Bathroom Exhaust Fans

Discussion in 'HVAC Heating & Cooling' started by clawbennett, Nov 16, 2019.

  1. clawbennett

    clawbennett New Member

    Joined:
    May 21, 2019
    Location:
    Stanwood, MI
    I haven't been able to figure it out, so I figured I would ask here.

    Who do we call with regards to bathroom exhaust fans and their ducting? They are not pulling enough moisture out of the air in the bathrooms and attached bedrooms and we are getting condensation on the walls and windows in the bedrooms. This is now leading to mold around the windows.

    We aren't even sure if the previous owner (Also the builder) installed the exhaust fan ducting right in this multi-level home.

    Do I call a plumber being that it's a bathroom exhaust or do we call an AC/Heating company to come inspect, check ducting, and install new vents?

    Thanks!
     
  2. clawbennett

    clawbennett New Member

    Joined:
    May 21, 2019
    Location:
    Stanwood, MI
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  4. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    A/C guy. First what type of exhaust fan are they? If they're the $59 NUTONE (better known as a fart fan) they do not move that much air regardless what the spec reads. If it makes a roar while in use it is probably a Nutone with a small motor and propeller type fan.

    If you want a real exhaust fan you get one with a squirrel cage or drum fan. Panasonic is the more popular one. We have two of them in our master bath and it still takes awhile to pull out the humidity. Another issue could be not enough wall insulation. There is condensation because the wall is cold and any humidity from the washer or cooking will condense on cold walls. I know today you are getting wintry weather and colder than normal.

    But first check the duct work. Straight and rigid duct to the outside wall is best. Regardless of what you do replace the switch with a timer. This is the one I use, up to 60 minutes. the fan should run at least 20 minutes after the shower is used. I leave my at 60 minutes. The panasonic units are dead quite.
    https://www.amazon.com/Leviton-LTT6...iton+wall+switch+timer&qid=1574631307&sr=8-10
     
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  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
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    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Where and how the duct is run can affect how much air it can move. Also, in a really tight home, without engineered way to get air into the home, trying to blow some out will be less efficient.

    As to sizing, measure the H-W-D of the room to determine the volume, then multiply by 8 and divide by 60 to get the 8 air changes per hour, giving you the number of CF/M fan you need. 8-10 x air exchange is about what you need.

    Many people do not run their fan(s) long enough after completing the shower...it may need at least 20-minutes and probably more if it's undersized. Opening the door when finished can help, as it can then draw air from the rest of the home with less restrictions.

    Panasonic markets a moisture sensing switch that you might like. Some of their fans have it built-in, which is a better solution. Note, it's measuring moisture, not water vapor, so it will take dampness to get to the height of the switch before it will turn on automatically. I've found that it works better to turn it on before entering the shower. The default mode is it will turn off after about 20-minutes of turning on if not damp (i.e., if turned on manually), or 20-minutes after it senses things have dried out enough to purge the sensor, whether turned on manually or automatically.

    A fixed timer would help, but may be too long or too short, and is useless if not manually turned on.
     
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  6. dj2

    dj2 In the Trades

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    Location:
    California
    You mentioned a window, open it.
     
  7. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609

    Condensation on windows is one thing, condensation on walls is something else. It's unlikely that condensation and mold on walls in adjacent rooms are a bath fan venting problem. You may have a roof leak or screwed up window flashing details, &/or missing insulation in the affected wall areas.

    That's not to say it isn't worth verifying that the bath fan installation is up to snuff.
     
  8. clawbennett

    clawbennett New Member

    Joined:
    May 21, 2019
    Location:
    Stanwood, MI
    No roof leaks causing the molding issue.

    we typically run the exhaust fan when showering. And even after for a while until visible steam is gone from the bathroom, but the moisture and condensation still remains both on the bathroom ceiling and connected master bedroom windows and wall. It is an exterior wall. Air temp outside of the home is often much cooler than inside the home (Michigan).

    we have no access to the duct work in the master bathroom without tearing the ceiling out. That is our main concern. We are trying to determine where the duct goes. It’s between the main floor and second floor. So we are trying to make sure it’s not dumping into the ceiling somewhere.

    I have found some smoke testing devices that emit smoke in the vent to trace it. Does anyone know what size of these we would need? They’re sold based on the cu ft size. Not quite sure how to measure what we need as I’m unsure what Cu Ft measurement they are asking for.

    as for the $59 Nutone, I’m almost confident that’s what it is and it is undersized for the size bathrooms we have. We will be replacing them for sure, but it’s the ducting we are mostly concerned about. No visible ducting for the main trouble area (master bath).
     
  9. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    There are some <$50 fiber optic duct/drain inspection cameras with 25-100' of cable that use smart-phones as displays that might be worth trying out here.

    Even if the duct is routed correctly, if a section has come un-done and is leaking into a joist bay the moisture could go pretty far and wide (potentially with a lot more mold inside the framing bay than would be visible in the rooms.)
     
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  10. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    If there is no outside wall vent at the level of the 2nd floor joist, then there is none or it goes up into the attic space above the second floor and maybe out the roof. If it does these fans cannot push air that far let alone in height.

    upload_2019-12-16_20-46-41.png
     
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