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        Exhaust Fan Question Sign In/Join 
        posted
        So I just got done repainting our bathroom because of brown mold growing on the walls / ceiling above the shower. I have checked out the exhaust fan and noticed it wasn't pulling any air. Climbed up inside the attic crawl space and disconnected the exhaust duct and fan now pulls air. When I checked the exhaust duct, water came pouring out at the joints. This is an non-insulated crawl space so I know the water is coming from the exhaust condensing and was more than likely my cause for the fan not pulling any air. My question is this though. While up there, the exhaust for both second floor bathrooms go through the same side vent which is located about 16 feet away for the first fan and 20 feet away for the second fan. The builders used the metal flex hose to route the fan to the side wall vent. Is it worthwhile to separate the exhausts of both fans and run them to the rear wall of the house (lengths would then be 4' and 8')? Would that reduce moisture build up inside the duct? Or would other options be better (replacing flex duct with solid duct, installing an automatic timer for the fans, simply insulating the ducts better)?

        Some more information on our house if needed:
        Master bathroom (where the mold was growing) - 72 sf, 70 cfm fan
        Main bathroom - 45 sf, 50 cfm fan

        Thanks
         
        Posts: 2 | Registered: Jan 04, 2014Reply With QuoteReport This Post
        Picture of Jaybee
        posted Hide Post
        Everything you are scoping out would be a good idea. General guidelines for fans is to have no more than 15' of solid 4" vent. every bend counts as 2'. Granted, you can go a little further and it will still work but it's efficiency will be cut down.

        Flex pipe will not work as well as solid.

        Never a good idea to combine multiple vents into one unless you go up in size. Here too, under most cases it will work OK but if more than one fan is operating at the same time it will not work well. Plus, there will be backblow from one fan into the other - even with a flapper.

        So if you can reduce your runs from 15'/20' with flex line to 4'/8' of solid, you will likely solve your problem.


        Jaybee
         
        Posts: 10452 | Location: Knoxville, Tennessee | Registered: Sep 27, 2003Reply With QuoteReport This Post
        Picture of Conrad
        posted Hide Post
        If it is really cold in your attic, the vent should either be insulated or run it under your insulation. (This is where ours runs, under insulation)
        This above location can cause moisture to freeze in the vent, and leak out when it thaws...causing problems including water damage to ceilings.
         
        Posts: 6894 | Location: Plains and Mountains | Registered: Sep 26, 2003Reply With QuoteReport This Post
        Picture of Frodo
        posted Hide Post
        run your vent straight up to the ridge vent.using 1 90 on the fan body.looking straight up..no turns not bends
        you want the steam to go out, if you turn the pipe the steam will cool at that point and puddle
         
        Posts: 4089 | Location: I live in southern mississippi | Registered: Jun 01, 2008Reply With QuoteReport This Post
        posted Hide Post
        Thanks for all the information. Based on what I know about the builder, it looks like the easy route was chosen as they didn't have to deal with the soffit with the venting which is why they went to the farthest wall when they laid the ducts down. It also explains why there is only one outside vent compared to two.

        We didn't have an issue in the past but since my folks moved in with us, we are using both bathrooms more frequently. Looks like I will be fixing that this spring when the weather warms up.
         
        Posts: 2 | Registered: Jan 04, 2014Reply With QuoteReport This Post
        Picture of Frodo
        posted Hide Post
        mind if i add a little something ****
        if you do as conrad suggests,,,that is ** coverr the duct with insulation
        make sure it is sloping ** the out doors..
        the reason being...your fan pulls steam out of your bathroom
        steam is a vapor,when the ambiant temp cools the steam will turn back in** water...if your pipe is laying on the joists it will puddle and accumulate till it drips down ** your floor. if not run on an angle
        steam rises by its own accord, and disapates, so it is my oipinion ** run your vent straight up, ** a ridge vent. no offsets except the 90 degree turn on the fan itself..install piping as you would a dryer veny with no screws just silver backed duct tape..[the steam can collect on the screw ends and drip back ** the fan]

        this flaging of the word "two" is really upsetting me!!!!!!
        i like the word "two" its a handy word
        aint never done me no wrong..

        This message has been edited. Last edited by: Frodo,
         
        Posts: 4089 | Location: I live in southern mississippi | Registered: Jun 01, 2008Reply With QuoteReport This Post
        Picture of Conrad
        posted Hide Post
        You are right Frodo. I ran our vent tube horizontally and under the insulation and created a vent box in the in the soffit area w**** it could exhaust.
         
        Posts: 6894 | Location: Plains and Mountains | Registered: Sep 26, 2003Reply With QuoteReport This Post
        Picture of Conrad
        posted Hide Post
        What the heck is with the random asterisks?
        A S T e r i s ks....in case this word causes more of them.
        They seem a bit random, and of course make no sense.
         
        Posts: 6894 | Location: Plains and Mountains | Registered: Sep 26, 2003Reply With QuoteReport This Post
        posted Hide Post
        oh my my my, what a potty mouth Big Grin
         
        Posts: 984 | Location: No. California | Registered: Mar 24, 2004Reply With QuoteReport This Post
        Picture of Conrad
        posted Hide Post
        Okay, thanks for the clarification, GardenSprite. And Re-modlr this is a Bathroom forum, so Potty mouth is rather appropriate?

        Anything to reduce the spammers is good news to me, Thanks again GS!
         
        Posts: 6894 | Location: Plains and Mountains | Registered: Sep 26, 2003Reply With QuoteReport This Post
        Picture of GardenSprite
        posted Hide Post
        Conrad, Jaybee is responsible for this latest success.
         
        Posts: 1949 | Registered: Oct 06, 2006Reply With QuoteReport This Post
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