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  1. #1
    Join Date
    May 2015
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    1" Prefilter for a 4" Media filter?

    I will have a 4" media filter installed with my new FAU. I also plan on installing a static pressure measuring device (like amazon.com/gp/product/B009PAN3C8/ref=ox_sc_act_title_2?ie=UTF8&psc=1&smid=ATVPDKIKX 0DER) to determine when the filter should be replaced.

    1) How much static pressure can a new variable speed fan overcome without damage so I can determine the maximum filtration (MERV 8, 11, 13, 16) I can use?

    2) Can/Should I have a cheaper 1" pre-filter (MERV 4) installed to catch the larger particles allowing the more expensive media filter to last longer by not filling up with larger particles and thus keep the static pressure lower? Replace the 1" every 1-2 months allowing the 4" to last 12+ months.

    3) Can/Should I also add a charcoal filter as well for odor and VOC control? Should the charcoal filter be after (between the pre and media filter) or before the pre-filter? That would be 3 filters in a filter rack.

    4) At what static pressure should one replace the filter?

  2. #2
    Join Date
    Aug 2013
    Location
    Visalia California 93291
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    What is the capacity of the unit and how many filters? I am a believer in multiple returns and multiple filters- 1 at the furnace IMHO is not a great idea

    So I just read your other post and at that capacity 1 filter would be OK.....anything over 2 we go multiple-- see attached chart
    Attached Images Attached Images
    Last edited by lkapigian; 05-07-2015 at 04:23 PM. Reason: Read Other Post

  3. #3
    Join Date
    May 2015
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    19
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    Thread Starter
    I was thinking a filter rack under an upflow FAU. The filter rack could have multiple filters (pre, charcoal, media) in a series. See picture.

  4. #4
    Join Date
    Aug 2013
    Location
    Visalia California 93291
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    what is the rating of the charcoal and is there an odor issue in the home for VOC you really should ventilate

  5. #5
    Join Date
    May 2015
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    Thread Starter
    Like many filters they don't give the static pressure drop and/or the MERV rating. I was looking at something like 16x25x1 or 2" if I can find it (amazon.com/16x25x1-Accumulair-Carbon-1-Inch-Filter/dp/B0009GVXDS).

    Found a carbon filter that is .5" new to 1" dirty at 250 fpm (grainger.com/product/AIR-HANDLER-Activated-Carbon-Air-Filter-6W743). That seams like a high wc at a low fpm. Does not say the MERV rating.

    This carbon/MERV-6 filter does not give wc (airfilterusa.com/astro-sorb-activated-carbon-expanded-metal-pleated-16x25x2.html).

    When the condo is closed up it just smells musty. We open windows during good weather. It looks like fresh air intake is not possible without opening up walls, ceilings, stucco, HOA approval, etc. So filtration and charcoal is next best option. VOCs from new carpet, candles, cooking, car fumes, etc.

    Just trying to figure out a good combination of filters that keeps the static pressure drop low. I have the height for a filter rack but max out with a 16x25. Especially because the FAU bottom opening is only 14x24 ish.

  6. #6
    Join Date
    Aug 2013
    Location
    Visalia California 93291
    Posts
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    ditch the carbon , you will kill your air....5 @250...your unit total is rated at .5

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