Moisture in bathroom

Discussion in 'Shower & Bathtub Forum & Blog' started by mmax, Jun 6, 2011.

  1. mmax

    mmax New Member

    Messages:
    22
    Location:
    Missouri
    I have an 80 sqft bathroom and recently installed a 110 cfm Panasonic bath fan. If the furnace or AC is on, everything is fine. If not, moisture accumulates all over the ceiling, walls, the light, mirror, window, etc. There are now water marks on the walls where the moisture has run down the walls.

    The bathtub/shower is one wall with the vanity & toilet across from it. The fan is between the vanity & toilet. I fan is on a timer and runs for 30 minutes after we turn the light off, so likely runs for an hour after shower is complete.

    Is this normal? I've used bathrooms in the past while never running an exhaust fan and never seen moisture accumulate like this.
    Last edited by a moderator: Jun 9, 2011
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,128
    Location:
    New England
    Is the house quite tight? WHen exhausting air, there has to be air coming in to provide makeup. Do you leave the doors open when finished, or close them? Is there carpeting on the floor and little gap? If I remember, there are internal controls on (at least some) Panasonic models that adjust the actual fan speed. Does yours have this? What is it actually set for? It may only be running at something like half speed. How long is the duct on the outlet? Is the damper opening, or could it be painted shut and can't move? Is it installed in the proper direction? If you're not running the a/c, and the relative humidity is way up there, it may not clear the condensation for a long time.
  3. mmax

    mmax New Member

    Messages:
    22
    Location:
    Missouri
    It's an old house with no insulation in the walls, and just a few inches in the attic above the bathroom. I doubt it is too airtight. The bathroom door is usually closed or almost closed when the shower is on, but open once the shower is off. The floor is tile.

    I do not know if it there are internal controls on the fan, but I don't recall any from reading the documentation. The fan has only been installed about 6 months.

    The duct on the outlet is not too long, maybe 3 feet. It is not insluated. It is that flimsy white stuff and the outlet hangs below a roof vent. It does not have a dedicated vent in the roof.

    What do you mean is it installed in the proper direction?
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,128
    Location:
    New England
    Adding moist air to your attic isn't a great idea. The flimsy plastic, wire formed ductwork slows the air down (but not much if it is only 3') - smooth, solid ductwork is better, and on a colder day, without insulation, you could get condensation dripping back into the room. Not all of their fans are adjustable, but some are...depends on the model. SOmetimes, when just bent over, that kind of duct essentially gets pinched off - it must be fully opened to allow good air flow. If there isn't much room beneath the door, the fan won't move a lot of air while showering, but once the door is opened, it should recover.

    Where is the fan relative to the shower?

    The fan needs a damper. It is often in the unit, but may be external. It must move freely to open when the motor turns on, and fall back closed when it is off. If, for some reason, that got crimped, or if external, is installed backwards, the airflow would try to close it rather than open it. In that case, the fan won't move much air.
  5. mmax

    mmax New Member

    Messages:
    22
    Location:
    Missouri
    Thanks for the replies. The end of the duct in the attic is about 1 inch from a roof vent, so the moisture isn't just staying in the attic.

    The fan has a built in damper but I have never checked it. If I hold a piece of paper under the fan while running it pulls it up to the grate, so I think it is pulling air out.

    The bathroom is a rectangle with the tub/shower along one long wall and the vanity and toilet along the other. The fan centered between the vanity and toilet. Not more than three feet from the shower, if that.

    I've just never seen so much moisture accumulate on the walls under any circumstance. Once it's there, even if the fan extracts it once door is open and the shower off, the damage seems to be done. The water stains are easily cleaned off the wall, but it seems there has to be a better way.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,128
    Location:
    New England
    Sounds like you may need to make accommodations to provide easier airflow into the room while showering or shorten your hot, steamy showers some!? On a cold day, that moist air will hit the colder wood and surrounds, and dampen it. This can lead to moisture damage and mildew. It is much better to actually vent it outside.
  7. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

    Messages:
    4,389
    Location:
    North Vancouver, BC
    Did you have this problem before? Have you changed anything in your home? The exterior? New Hot Water Tank? Is this a new home to you?

    The fan you have is a good one. We recommend them every day here in Vancouver - that said if the walls and ceiling are cold there is no way to prevent the steam generated from condensing on the cold surfaces.

    Jim talks about air flow and leaving the door open. Do you have a tight seal on the bathroom floor? You should check this theory first with a shower with the door closed and then one with the door open.

    Next I would invest in some more attic insulation and see the results of improving the insulation above your bathroom. This can warm up that ceiling some and help prevent the steam from condensing so quickly on the ceiling.
    Last edited by a moderator: Jun 9, 2011
  8. mmax

    mmax New Member

    Messages:
    22
    Location:
    Missouri
    We remodeled the bathroom, but mostly cosmetic changes. New shower fixtures. I don't remember it being as bad before, but I wasn't paying as much attention as it was not a concern as I knew we were remodeling soon.

    I will try a door open vs. closed and see the difference. I could add insulation, but it doesn't seem that is really the cause when it happens in all seasons.
  9. WorthFlorida

    WorthFlorida USCG escorting cruise ship leaving Port Everglades

    Messages:
    117
    Location:
    Lake Worth, Florida
    On this remodel, did you paint the walls and ceiling with a glossier paint? Was the original paint flat latex or wall paper? A semi gloss and even a satin paint will mirror the wall more so and condensation will be more noticeable. It's a harder surface and therefore the moister will lay on the wall the same as it does on the bathroom mirror. A flat latex paint will absorb more moisture and not reflect as much.

    With the fan on I would go to the outlet and be sure that there the air is flowing out. The tissue test is OK but this is a strong fan and even with a blocked up vent it could still hold up the tissue.

    You mentioned new shower fixture. Was the shower head before and after the remodel a single head or was the replacement with several sprayers. Maybe the new shower head has a finer spray and you are dumping more moisture (fog) into the air.
    Last edited: Jun 16, 2011
Similar Threads: Moisture bathroom
Forum Title Date
Shower & Bathtub Forum & Blog Tyroc Subflooring - Sound, Moisture and Uncoupling flooring prep Dec 10, 2013
Shower & Bathtub Forum & Blog Moisture barrier issue Jun 15, 2013
Shower & Bathtub Forum & Blog Moisture Resistant Dry Wall and Mastic for tub shower surrounds May 2, 2012
Shower & Bathtub Forum & Blog Evidence of moisture through the back of backer board Apr 25, 2011
Shower & Bathtub Forum & Blog Moisture on Outside of Bathtub Nov 2, 2007

Share This Page