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Thread: Fan condensation - stumped pls help

  1. #1

    Default Fan condensation - stumped pls help

    Everyone is stumped. I remembered Terry Love Plumbing and this forum from when i was doing a design project years ago ...and thought if this can be resolved this is the place to get the solution! I have alread done some searches of the forums but have not found anything more than we've already done. Stumped. Please help.

    New construction with 8'8" x 14' 8" bathroom with fan condensation dripping on the floor and ceiling and walls. To date, here has what been done to try and address the problem:
    - 157 cfm panasonic fan
    - pitched metal pipe to exterior about 9' long
    - insulated the pipe
    - sealed gaps at fan

    These actions improved but did not solve the situation - although it is somewhat less and can be intermittent depending upon the time of day etc (perhaps temperature changes dewpoint?). It appears, from observing, is tht the condensing is occuring at the fan housing ( obviously can't see the pipe now that it is fully insulated).

    The shower is 43 x 48 tiled with glass walls/door that stop about 12" short of the ceiling. The shower head is the serenity shower panel (Valore from Costco).

    At this point, the contractor is thinking the showerhead may be the issue - I find that odd since others have this showerhead with out similar problems.

    All suggestions more than welcome.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    What kind and amount of insulation is there in the attic? How much is there on top of the fan and ductwork? What size ductwork did you use? Are you sure that the vent cap is fully opening?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3


    jadnashua - yes the vent cap is fully open when the fan is running. There is about 24" of insulation - both batt and cellulose. Ductwork pipe is 6" .

  4. #4
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona


    If it is on the walls and ceiling, then it is an insulation problem causing the wall temperature to be below the dew point of the air in the shower.
    Licensed residential and commercial plumber

  5. #5
    ACO Shower Drain Sales johnfrwhipple's Avatar
    Join Date
    Jul 2009
    North Vancouver, BC
    Blog Entries


    Could the problem be air flow coming in from the outside? Perhaps switching out the style of or location of the vent grill might help?

    Odd problem - wish I had some experience here.

    I would try and rule out any airflow coming into your home via the piping of the fan.

    It might be possible to add some kind of wind shield or wind screen to test out this theory....

    Good Luck.

    Another crazy idea might be to try and keep the fan and duct line warm - or warmer. MAybe a simple pipe wrap heater will solve this issue for you.


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

  6. #6
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona


    IF the condensation were in the fan duct, then the water would ONLY drip from the fan, but he states tnat it is on the wall and ceiling, however, condensation ONLY occurs on surfaces which are colder than the water's dew point.
    Licensed residential and commercial plumber

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