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  1. #1
    Join Date
    Apr 2012
    Location
    Northern Virginia
    Posts
    143

    Default Central A/C Filters - Air Flow

    I noticed that my new air filters (my size is 20 x 20) are rated at MERV 13 and the register air flow at the 2nd floor seems reduced. I wonder if I should actually go to a "cheapo" filter because my A/C runs continuously during hot days (No. Virginia - June to mid-Sept) at a setting of 76 or lower (resulting in 82 on the 2nd floor).

    A less restricted filter would allow more conditioned air to the 2nd floor, is my thinking.

    Like many 1-zone A/C 2 story houses, during hot & hotter days (like now) the 2nd floor can be 6-10 degrees warmer than the 1st floor. My house is 1.5 story, "cape cod" type with the 2nd floor basically in the attic. Also, the main 1st floor is in brick which I think helps keep cooler while the 2nd flook is clad by the shingle roof and 1964 insulation and soffit attic venting.

    I tried to re-balance by reducing the 1st floor air register flow, thinking more air would be "forced" to the 2nd floor. The 2nd floor is 50% the size of the main 1st floor, and thus, the 4 air registers in the 2nd floor are fighting a lot of heat from being in the attic.

    Any thoughts.

  2. #2
    Join Date
    Aug 2007
    Location
    Maryland
    Posts
    1,580

    Default Re: Central A/C Filters - Air Flow

    Merv 13 filters will reduce the air flow. While they will trap smaller particles, they also may cause a problem if the air handler isn't designed for it. I would go back to the less expensive/less restricive filter.
    Rebalancing is a good idea, but there is only so much you can do. Can the fan speed be increased

  3. #3
    Join Date
    Jul 2009
    Location
    Northeast
    Posts
    661

    Default Re: Central A/C Filters - Air Flow

    Yep, use the cheapo's for sure, if there was plenty of airflow before and it didn't need rebalancing. The Merv 13's are good if you have alergies.

  4. #4
    Join Date
    Jul 2012
    Location
    Manhattan
    Posts
    17

    Default Re: Central A/C Filters - Air Flow

    Well, which ever way the air is going, and look at side of filter it will have arrow with the direction of air flow!!

  5. #5
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,731

    Default Re: Central A/C Filters - Air Flow

    If you are feeding the air to the filter in a remote location from the furnace, then you might be able to have a larger filter box put it so that you can use a 20x25 or 20x30. Note: 20x30 filters are not carried everywhere. This is if you feel the need for the better filters, i.e. dust infiltration problems or allergies.

    Another possibility might be a booster motor in the riser duct to increase air flow to the second floor. This won't work if all the ductwork for both floors is in the space between the first and second floors, that is vents in the ceiling of the first floor and in the floors of the second floor.

    Increasingly expensive solutions include window air units on the second floor, a separate HVAC system located in the attic for the second floor, mini split systems for the second floor and an insulation update on the second floor.

    One last thing is to look at the MERV 13 filter itself. Filters come in varying qualities. You might find a MERV filter that has more pleats and or deeper pleats that offers the same MERV filtering but with a higher flow rate, higher cost though, but would last longer.

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