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  1. #1
    Join Date
    Aug 2008
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    Thiinking of upgrading to 4" filter grilles instead of 1". Question for pros

    The consensus on the max MERV 1" filter from most pros is a MERV 8. I''ve followed this religiously w/my filter purchases for my Amana ASZ 18 HP.

    Now, I'm considering moving up the filter grilles or grille filters (?) of the 4-5" thickness.

    Question: b/c its NOT a 1" filter, can I increase the MERV rating from 8 to more, while maintaining just as good or better air flow?

    In other words can would a MERV 8=MERV 12 in a 4 or 5 inch.

  2. #2
    Join Date
    Aug 2003
    Fort Worth, TX
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    Pressure drop is the all-important factor here. A 4" MERV 8 will have much less pressure drop than a 1" MERV 8, due to much more surface area for dust entrapment.

    That said, if you go crazy higher on the MERV ratings at 4", you could be at or above the pressure drop you're now seeing with the MERV 8 at 1".

    High MERV filters at an air handler are thought as an ultimate solution for controlling dust in a house. They are not. Most of the dirt you want to control precipitates out of the air long before it can get to the filter. So all a higher MERV filter does is, yes, protect the equipment surfaces better, but gone overboard actually harms system performance, and can lead to heat exchanger (gas furnace) or compressor failure (heat pump or straight a/c).
    Building Physics Rule #1: Hot flows to cold.

    Building Physics Rule #2:
    Higher air pressure moves toward lower air pressure

    Building Physics Rule #3:
    Higher moisture concentration moves toward lower moisture concentration.

  3. #3
    Join Date
    Oct 2010
    Anderson, South Carolina, United States
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    Without checking ESP you will not know if any filter will harm any system. Yes you can get better merv ratings with 4 or 5 inch filters over a 1 inch. Your ductwork leaks are a large contributor to dust in a home. In a completely sealed duct system there should never be any dust in the system, filter should catch it all. Negative pressure homes, which most are due to dominant supply leakage, will pull in insulation, dust, and dirty air from thermal envelope leaks from attic and crawl space. This is usually the cause of a "dusty" house.

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