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  1. #1

    Default Bathroom Exhaust Fan - help with problem

    The bathroom in our home is relatively small - 11x15 - and since we moved in, we've had problems with shower condensation. A 10 minute shower leaves the entire place dripping in water. Even the stuff in the medicine cabinet has condensation on it.

    The fan is bottom of the line, but still rated for a bathroom larger than what we have. It exhausts to the outside and I've checked that the ducting and outside flap and all in working order - and they are.

    I just don't understand why it is such a problem. I've been in larger bathrooms with the same brand and size of fan and it works perfectly well.

    My only solution at this point is to just upgrade to a fan that is rated for a much larger space.

    Is there something else I should be checking for?

  2. #2
    Join Date
    Apr 2008
    Location
    Houston, TX
    Posts
    62

    Default Re: Bathroom Exhaust Fan - help with problem

    It could very well be the size of the fan...but before changing it out, it could also be several other things... You said you checked the vent piping and outside flap, and they seem to be okay...did you do this with the fan on to see if a decent amount of airflow come out? If the airflow seems small, check that the fan motor is spinning at a normal speed, and that the flapper inside the fan housing itself is not stuck. If either of these are a problem, most home centers carry replacement parts. If the airflow is good, it could be the type of shower head that you have. Some heads put out more of a "mist" than a "rain." They can make for a nice shower, but they put a lot more moisture in the air. If none of this works, ensure there is air available to enter the bathroom. The fan has to pull air from somewhere to exhaust it to the outside. If the bathroom is like a sealed box when you are taking a shower, you might consider trimming a little off the bottom of the bathroom door, or leaving it cracked open a little bit to allow air to come in.

  3. #3
    Join Date
    Aug 2007
    Location
    The Great White North
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    4,045

    Default Re: Bathroom Exhaust Fan - help with problem

    When taking a shower .... adding warm water vapor and mixing with the relatively cooler air into a room will create condensation..... it's the law of nature.
    So for benefical reasons this moisture needs to be mechanical exhasted ( vented ) and usually done by a bathroom exhaust fan.

    The biggest mistake people make is not running the fan for at least 20 minutes after to continue removing the excess humidty introduced by the shower.
    Bathroom fans connected to light switches start running when the light is turned on. In this situation users turn the light off before all the moisture is exhausted after a bath or shower.
    Use a delayed fan shut-off to keep the fan running for 20 minutes after you leave the room. You can use electronic or mechanical timers or humidity sensors .... or a combination of both .... to control the fan.

    Many people have the misconception these fans will remove this condensation immediately. Unless you have a huge industrial sized exhaust system this will never happen .... rather the bathroom exhaust fan will be removing a portion of this condensation during the duration of the shower.
    Unless you have a thick cloud of condesation it's likely the fan is working .... how well and how much it's exhausting is something that needs to be determined.


    There are guidlines that have been established by the Home Ventilating Institute ( HVI ) determinig the ventilation of bathrooms. Basically this recommends how many cubic feet per minute ( CFM ) of air should be vented for the size and number of fixtures for the bathroom.
    Venting the air out using a bathroom exhaust fan also requires the same amount of air to be replaced .... known as air exchange. If this doesn't occur the exhaust fan wouldn't work very well.

    The HVI recommends 1 CFM per 1 square feet for the bathroom venting.
    They also recommend considering the number of fixtures toilets , tubs , showers for large bathrooms over 100 square feet based on the following :

    toilet = 50 CFM
    Shower = 50 CFM
    Bath tub = 50 CFM
    Jetted tub = 100CFM.


    These values are determined with a recommended 8 air exchanges per hour.

    Based on the size of your bathroom ..... 11x15 = 165 square feet.

    This would mean the bathroom fan would need to be rated at 165 CFM .

    In situations such as this it's recommended to use 2 bathroom fans . Common sizes of bathroom fans range from 50 CFM - 100 CFM with the larger placed near the shower and the smaller could located near the toilet ... for example.... or at least one fan 150 CFM.

    As the previous poster mentions there may be issues with restrictions for air flow that should be checked.

    Ducting can affect fan performance..... uninsulated, undersized, or droopy flex ducting, ineffective or dirty backdraft dampers and exhaust louvres can cut rated airflow by more than 50 per cent.

    Straight short duct runs with few turns will provide highest air flow.
    For bathroom fans use duct with a diameter of at least 4 in. For long runs use larger diameter 6 inch to improve air flow. It is usually best to avoid fans with 3 inch exhaust ports and ducts.

    To find out if your exhaust fan is drawing air ........... hold a piece of toilet tissue up to the grill. The exhaust air should hold the tissue tightly to the grill. You could also check the outlet to make sure the air is leaving your house.



    Yikes ... this post is getting long winded.


    Hope this helps.
    "" an ounce of perception -- a pound of obscure "
    - Rush

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