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Thread: Condensation

  1. #1
    Join Date
    Jul 2005
    Posts
    3
    Hi all, I searched the forums but could not find a suitable answer. Here is my problem: I recently finished my basement (house is 7 years old) and discovered some stains on the new suspended ceiling tiles. It is being caused by a hvac duct that is sweating. This has not happened before finishing the basement and the basement is very dry.

    It has been very hot and humid here in Maryland recently. My theory as to why the duct is sweating is that particular duct passes directly over the main return duct for the hvac system. Several returns from my upstairs bedrooms pass right in this area causing it to be slightly warmer and enough of a temperature gradient to cause the condensation.

    My first course of action was to remove several ceiling tiles to get ventilation and blow a small fan up toward the area to try to normalize the temp. It continued to sweat, so I popped more ceiling tiles out and insulation with fiberglass all around the main return and then insulated the 6" duct that has been sweating with a 5 foot fiberglass wrap.

    It is still sweating, matter of fact it is sweating farther down the duct as well. Does anyone have a solution/suggestion before I call professional in? BTW, I did add 1 supply duct in the main run and 1 cold air return in the basement. A friend of a friend does hvac work for a living and he said that would be fine to do.

    Thanks in advance

  2. #2
    Join Date
    Mar 2004
    Location
    NJ
    Posts
    1,214
    there is no such thing as a "cold" air return. duct is probably sweating because before it was in conditioned space whereas now it is not as it is between the basement ceiling and the drop ceiling with the tiles.

    i would call a pro as adding ducts etc can cause the system's air pressure to be unbalanced. If you did add a return in the basement then this can cause the basement to be depressurized and may actually suck carbon monixide back into your home thru your gas vent pipe of your hot water system or boiler.

  3. #3
    Join Date
    Jul 2005
    Posts
    3
    Thanks for the advice. I'll seal the return up completely until I can get professional help. Sorry for the terminology mix-up in regards to the "cold air return". I guess I'm just repeating what I've read.

    Any possible solution to the condensation build-up?

  4. #4
    Join Date
    Mar 2004
    Location
    NJ
    Posts
    1,214
    condition the space the duct is located in but again this affects the air balance of the system.

    http://hvac-talk.com/vbb/showthread.php?threadid=81113

    This thread will give you more of an idea of why positive pressure is needed in a home.

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,646
    Measure the %RH and temperture in the condensing area. When insulating duct, use closed cell insulation. Moist air penetrates open insulation and condenses on the cold surface. If the basement has high humidity, suggest dehumidification, <50%RH stops condensation on 50^F duct.

  6. #6
    Join Date
    Jul 2005
    Posts
    3
    Originally posted by thehumid1
    condition the space the duct is located in but again this affects the air balance of the system.

    http://hvac-talk.com/vbb/showthread.php?threadid=81113

    This thread will give you more of an idea of why positive pressure is needed in a home.
    It's funny you should mention positive pressure. I definitely have negative pressure in the basement. At the top of the basement stairs is a regular door with a small cat door cut in the bottom of it. When I walk up the stairs, I have always noticed the blast of air coming through the cat door.

    Should there be more registers downstairs? There was only one installed by the builder and I added a second one. BTW, I did completely block of the return I put in.

  7. #7
    Join Date
    Mar 2004
    Location
    NJ
    Posts
    1,214
    Originally posted by hlweyl
    Originally posted by thehumid1
    condition the space the duct is located in but again this affects the air balance of the system.

    http://hvac-talk.com/vbb/showthread.php?threadid=81113

    This thread will give you more of an idea of why positive pressure is needed in a home.
    It's funny you should mention positive pressure. I definitely have negative pressure in the basement. At the top of the basement stairs is a regular door with a small cat door cut in the bottom of it. When I walk up the stairs, I have always noticed the blast of air coming through the cat door.

    Should there be more registers downstairs? There was only one installed by the builder and I added a second one. BTW, I did completely block of the return I put in.
    Without my cristal ball I cannot tell. you need a pro to check the airflow of the system. also the rh as teddybear mentioned.

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