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Thread: Condensation

  1. #1
    We are in the process of finishing our basement. Part of the work was to replace our old AC and Furnace with a new top end Lenox system. After installation, we have had a horrible time with condensation on the supply ducts in our basement. It has gone so far as to begin to ruin our new drywall. Our installer keeps saying that it will get better but there is no sign of improvement after 3 weeks. I have stopped the basement project until I determine if we can get the condensation under control. My old system never had this problem. Any ideas? Thanks.

  2. #2
    Join Date
    Aug 2006
    Location
    High Point, NC
    Posts
    155
    The surface of the duct would be at dew point to sweat. I do not know what part of the country you are in, but it sounds like you have a humidity problem in your basement or the air is to cold in the ducting. What is the temperature split across the cooling coil? What is the humidity level in the basement? A dehumidifier in the basement will remove the humidity and dry out the basement. This should change the dew point and the ducts should quit sweating. I would not do that until I was sure that the system was operating properly. To cold of air can cause the same problem.

  3. #3
    Join Date
    Jul 2006
    Posts
    1,091
    My old system never had this problem. Any ideas?
    New unit the same size?



  4. #4
    Join Date
    Aug 2006
    Location
    W.Va.
    Posts
    70
    is the duct work wrapped? here the duct work that needs wrapped is in the attisc, according to code

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,437
    You want a basement that is dry enough to avoid condensation on the basement a/c ducts. Close all outside vents and cover the earth in any ajoining crawlspace to stop outside moisture from entering. You are depending on the a/c to dry the whole house. Warming the cold air temp will reduce the dehumidification by the a/c. Check the %RH of the home and the basement. On a hot day, the a/c should maintain 50%RH in the home by removing 80-100 pints per day. In the basement, the %RH will be higher because the air temp is lower. You need 50%RH in the basement to avoid condensation. With cool wet weather the a/c does not run long enough to dryout the home/basement. This is when you need a good dehumidifier. Get a high eff. 90 pint/day unit like the Santa Fe to keep the home/basement dry when a/c is not running enough. Your home/basement will be more comfortable and not develoe that typical basement odor. The Dehu TB

  6. #6
    Thanks for the replies. I've had this house for 16 years and have never had anything but a very dry basement. Never a stale musty smell unless the dog was down there after getting wet. I've never had any sign of condensation on the ductwork. Now with a new and larger unit, there is dripping water all over the top of the furnace/ac unit. The ducts are drippin water through new drywall at the edge of the ceiling outlets. I have a dehumidifier running right now to see if it helps with the problem. I'm having a hard time understanding why a new high effeciency unit is causing far more problems than my old unit. My tech is suppose to be back tomorrow to look into the system again. Thanks again for the suggestions.

  7. #7
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,582
    Why did you install a bigger unit?
    Did the contractor add ductwork for the larger unit?
    We need to know what the temp diference is between the supply and return?

  8. #8
    Join Date
    Jul 2006
    Posts
    1,091
    Now with a new and larger unit
    That's most likely the problem. Larger unit, same duct and return air equals restricted air flow, restricted air flow equals cold supply air, colder supply air equals sweaty ducts

  9. #9
    Join Date
    Jul 2000
    Location
    Louisiana , USA
    Posts
    3,280
    Originally posted by highcruising
    We are in the process of finishing our basement. Part of the work was to replace our old AC and Furnace with a new top end Lenox system. After installation, we have had a horrible time with condensation on the supply ducts in our basement. It has gone so far as to begin to ruin our new drywall. Our installer keeps saying that it will get better but there is no sign of improvement after 3 weeks. I have stopped the basement project until I determine if we can get the condensation under control. My old system never had this problem. Any ideas? Thanks.

    This is Turtle.

    If your duct work sweats one day , expect them to sweat the rest of your life.

    There is two things that makes ducts sweat.

    1] Poor or not enough of insulation.

    2] Leaking air from duct work.

    Call your contractor back and work out the problem of leaking air or poor or thin insulation for the application need for your job.

    You know you might be the new way tin knockers are going with now and that is 1/2" insulation on the inside of square sheet metal ducts. You can't put that 1/2" insulation in a damp area for it will sweat. We might have just stumbled up on it.

    TURTLE

  10. #10
    Join Date
    Aug 2006
    Location
    High Point, NC
    Posts
    155
    have them check the air flow on the new system. If you put in a larger (more capacity not physical size) unit. Larger unit on existing ducting can equal problems if not checked thoroughly. Did they run a manual J calculation to determine that you needed a larger unit? A larger unit than needed will not have enough run time to dehumidify the air and the whole house could have higher humidity. Buy a digital gauge that will give you some kind of idea about the humidity level of the house.

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