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  1. #1
    Join Date
    Sep 2017
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    A/C output is very humid

    Our house recently has had a normal humidity level that averages about 65%. We have had several folks come out to diagnose, but the best response we got was to seal the seams around our vents so that crawl space air doesn't seep into the house. We did an experiment by placing a humidity gauge on the floor vent while the A/C was running. The gauge went through the roof, measuring as much as 84% humidity. This tells me it's not the vents, but the air conditioner itself. Any thoughts on what could be causing this?

  2. #2
    Join Date
    Apr 2017
    Houston, Tx
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    the cool air coming from your evaporator is supposed to be nearly 100% RH.

    keep in mind that RH is a function of temperature and actual humidity( absolute humidity = grains of water per cubic foot of air).

    when your evap is cooling the air it cannot condense anything below the temperature of the evaporator... so the air just becomes saturated. this is a good thing though because once the saturated and cold air warms to your room temperature the RH of that air will drop alot.

    im not saying you have 0 problems... probably the contrary honestly, but taking the air stream humidity is not a good way to find out whats going on with your humidity.

  3. Likes kdean1, WAYNE3298 liked this post
  4. #3
    Join Date
    Nov 2006
    Athens, Ohio
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    ^^ x2
    AOP Rules: Rules For Equipment Owners.

    Free online load calculator:

    There = not here. Their = possessive pronoun. They're = they are
    It's = contraction of it is. Its = the possessive form of it
    Too = also. To = expressing motion. Two = 2
    Then = after that, next. Than = indicates a comparison.
    Questions should end with a question mark "?" Statements end with a period "."

  5. #4
    Join Date
    Feb 2016
    Louisburg Kansas
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    152 is correct. Air is delivered at roughly 100% RH but if heated sensibly to say 72F dry bulb the measured RH will drop considerably. It depends on the air delivery temperature, how much the air is heated and how it's heated. Like 152 I'm not saying there is no problem but you haven't identified one.

  6. #5
    Join Date
    Aug 2002
    Southold, NY
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    RH is measured at the return not supply.

  7. Likes queequeg152 liked this post
  8. #6
    Join Date
    Jun 2003
    Madison, WI/Cape Coral, FL
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    A small science project. Measure the temp/%RH in the room. Then take a plastic bag with the meter in the bag, collect the air from your cold supply. Seal the bag full of cold wet air and allow the bag to warm to room temperature. If your a/c removing moisture, the meter will show lower %RH than the room air.
    Also by calculating the dew point of the room air and by comparing it to the a/c supply air dew point to determine decrease or increase in the a/c supply air.
    A correctly setup a/c will reduce the dew point by 6-8^F, supply verses room air.
    This will keep you home <50%RH during typical hot day cooling.
    When the sun goes down or on a cool wet day, the a/c is not running enough to remove the 4-8 Lbs of water per hour needed to maintain 50%RH. The simplest solution adding a small whole house dehumidifier like the Ultra-Aire, a site sponsor.
    Crawlspaces are another can of worms. Ideally they should have a vapor barrier on the earth and outside vents should be closed when the outdoor dew points above what you want in the home. This is typically <50^F dew point.
    Hope this helps. You a/c can be adjusted to get you to <50%RH during peak cooling loads. Adding the a small whole house dehumidifier could keep you home and crawlspace <50%RH throughout all seasons. More comfort and healthier.
    Keep us posted.
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  9. #7
    Join Date
    Jan 2004
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    Check the temp and RH entering the return, and then leaving the supply, and tell us what those readings were.
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