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Thread: 2 filters on air handler?

  1. #1
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    2 filters on air handler?

    So I have 2 returns servicing 1st fl and basement room(a small bedroom). Return on1st fl is in floor and collects alot more dust then all my other returns in ceiling and wall. I was thinking of installing 1 inch MERV 7 pre filter there on top of existing 4 inch MERV 11 at the unit. Do you think it can hurt the motor?

  2. #2
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    It could only hurt the blower motor if it's an ECM or variable speed, since those kind will sense the drop in airflow and will work harder to try to overcome it. A normal old-school PSC (or 3 phase) motor would actually like the reduction in airflow to a certain extent, since that means it would have less work to do (less amp draw).

    The main thing to look out for is too much temperature rise in heating mode if it has electric or gas heat, too high of head pressure if it is a heat pump, and too low of suction pressure if it has cooling. As long as you have the tools and abilities to check those things after you do your little experiment, then I say sure, give it a try.
    If at First You Don't Succeed, Skydiving Is Not for You.

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  4. #3
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    Don’t forget low suction pressure in cooling mode, higher pressure ratio, reduced efficiency, and possible iced over evaporator coil.
    Must verify airflow/static pressures.

    Why not just change the filter as needed?

  5. #4
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    Thread Starter
    Motor is PSC and I have 2 12x12 returns on it. Yeah changing filter more often is fine too. I don't know, just had that thought of prefilter due to return location. I always see so much crap on the floor. I am not hvac installer so I obviously don't have tools to check anything....

  6. #5
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    Quote Originally Posted by kolyan View Post
    Motor is PSC. Yeah changing filter more often is fine too. I don't know, just had that thought of prefilter due to return location. I always see so much crap on the floor. I am not hvac installer so I obviously don't have tools to check anything....
    Central vac?

  7. #6
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    Thread Starter
    Quote Originally Posted by ehsx View Post
    Central vac?
    Yes

  8. #7
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    A prefilter is likely not gonna hurt anything so long as the main filter is not neglected. Best quick check a person can make is what happens to the delta T.. If your air temps change significantly after adding the pre-filter than its a bad idea. Remember the system was designed to have to media filter only. Adding the extra filter can become as detrimental to the entire system as never having any maintenance at all. I see it all the time where an attempt is made to improve one portion of the system while compromising all the rest of the system. Best advice I can offer is to have a good tech who cares check all sides and help you determine the solution.

  9. #8
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    In addition to the above, if you are only going to stick the filter in the one return then you may alter the balance of the system and find that you get hot spots and cold spots in areas that they may not have been before. I agree with the above, best to have some experienced eyes in this to run the tests and monitor the system performance so it is sure to function properly after the change.
    Quickly, I must hurry, for there go my people and I am their leader!

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