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  1. #1
    Join Date
    Jun 2017
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    1 inch to 4 Inch Filter Conversion

    I have a two zone central AC system with three ceiling return intakes with 1 inch thick filters (one for the first floor and two for the second floor). I'd like to retrofit the returns to accommodate 4 inch filters since my wife has allergies and the 1 inch filters can't filter out the allergens without unacceptable air flow restrictions.

    Looking at the filter frame, it seems like an easy job to replace the 1 inch frames with 4 inch frames. There is sufficient clearance and I'd like to do the job myself. Despite my best attempts, I didn't get anywhere when searching online for return filter housing/box, etc. I see a lot of filter grilles but can't seem to find the boxes.

    I would appreciate some help with the right term for what I'm looking for and some places that sell these frames. I need a 12x12, 12x24 and 24x24.

    Thanks for your help.

  2. #2
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    27,164
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    Quote Originally Posted by c210flyer View Post
    I have a two zone central AC system with three ceiling return intakes with 1 inch thick filters (one for the first floor and two for the second floor). I'd like to retrofit the returns to accommodate 4 inch filters since my wife has allergies and the 1 inch filters can't filter out the allergens without unacceptable air flow restrictions.

    Looking at the filter frame, it seems like an easy job to replace the 1 inch frames with 4 inch frames. There is sufficient clearance and I'd like to do the job myself. Despite my best attempts, I didn't get anywhere when searching online for return filter housing/box, etc. I see a lot of filter grilles but can't seem to find the boxes.

    I would appreciate some help with the right term for what I'm looking for and some places that sell these frames. I need a 12x12, 12x24 and 24x24.

    Thanks for your help.
    You'll need a contractor on site to take static pressure readings too see if the equipment can handle the extra resistance of pleated filters and make the modifications to the duct work!

  3. #3
    Join Date
    Jun 2017
    Posts
    3
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    Thread Starter
    Thanks for the prompt response Pecmsg. But I'm a bit confused. I thought that a larger filter surface area would allow for better airflow for a longer period of time. I am using 1 inch pleated filters now but I have to change them very frequently.

    I understand that the static pressure would be restricted if I go with a higher MERV rating filter but would that be the case if I change from 1 inch to 4 inch all other things being equal?

  4. #4
    Join Date
    Jan 2004
    Location
    PA
    Posts
    78,507
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    Honeywell makes 4" filters that fit into 1" frames.

    FC40R1094 12x12x4
    FC40R1037 12x24x4
    FC40R1078 24x24x4

    These would be MERV 10. You may need to have an additional return added to your system, depending on how well your returns were or were not sized.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

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