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Mold on Santa Fe dehumidifier filter

user-5946022 | Posted in General Questions on

My sealed/encapsulated crawl space has a ducted Santa Fe whole house dehumidifier with filter.

Ultra70 Dehumidifier

Today I changed the OEM Santa Fe filter, and was shocked to discover the outgoing side next to the fins is covered in mold.  Suprisingly, the mold is on the upper 3/4 of the filter  (so it is not water dripping down fins pooling at the bottom and wicking up).

I checked the pan and drain, both are free of clogs, so its not water backing up.

The unit is independently ducted both sides (supply and return) and nothing is obstructing the airflow on either side.

What would cause the filter to mold like this???

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Replies

  1. walta100 | | #1

    Mold will grow anyplace you give it 3 things.
    Warmth anyplace over 45°
    Moisture anyplace over 50%
    Food almost any cellulose or starch.

    Is there any chance the filter got so dirty that it restricted the air flow and got pulled into contact with the damp coil?

    Walta

  2. user-5946022 | | #2

    The filter is really not that dirty - if it were not for the mold, I may have considered leaving it in there for awhile longer.

    But your restricted air flow comment got me thinking - the supply and return collars are 8" round, and it calls for 8" ducts (50 sq inch area)
    On my install, from the dehumidifier return, that 8" round duct transitions
    - to a short section of 6" round duct (28 sq inch area)
    - to a boot that transitions to a rectangular 3.5 x 12 duct (42 sq inch area)
    - to a 12 x 12 grill (which is rated as a 98 sq inch free area)
    I am wondering if it is possible the 6" duct constricts the airflow causing the fan to pull the filter to the damp fins? Seems unlikely but...

  3. Expert Member
    DCcontrarian | | #3

    Is it possible that the filter is just close enough to the cold fins that its surface drops below the dew point and it gets condensation on it at times?

    1. charlie_sullivan | | #4

      That sounds likely. A possible solution would be a filter box a foot or more upstream of the dehumidifier. It's also possible that running a lower humidity setpoint would help. Possibly also insulating the supply duct, to keep the air warmer as it heads toward the cold dehumidifier, at the expense of some efficiency.

      Maybe the best solution is a filter at the intake duct termination in the conditioned space--that could be easier access for filter replacement as well as avoiding the problem you describe.

      1. user-5946022 | | #6

        @charlie_sullivan: You wrote "Possibly also insulating the supply duct, to keep the air warmer as it heads toward the cold dehumidifier, at the expense of some efficiency."
        Did you mean insulating the return ducts (which are supplying air to the dehumidifier)? If so, that duct is insulated. If no, can you please explain?

        Regarding a filter at the intake termination, I have a filter grill at the "start" of the return in the conditioned space, and it is indeed MUCH easier access for replacement. I removed the filter from the filter grill and used the OEM in the unit due to concerns about potential restriction in the return system.

  4. walta100 | | #5

    Any chance the filter happened to get installs backward. It would have supports of the low-pressure side.

    I don’t like the restricted ductwork. The reduced air flow will lower the temp of the coil. Could the coil get the filter cold enough to condense water? Maybe but it sounds unlikely.

    Walta

  5. user-5946022 | | #7

    @walta100: I can confirm filter was installed in the correct direction (not backwards).

    Also, can you please help me understand the "restricted" ductwork a bit more. Since I used the OEM filter inside the unit, rather than a filter at the filter grill, wouldn't the air going through the very short 6" diameter section just move faster as it goes through there? Or is that 6" section restricting all air beyond what can get through 28 square inches at whatever cfm the fan in the dehumidifier pulls air?

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