Bathroom moisture during shower

Discussion in 'Shower & Bathtub Forum & Blog' started by Smilloy, Oct 13, 2021 at 8:12 PM.

  1. Smilloy

    Smilloy New Member

    Joined:
    Nov 26, 2014
    Location:
    Ontario
    We renovated a bathroom about a year ago, and have noticed that when the kids shower the room gets very foggy. (mirrors fogged, dripping on walls etc). I have seen lots of bathrooms with foggy mirrors etc but never dripping down the walls.

    The room is approx 6'x9' with 9' ceilings. The tub is all open to above with only a curtain rod.
    Originally I had a 110 CFM fan running through a 4" duct, and it was fogging up. (got so bad that water actually dripped from the fan)

    Swapped to a 6" duct, no change.

    Swapped fan from 110cfm to a 150CFM fan and its better, but honestly not perfect. Still lots of moisture on walls etc.

    There is no problem with duct. (replaced). Its about a 15-20' run straight outside.

    Everything I read online says that 150cfm should be well above what this size bathroom requires.
    What I am wondering is if there is too much airflow into the room (AC) which is cooling the walls too much causing condensation when the hot shower runs.

    Just doesnt add up to me. I have other bathrooms with 90cfm fans that have no issues other than the mirror fogs up for a short period.

    The only other thing I can think of to fix this is the shower needs an enclosure to keep all the hot air inside the doors rather than into the room.
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    How much room is there underneath the doorway? TO move the air, you have to have air coming in! While rare, a super tight house might not leak enough air in without a HRV (heat recovery ventilator). 6 Best Heat Recovery Ventilator Reviews 2021 - HouseholdAir If things are really tight, a bigger fan will just create more of a vacuum and not really move much air.

    Also, what is the duct configuration? If corrugated, flexible one, versus solid metal, those can slow the air flow down...you'll get more air flow with a smooth duct with minimal elbows.

    Kids, especially teens, seem to be known for very long, hot showers which doesn't help matters.
     
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  4. Smilloy

    Smilloy New Member

    Joined:
    Nov 26, 2014
    Location:
    Ontario
    The Exhaust pipe is a 6" flexible pipe, however it has only one gradual bend then straight out. I really dont think this is the issue.
    Doo has about 1/2-5/8 of an inch, if closed lots of air comes in. I thought of this and tried leaving the door open 1" while they shower and had no change in results. (there is also a supply duct in the room so it can pull through the furnace as well)

    The bigger fan did make a difference, (no more dripping water from the fan) but still tons of humidity in the air. I am curious to see what happens in once the heat in the house is on instead of AC.
     
  5. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    One time in a commercial bathroom, the fan wasn't pulling any air. The door to the bathroom was tight with no gaps. I pulled the door and cut some off the bottom. Fan was fixed.

    I guess that's not going to help with this bathroom though, if the same thing happens with the door open.
     
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Sometimes the utility company will do a blower door test for free as part of their energy efficiency program (and you might be eligible for some free upgrades depending on what they discover). Buildings always have some leaks, but Canada has had some more stringent requirements on efficiency, and yours could be tighter than normal. Knowing what your air exchange rate might shed some light on this.

    Try your test with the door more open and a nearby window cracked and see if things are any better...that might tell you if you need to provide an engineered air leak to offset what you're trying to exhaust.
     
  7. Smilloy

    Smilloy New Member

    Joined:
    Nov 26, 2014
    Location:
    Ontario
    Oh my house is 70 years old and not anywhere close to "tight"
     
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    What kind of grill is on the outlet of the fan? Could it not be opening properly?
     
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