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  1. #1
    Join Date
    Feb 2006
    Posts
    212
    This is my setup...

    I was using a filtrete filter and recently stopped buying them because of their restictive nature. I have also recently installed a bypass HEPA filter on my system. I now use the cheap blue filters at my return duct. I was told that is OK but I really am having a hard time with this decision. The HEPA only goes through 10% of the air from the return and the blue filters are the only thing between the components and the dirt.

    I've been changing the the previous Filtrete filters religiously for 5 years and will do the same with the new filters. I'd hate to get my components dirty at this point. thanks.

    My ESP was tested and is within reason. I would like to step up to a Merv 4 or 6? if possible. As long as it's better than the blue ones. Can anyone make a recommendation for a brand with the lowest restriction?


  2. #2
    Join Date
    Oct 2004
    Posts
    167
    You using a filter grill? If so, maybe adding additional returns, each with a filter grill would keep the pressure low.

    If youre at the air handler with your filter, then you'd need to know the cfm of the unit and the size of the filter for a recommendation. (or go with multiple filter grills or have a 4" filter housing installed at the furnace - which sometimes isnt that hard.)

  3. #3
    Join Date
    May 2002
    Location
    Colorado
    Posts
    697

  4. #4
    Join Date
    Feb 2006
    Posts
    212
    I recently added a second return with a filter grill on it to the system. Now I have one 14" X 30" return with grill(1") and one 8"X 30" return with grill.

    I have the blue filters on each of these grills now. That Grainger filter looks good. Is it a "better" filter than the cheap blue ones? Likre I said, I'm having a hard time believing those transparent blue filters will work that great, but I STILL don't want to ever go back to the MERV 1Billion of the Filtrete filters. I may need somewhere near the lower end of Merv rating. Thanks for the site.

    Do the Grainger filters have a Merv rating? or a rating that it can get compared to?

  5. #5
    Join Date
    Oct 2004
    Posts
    167
    Only bad thing is that the 8x30 is a very odd size for a manufactured filter.

  6. #6
    Join Date
    Feb 2006
    Posts
    212
    ^^Yes, but they seem to make them any size that one may need. Given the many choices... Merv 4...6 ...8...? I just want to purchase the filter that would definately keep my unit clean with a sensible restriction.

    The Grainger link has the 8X30 as one of their sizes.

  7. #7
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    Post Better to measure than guess, but...

    The way to be sure is to have your system's ESP tested with those pleated filters installed -- but few people will actually do that and I don't really expect you to.

    I have had the advantage of a few tests in 2004 using different filters in my own system, using a Dwyer red-oil type manometer. At that time I was measuring only vacuum in the return plenum, I propose we can reasonably assume the other component of ESP will remain constant.

    This would be most useful if I had tested that infamous 3M Filtrete filter but I did not. The closest tested were "Arm & Hammer" 8 and 10 MERV filters, as well as those blue mesh transparent "rock stopper" ones. There was one 600 sqin filter, for 171 sqin per ton of AC airflow -- generally considered adequate but not generous.

    Results:
    1) 10 MERV A&H pleated: .190 inch w.c. vacuum
    2) 8 MERV A&H pleated: .165
    3) Blue mesh rock stopper: .060
    4) No filter at all: .020

    You can see the most restrictive filter increased vacuum by .13 over the blue mesh type. These were new filters, word on this board is the 3M Filtrete loads up and becomes more restrictive sometimes in the first 2-4 weeks of service. After some return improvements my system has lots of filter area and I am using those 8 MERV A&H brand, no loadup is apparent under these conditions, and after 12 months of service ESP has not risen significantly.

    The above measurements cannot be guaranteed to apply to your system, they were on my system as of September 2004 before returns were added. I would guess your numbers would be comparable, but of course be wary it is *your* system at risk if you guess too much.

    After adding sizable return capacity which nearly doubled filter area to 330 sqin/ton, I find the 8 MERV filters increase ESP .03-04 inch w.c., and the 10 MERV by .04-05, both compared to the blue mesh type. It matters much less if you have truly generous filter area. The lesson here is that systems with skimpy filter area and already high ESP, are the ones particularly at risk from using restrictive filters.

    One other attractive option which is safe for anybody, would be to apply spray-can of filter "enhancer" to a mesh type filter. I have "Air-Kontrol FILTER PLUS" brand which I bought at Home Depot, my AC tech approves of this. Of course you may want to spray the filters rather more often than you change them, and in the process watch how quickly they get dirty. However my AC tech says that the filter does not have to be changed simply due to being dirty. Rather, it filters better until there is so much dirt that it begins to obstruct air flow.

    Hope this helps -- Pstu

    [Edited by pstu on 05-24-2006 at 08:05 PM]

  8. #8
    Join Date
    Feb 2006
    Posts
    212
    Thanks pstu, great stuff!

    I've actually had my static pressure tested but don't have the numbers handy. They weren't the best numbers but I think they were just on the borderline of where they should be. I had a before and after test done when rerouting and sealing my ducts and adding return air to the system. It was part of the HER/SER test by an NCI pro. The original static pressure test was done WITH the Filtrete filter, but the second test was done with the blue, cheap filter (and a bunch of other changes as noted).

    Anyway, I was concerned about the blue filters and wanted a very slight bump up to protect the equipment but of course don't want to bump too much and hurt it as well.

    I may look for those numbers and decide from them.


  9. #9
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    It happens my system also had an airflow test by an NCI trained (very freshly trained) tech, and I had bought the restrictive filters thinking that more expensive means better. When I saw the substantial bowing of the filter in its frame, it became obvious to me that the filter was part of the low-airflow problem.

    That was on the *other* system in my house, which at the time had .45 inch w.c. measured vacuum, and estimated 0.70 inch ESP before improvements. That one was the problem system, the tech measured only 723 CFM airflow on a 3-ton system, but I now believe that was partly an error in measurement. A later tech "discovered" the high fan setting and measured 1110 CFM, you can perhaps sympathize with why I am skeptical sometimes.

    Being unable to solve that problem led me to change techs several times, but now I have much larger return capacity, 450 sqin/ton filter area, a VS blower and ESP in the .45-55 range. Much more robust now.

    Best wishes -- Pstu

  10. #10
    There's also a Practical Pleat, .093 Pressure Drop on 5" - only good for Return Air Grille. www.filterfolks.com

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