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  1. #1
    Join Date
    May 2005
    Posts
    47
    I had a Carrier Infinity system installed a couple months ago (58MVP060-14 and 38TDB037), and ever since, I've had duct sweating problems that I never had before. I posted on this before, but now have more information and possible solutions

    I live in a two-story house with finished basement, and there is no door between the basement and first floor. The temperature in the house is 75 with 48% humidity, but the basement is at 65 with 63% humidity. This is actually the same dew point (53F-54F), though, so the basement isn't damp but just cold.

    The uninsulated supply ducts in the basement are sweating like crazy. I've got puddles of water and some rotten wallboard where a duct goes between the basement ceiling and the floor.

    The duct sweating never happened before with the old system. I figure the new system is either removing more heat (and hence the supply air is colder), or the airflow is less and therefore a greater temperature drop, leading to cold ducts and condensation.

    I think I've isolated the problem. Even with the Infinity Control set for AC airflow to Maximum rather than Efficiency or Comfort, the airflow never goes to 1200 CFM but stays at 1050 on my 3 ton unit. I assume my old single-stage unit was at 1200. If I could get it to 1200, it may be enough to stop the sweating. Does the Infinity Control always override the switches on the furnace control board? Or could those be set wrong? The installer says they're set correctly, but I still never get to 1200.

    I'm planning on insulating as much of the ductwork as is accessible even though I didn't think it was typical to insulate ducts in conditioned space, and I've got the supplies in the basement closed to try to keep the temperature up down there. (There is a return in the basement that is open.) Any other suggestions? How can I force the airflow to 1200? Is it normal for a basement to be this cold without any supplies open?

    Thanks for your help. The installer doesn't have any suggestions.

    [Edited by kcb203 on 07-26-2005 at 09:15 PM]

  2. #2
    Join Date
    Feb 2004
    Location
    cocoa fl
    Posts
    143
    the ducts need to be insulated plain and simple.

  3. #3
    Join Date
    Mar 2005
    Posts
    997
    In an conditioned basement I would not bother to wrap the duct. I would however by a dehumidifier to get the humidity down. This will stop your duct from sweating.

  4. #4
    Join Date
    May 2005
    Posts
    47
    I fiddled with the switches on the furnace and the airflow is now a full 1200 cfm. Perhaps the Infinity doesn't totally override the furnace settings.

    Hopefully this will stop the sweating. I also bought a dehumidifier to get the problem under immediate control and to keep the ceiling from falling in. (It's hard to insulate wet ducts with the system running and keeping them wet, but I don't really want to turn it off to do the job on a day when it's 98F.)


  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,396
    I'm with drk. Get the humidity down in the basement. 63% can grow mold & other nasties!

  6. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,063
    Originally posted by kcb203
    I live in a two-story house with finished basement, and there is no door between the basement and first floor. The temperature in the house is 75 with 48% humidity, but the basement is at 65 with 63% humidity. This is actually the same dew point (53F-54F), though, so the basement isn't damp but just cold.

    The uninsulated supply ducts in the basement are sweating like crazy. I've got puddles of water and some rotten wallboard where a duct goes between the basement ceiling and the floor.

    The duct sweating never happened before with the old system. I figure the new system is either removing more heat (and hence the supply air is colder), or the airflow is less and therefore a greater temperature drop, leading to cold ducts and condensation.

    I think I've isolated the problem. Even with the Infinity Control set for AC airflow to Maximum rather than Efficiency or Comfort, the airflow never goes to 1200 CFM but stays at 1050 on my 3 ton unit. I assume my old single-stage unit was at 1200. If I could get it to 1200, it may be enough to stop the sweating. Does the Infinity Control always override the switches on the furnace control board? Or could those be set wrong? The installer says they're set correctly, but I still never get to 1200.

    I'm planning on insulating as much of the ductwork as is accessible even though I didn't think it was typical to insulate ducts in conditioned space, and I've got the supplies in the basement closed to try to keep the temperature up down there. (There is a return in the basement that is open.) Any other suggestions? How can I force the airflow to 1200? Is it normal for a basement to be this cold without any supplies open?

    [Edited by kcb203 on 07-26-2005 at 09:15 PM]
    Forget about residential dehus, they are unable to remove much moisture at 65^F temperature. Only the best of dehumidifiers like Santa Fe/Ultra-Aire will beable to function efficiently at 65^F. You must warm the basement temperature and lower the dew point to avoid condensation on ducts and exterior wall surfaces. Rot and mold will follow extended wetting. Extreme cold duct is over-cooling the basement. Raising the air flow will warm the duct surface but raise the dew point of the supply air decreasing dehumidification. Insulation needs a air-tight moisture barrier on the exterior or the insulation will get wet. Mixing cold basement air with house air also warms the basement. A high eff. dehu ducted to take house air from your a/c return and discharge the warm dried air into the basement will lower the basemet dew point 10^F and warm the basement 3-5^F. This alone may stop the sweating. TB

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