ah. Thanks.


  13. #13
    Join Date
    Mar 2007
    Location
    Plano, Texas
    Posts
    4,170

    Default Re: HVAC Filter location

    Quote Originally Posted by Bert de Haan View Post
    I understand why the location is incorrect as far as the filter not catching dirt before it gets to the furnace but I do not understand why it should affect the load on the fan. Is there much difference between a fan sucking air through a dirty filter as opposed to pushing it through a dirty filter?
    Big difference when talking about a squirrel cage blower as opposed to a propeller type fan. Reducing the amount of air on the suction side will reduce the load on the fan much like on a centrifugal water pump. play with a blower and an amp meter when you get the chance, it can be an eye opener. It is kind of counter intuitive unless you under stand the physics behind air flow and centrifugal blowers.

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

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