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  1. #1
    Join Date
    Apr 2010
    Location
    Seattle
    Posts
    37

    Bathroom exhaust fan drips water

    I have an Air King 100cfm exhaust fan next to the shower. It was originally installed using 4" flexible insulated duct through the attic and out the roof and every time I got out of the shower the fan dripped water down on my head. I was frustrated and replaced it with 4" rigid insulated smooth wall ducting. From the fan I started with a 90 deg adjustable elbow which is connected to a 30" straight duct at about a 60 deg angle that attached to another 90 deg adjustable elbow (this elbow connects to the roof vent that has a damper). After doing all this work nothing has changed. The ducting is taped sealed and insulated so I completely confused. The fan works great without ducting attached I feel it push a lot of air into the attic. the fan is covered with loose fill fiberglass insulation so it shouldn't be to cold and causing it to condense. The overall distance for ducting is about 4 feet and its all smooth wall now so Im totally confused about the next step, please help!

  2. #2
    Join Date
    Jan 2007
    Location
    N.E. Ok.
    Posts
    1,369
    Is the damper on the roof vent opening with fan on?

  3. #3
    Join Date
    Apr 2010
    Location
    Seattle
    Posts
    37
    yes, when I was removing the flexible ducting I left it connected to the fan and pulled it off the roof vent then held it close enough so I could see the air pushing damper open.

  4. #4
    kenney t Guest
    100cfm is alot for 4in. don't you think?

  5. #5
    Join Date
    Dec 2007
    Location
    Cedar Grove, Wi-Sheboygan
    Posts
    1,582
    Quote Originally Posted by kenney t View Post
    100cfm is alot for 4in. don't you think?
    With a 100 CFM fan you should have atleast a 6" duct which is good for about 110 CFM's.

  6. #6
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,943
    If you are exhausting humid air from the shower into a duct that is cooled by a cold attic, the steam vapor is going to condense to a liquid and drain back through the fan.

    If your exhaust fan is dripping, you are running the fan when it shouldn't be run. Why waste all of that nice moisture that could be humidifying your home?
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  7. #7
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,006
    Just a couple of questions. The water is dripping out of the fan even when it's running? Are you sure it's coming out of the fan itself and not from around it?

    Do you have a forced air heating/cooling system in the house and is there a register in the bathroom and is the damper open so it blows air into the bathroom? Wondering if maybe the bathroom is so air tight that the fan can't move any air out when someone is in there showering with the door closed.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  8. #8
    Join Date
    Jun 2009
    Location
    Bakersfield, Ca
    Posts
    1,716

    Thumbs up

    Quote Originally Posted by carboneutral View Post
    I have an Air King 100cfm exhaust fan next to the shower. It was originally installed using 4" flexible insulated duct through the attic and out the roof and every time I got out of the shower the fan dripped water down on my head. I was frustrated and replaced it with 4" rigid insulated smooth wall ducting. From the fan I started with a 90 deg adjustable elbow which is connected to a 30" straight duct at about a 60 deg angle that attached to another 90 deg adjustable elbow (this elbow connects to the roof vent that has a damper). After doing all this work nothing has changed. The ducting is taped sealed and insulated so I completely confused. The fan works great without ducting attached I feel it push a lot of air into the attic. the fan is covered with loose fill fiberglass insulation so it shouldn't be to cold and causing it to condense. The overall distance for ducting is about 4 feet and its all smooth wall now so Im totally confused about the next step, please help!
    Put a trap in your fart fan duct right after the register. I have never seen one but it should work. Then run a 1/4 drain line at the bottom to a vent. Again, I have never seen this.

  9. #9
    Join Date
    Apr 2010
    Location
    Seattle
    Posts
    37
    thanks for the replies. I did think installing a 6" duct but the connection at the fan is 4" is there a a fitting that will allow a 4" opening to connect to a 6" duct.

    When I'm in the shower the door to the bathroom is open because I was concerned the bathroom was too air tight since it is new construction.

    I've seen fans in many homes that work at removing warm moist air and vent it out without any water dripping back, but I don't know if they were vented through the attic or the side of the house.

    Is it uncommon to vent a bathroom fan up through the attic? The metal ducting must be getting cold it's insulated but at the roof vent there is just a thin metal damper keeping cold air out which won't help any.

    I did see on Air King website that some of the models have a damper connected on the fan where the air exhausts, but I don't see how that would help since the water drips back at the end of the shower while the fan is still running, and I let continue to run for an additional 15 min.

  10. #10
    Join Date
    Jun 2010
    Location
    Charlotte, NC
    Posts
    155
    All I can tell you is that I have a bathroom vented through the roof with no problem.

    If you go outside and look at the vent with the shower running and the fan on, on a cold day, you should see substantial steam shooting out. If you don't, then the damper is not opening.

    Your vent on the roof faces down, I assume? And it is on a sloped roof with the vent sloping down so condensation on the top of the vent, where it can't be insulated, will run down to the exit, not hang there on a horizontal slope to drip back down?

    If you turn on the vent a few minutes before you take a shower, the warm air going up it should warm up the metal ductwork enough so condensation should be minimal.

  11. #11
    Join Date
    Dec 2007
    Location
    Cedar Grove, Wi-Sheboygan
    Posts
    1,582
    Make sure it's sloped to the outside, if you unable to slope it atleast get a 90 somewhere in the run and be sure to insulate the entire duct from the fan up to the underside of your roof deck sealed good at both ends. Doing this should cure your problems

  12. #12
    Join Date
    Aug 2009
    Location
    tn.
    Posts
    199
    Is the blade on the fan going the right way?

  13. #13
    Join Date
    Apr 2010
    Location
    Seattle
    Posts
    37
    I feel the duct is sloped well, but maybe I should have a short straight run come out of the fan and then to a 90 deg elbow and go straight up to the roof vent.

    I will check and see if the fan blades turn in the right direction, but it definitely sucks air up and out of the room it just traps moisture and spits it back down.

    The funny thing is the fan dripped water during the summer so I'm totally confused as to where moisture is getting trapped. Replacing all ducting should have fixed it but maybe the fan is defective and there is a pocket somewhere allowing moisture to enter and build up.

    Or maybe the roof vent doesn't open as well as it should, does anyone know of a good roof vent I could buy. I might start there since its cheaper than buying a new fan.

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