HVAC dehumidifier

Discussion in 'HVAC' started by scottc1, Sep 2, 2018.

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  1. Sep 2, 2018 #1




    New Member

    Sep 2, 2018
    Likes Received:
    Hello. I have a pretty decent HVAC system for my house (2330 sqft.) And there has never been any issues cooling the house at night. I live in Florida and just purchased a small dehumidifier to help with the high humidity levels I consistently get each day. The highest levels I get are around 60% and when house cools to 70° at night, the humidity drops to mid 40%.

    I'm wondering if anyone can help me figure out a way to keep humidity levels below 50% throughout the day.

    Combination of using ceiling fans and dehumidifier?

    Placing dehumidifier in front of HVAC intake vent and running fan feature on HVAC?

    Any advice would help.
  2. Sep 20, 2018 #2




    Active Member

    Nov 12, 2016
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    hi Scott,
    Since the AC unit is essentially a large dehumidifier, its ability to dehumidify can be improved.
    1. make sure the cooling coil (A-coil or evaporator) is CLEAN. A coating of molds, dirt, etc on the surfaces will reduce the dehumidification.
    2. have a technician reduce the air handler's blower speed. This takes some experimentation, because a too-low blower speed will let the cooling coil freeze up at times, and/or may not let the machine cool the space well.
    3. make sure the blower stops when actual cooling stops. Do this by setting the thermostat FAN switch to AUTO. If the blower runs when no cooling is happening, water in the A-coil will re-evaporate into the house.
    4. keep outdoor humidity out of the house. Doing this could be many small tasks ... seal up cracks/openings in the ceiling, walls, floors, windows .. to keep outside air out of the house. Avoid running powerful exhaust fans (kitchen, bathroom, clothes dryer) when the humidity is high outside.
    5. use a high-efficiency air filter in your air handler. This helps keep the A-coil clean. I recommend one of the 3M Filtrete filters, rated MERV 12 or higher. These filters flow air well, and last several months.
    6. use the bathroom exhaust fan during showering, and for awhile afterward. Using a timer type of wall switch helps you do this.
    7. make sure your kitchen exhaust fan actually vents to the outdoors, and use it when cooking things that generate steam.
    8. if your home is on a crawlspace, install a vapor barrier under the floor joists, to keep moisture out of the living space. Also, make sure the crawlspace has air vents, and that those vents actually let air through.
    9. if your walls and ceiling don't have a vapor barrier, a good quality of impermeable paint will help a lot.
    10. use the HVAC indoor air handler to maintain a slightly positive pressure inside the house. This can be done by adding a small duct between the return side of the air handler (before the filter), to the outdoors. This allows the air handler to draw in a small amount of outdoor air, which greatly reduces outdoor air from entering through cracks and openings in random places. Be sure to use a bug screen on the outdoor end of the duct.

    One final thought on this .. if your HVAC system capacity is too high for the size of the house, the AC will not run long enough to dehumidify the indoor air well, and the indoor space will feel a little like a "cave" .. cool and damp. There are modifications a technician can do to reduce the unit's capacity ... somewhat. But this is not something a homeowner can do himself.

    best regards,
    retired KY HVAC Master Contractor

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