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Who knows home HVAC filters?

Discussion in 'Fred's House of Pancakes' started by egg_salad, May 6, 2019.

  1. egg_salad

    egg_salad Active Member

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    Folks around here seem to have all manner of useful knowledge, so let's give this one a shot...

    Once again, I've moved into a residence with an obscure HVAC filter size. The lady at Ace Hardware looked at me like I had two heads when I asked her for a 14x18x1.

    This being the age of the Internet, of course I can order any dang size online. That's certainly a viable possibility. But while poking about online, I've come across washable filters - the K&N of the HVAC world :)

    I did some research, and there do seem to be some downsides - they don't filter very fine particles, and they have to be absolutely dry before reinstalling (which might lead to a few hours system downtime while one waits for it to dry). I can probably cope with both of those.

    Are there any HVAC professionals around here that can address this - or perhaps homeowners who have experience with them?

    Thanks
     
  2. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    I’m not an HVAC professional, but I’ll offer 2 bits of advice.
    TIFWIW.....

    1. Engineering is like politics usta be, a give and take process.
    K$N filters are engineered to provide maximum air flow at an acceptable level of filtration, and unless the user is very VERY careful oil contamination of the intake is a common result.
    More dirt getting into the engine is ALWAYS the result.
    Think carefully before you apply this to the world of HVAC.

    B. You may be able to change your HVAC filter size more easily than you think, especially if it’s in a closet.
    I faced a problem where the filter size in my HVAC closet was not resized when the previous owner installed a larger heat pump....inconveniently, right before I bought the house.
    Since my closet has 2 exposed walls, adding another filter for $300 in parts and labor was one of the solutions.
     
  3. ChapmanF

    ChapmanF Senior Member

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    Also, a thing I ran into when doing some HVAC upgrades:

    Old low-efficiency furnaces would blow relatively hot air at lowish flow rates. New higher-efficiency sources depend on higher airflow to deliver the same amount of heat at lower temperatures of the delivered air. That can require re-figuring the adequacy of the ductwork.

    The adequacy can be confirmed by measuring the external static pressure drop when the system is operating (at its highest output). There will be a maximum allowable figure in the literature for the system. The ESP drop includes all of the ductwork and the filter. Different filters can have quite different pressure drops at the same airflow.

    Back when I was trying to get that information, I found only 3M to be easy to get it from. Even they did not print the info on their retail packages, but it was easy to contact someone at the company who was knowledgeable and provided the specs. At other outfits, it was more like talking to a first-tier CSR who would say "you want to know what?".
     
  4. sam spade 2

    sam spade 2 Senior Member

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    If you are concerned about good air filtration, you will NOT use washable filters.
    In your car OR your house.
     
  5. TMR-JWAP

    TMR-JWAP Senior Member

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    Keep in mind this one very important item......HVAC filters are in the system to keep the air handler coils clean and relatively dust free, not to solve everyone's allergies. This is performed more than adequately by using the inexpensive blue/white fiber filters. Installing the expensive "catch everything under the sun" filters can be detrimental to the life of your HVAC equipment, as those filters can significantly impede airflow. There should be 350-400 cfm per ton of HVAC capacity. That can be calculated by static pressure readings. If you need additional filtration for personal health issues, there are filter systems designed for that, which can be installed.

    If you would like professional opinions, please go here and ask away....

    HVAC-Talk: Heating, Air & Refrigeration Discussion
     
    Prius Maximus likes this.
  6. egg_salad

    egg_salad Active Member

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    Thanks for the advice. That forum TMR pointed out told me everything I needed to know to make the choice to stick with disposable filters and now I know which direction to head.
     
  7. Mendel Leisk

    Mendel Leisk Senior Member

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    I put filters on all the return air inlets. This was after cleaning the hot and return air circuits, doing tape/mastic on the hot air circuit, and foil tape and caulking of the return air circuit. Now I pretty much only need to clean or replace the air inlet filters, and the filter at the furnace stays pretty much pristine. Luckily most of the system is accessible, in the crawl space.

    I found a lot of crud in both circuits, even construction debris in one or two pipes (sawed of bits of 2x4 just dumped down the vent...). There was a complete fail of one branch of the return air circuit: return air grill in the wall just "venting" into the crawl space, due to an oversight, not closing in space between studs. Also some really bad gaps in the return air circuit, and questionable practice, using the space between joists, having electrical wiring run through the "seal", failed seams, and on and on.