Humidity Control - Oversized A/C?
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  1. #1
    Join Date
    Jun 2005
    Posts
    1
    I've got an 8 year old Comfortmaker AG042GB 42,000 BTU with a 10.4-11.5 SEER rating. The evaporator is U42PC22A1 with an 078 restrictor according to the label. The furnace is a Comfortmaker GUK100N16C1.

    I've always had to keep the house quite cool (72 or lower) in order to keep the humidity below 60%. My suspicion is that the A/C is oversized. The house is a 2000 square foot two story and well insulated (R50 attic, R15 walls, triple pane low-e Pella windows). The house is also well shaded. Additionally the house is about 1/2 mile inland of Lake Michigan wich reduces outside temperatures 6-8 degrees vs. the surrounding area but doesn't reduce the humidity.

    The air conditioning normally runs about 5 minutes per cycle.

    I realize that accurate sizing requires detailed calculations beyond what can be done here.

    Mainly what I'm trying to do is to become a bit more knowledgeable before I start talking with contractors. After reading this forum for a while I've seen a few options other than replacing the air conditioner with a smaller unit:

    Don't use the continuous fan setting
    Slow the blower down
    Replace the restrictor with a TXV and slow the blower more
    Get a high capacity dehumidifier

    I already have a small (40 pint rating) dehumidifier in the basement.

    The furnace blower was on the highest speed (factory default) tap. I've changed the blower speed tap to a lower setting and may have gotten a minute or so extra run time.

    Any other ideas?

  2. #2
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Sounds like you covered the options well.I'd have a Pro test the static ,and compare to the fan data chart,setting it for 350 cfms ,per ton.

    Other than that,load calc and replace at least the outdoor unit ,if it's a match for indoor coil,you could use the existing one.

  3. #3
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,232
    Originally posted by bobt
    The air conditioning normally runs about 5 minutes per cycle.

    I already have a small (40 pint rating) dehumidifier in the basement.

    The furnace blower was on the highest speed (factory default) tap. I've changed the blower speed tap to a lower setting and may have gotten a minute or so extra run time.

    Any other ideas?
    Get a real dehumidifier like a 100 pint Santa Fe or Ultra-Aire. Connected to your a/c, they will keep your your home <50%RH no matter what size the a/c. The most ideally sized a/c will not keep your home dry during wet cool weather. So keep your old a/c and get a real dehumidifier. These dehumidifiers remove 2-3X as much water with less electricity. thermastor.com

  4. #4
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,567
    The best or should i say the most effecient way is to upgrade to a properly sized cooling unit. I would click on the bullseye on this site and do a real load calc. I have a 2 story 2000 sf home in Connecticut and i have 3.5 in wall and maybe r-20 in attic since i had to remove alot of insulation to put down wood floor for storage. I have a 2 ton unit and i am able to drop the home 15 degrees and humidity gets below 40%(too dry). I keep my stat set for 75 to 78 and we are really comfortable.
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

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