Stick with fiberglass furnace filters?

Discussion in 'HVAC Heating & Cooling' started by AlGreen, Jun 23, 2020.

  1. AlGreen

    AlGreen Member

    Joined:
    Jul 25, 2016
    Location:
    New Jersey
    We've lived in our current house for about six years. It's a two zone set-up with Lennox furnaces and Carrier central air units (the Carriers were bought by us three years ago). I've been using fiberglass filters the whole time, mostly because of concerns about higher MERV pleated filters causing pressure drop issues. Short of having an HVAC tech come out to run calculations on our system, am I correct that there's no way to know if it can handle anything more than the fiberglass filters?
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    What does the operator's manual say? I'd also call the manufacturer to see what they recommend.

    Most fiberglass filters don't block much more than the biggest particles which can let your heat exchanger and evaporator coils get dirty. If those get cleaned periodically, that may not be an issue. Pleated paper filters come in all sorts of various MERV ratings.
     
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  4. AlGreen

    AlGreen Member

    Joined:
    Jul 25, 2016
    Location:
    New Jersey
    Thanks. The manual for the Lennox furnace recommends using a washable foam filter.

    https://www.lennoxpros.com/p-8-7822-filter-air/p/30335

    Re pleated filters with lower MERV ratings, unfortunately that doesn't necessarily mean that they also have an acceptably low pressure drop.
     
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  5. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
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    That's right- the correlation between MERV rating and pressure drop isn't obvious or simple. The MERV rating can be tested at any of a handful of air flow velocities, which may or may not be relevant to your system. With a $100 dual port manometer you could take the guesswork out of it and MEASURE the static drop of different filter media, but that's more than most homeowners would ever do.

    Cutting in an oversized 4-6" deep pleated filter would ensure the pressure drops are pretty low no matter what cfm or air velocity you're running, and they need not be changed very often at all. (I try to remember to do it once per year, but I've managed to forget for several months at a time, and have started tagging the door to the AprilAire 2400 with the date when installing new filter media.)
     
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