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Problem with AC ducts in unheated attic


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  • Problem with AC ducts in unheated attic

    I have a situation I have been wrestling with for years. Below is a description of the problem and my current solution which I do not like. Can anyone think of a better solution?

    My house is a ranch. Heating is baseboard hot water. There is a whole house AC system with the AC vents in the ceiling. The ceiling vents connect via flexible duct to a rigid duct (3 feet square) and air handler in the unheated attic. There is substantial insulation in the attic equivalent to approximately R50.

    Problem: In the winter, I close the dampers in the ceiling vents. However a small amount of heated house air does leak past the dampers and flow into the attic ducts. Since the attic is unheated, the warm house air will meet the cold ducts in the attic and moisture in the air will condense causing water to collect in the ducts.

    My current solution: To prevent the moist house air from entering the attic ducts, in October I go into the attic, disconnect the flexible ducts from the ceiling vents, and cover the vent openings in the attic with lots of insulation. In June, I reverse the procedure, and go into the attic and reconnect the flexible ducts to the ceiling vents.

    I would love to stop having to disconnect and reconnect the flexible ducts. Getting around in my attic is not easy.

    Is there a better solution?

  • #2

    no metal register is going to be 100% air tight unless its seal surfaces are lined with rubber or foam rubber. could you get hold of a motorized louvered damper that you could install in your main line outlet?


    • #3
      Use roll fiberglass insulation and cover the vent and duct line with it, if condensation is happening then these two areas are not insulated well enough. I say roll insulation as it's probably easier to work with. There is probably no urgent need going all the way over the main trunk line but if you want it's certainly a good idea, covering the ducts and vent essential.
      Little about a lot and a lot about a little.
      Every day is a learning day.


      • #4
        I have no issues with ac ducts but only need help regarding air duct cleaning, anyone here can share the right ways to do it.
        Last edited by admin; 10-22-2020, 09:53 PM.


        • #5
          • Vacuum your intake vent. Run your vacuum over your vent intake to eliminate dust and dirt.
          • Wipe down your intake vent. Remove your intake vent and wipe down both sides with a wet rag to get rid of interior grime.
          • Clean between the vent blades.