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bathroom venting and fan size

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  • bathroom venting and fan size

    I recently installed and exhaust fan I'm my bathroom. The fan was rated 100CFM (which was more than adequate for the small space).

    Because of the layout of the house I had to run 2' of straight 6" smooth-walled venting, followed by 2 90° turns into approximately 15' of 6" smoothwalled round venting. The venting ends out of a gable wall, covered by an insect screen and decorative grille.

    When I installed I called the manufacturer to determine if there was a limit on the length of the exhaust venting. The customer service person (who was quite rude) simply repeated that the only requirement was that is a 2' straight section immediately after the unit.

    Yesterday the unit stopped functioning. I checked wiring and all is good, so I'm assuming something may have burned out.

    Is it possible that the length of exhaust placed too much strain on motor? If this is the case would a more powerful motor (high cfm I guess) address this?

    Any other ideas?
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  • #2

    Re: bathroom venting and fan size

    I would rather doubt it had anything to do with venting. Using 6 in pipe is more than is required , at least on the last job I did 2 years ago. Anything over 110 cfm was required to be 6 inches. Less than 110 cfm 4 inch met the code. Using 6 in is a good idea for 4 inch as it creates less back pressure. I am not sure you can use the flexible pipe anymore. I know for certain you can not use flexible pipe in kitchen hood vents. My friend has my new OBC.

    Brian
    If your dreams don't scare you, you are not dreaming big enough

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    • #3

      Re: bathroom venting and fan size

      Actually reducing the flow by adding exhaust ducting will reduce the amps the fan draws. Big industrial fans are always started with dampers closed to reduce startup amps. However if the fan is in the air stream and relies on the airflow for cooling, the restricted airflow may have caused the motor to burn out much the same as happens with shop vacs when the filter plugs. I think a bigger fan may be the solution but I'm not sure, maybe you need to find a manufacturer or dealer that can give better advice.

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      • #4

        Re: bathroom venting and fan size

        Did you check the breaker? Is the vent obstructed with snow or anything else? Is there a reset button? Not likely but just asking.

        Venting such as you show should have a Goose neck of some sort.
        "Do it Right!"

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        • #5

          Re: bathroom venting and fan size

          Most of those have a regular plug and cord on the motor. Plug it into an extension cord and see if it works.

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          • #6

            Re: bathroom venting and fan size

            Is your bug screen icing up?

            And you may have a bad motor. I put a 110 or 150 in and it never worked right from day one. I thought it was my duct run and vent but all was good. Checked with the mfg and they sent me another motor. Voila, fixed. Original wasn’t running up to speed.

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            • #7

              Re: bathroom venting and fan size

              20190206_101319.jpg 20190206_101319.jpg20190206_101319.jpg20190206_101502.jpg Thanks for all the replies ... I opened the fan housing and found a bunch of water and water on the circuit board (pics attached)

              I'm going to assume this is the problem (unless these are somehow special motors build to be wet due to bathroom condensation...).

              Now the question is where is the water coming from?!
              Last edited by greatness; 02-06-2019, 10:26 AM.

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              • #8

                Re: bathroom venting and fan size

                That's precisely why I mentioned a goose neck in the venting pipe. Combine that with what I assume from your drawing and description is a long uphill push for the fan and an open to the elements gable screen and you have the so called perfect storm.
                "Do it Right!"

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                • #9

                  Re: bathroom venting and fan size

                  What my diagram doesn't show is that it slopes downwards towards the gable wall.

                  Also, how would water get in the motor housing? Even if it was running backwards from outside it still shouldn't touch the motor. Unless I'm missing something....
                  Last edited by greatness; 02-06-2019, 06:06 PM.

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                  • #10

                    Re: bathroom venting and fan size

                    I could suggest other things but I really don't understand your pictures in the first place I guess.

                    If you use your fan to dissipate steam you have to realize the hot steam will be water by the time you're asking the fan to push it vertically up the cold gable wall and out the vent and that ain't about to happen.
                    "Do it Right!"

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                    • #11

                      Re: bathroom venting and fan size

                      Is the vent fan and duct insulated? Maybe the moisture in the exhaust air is condensing in the duct and the blower housing.

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                      • #12

                        Re: bathroom venting and fan size

                        Doug G The whole run of ducting is insulated. The fan/motor only has insulation running about 3/4 up its height, given the limited insulation currently in the attic. I was concerned about condensation and thought about running vapor barrier over the housing......

                        The first diagram was supposed to be from above. I've done a new one that is a simplified side view that I hope is more helpful for further discussion/suggestions:

                        vent.jpg

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                        • #13

                          Re: bathroom venting and fan size

                          If that motor wasn’t running up to speed, it may not be able to clear the steam or clear the condensation in the short line and housing.

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                          • #14

                            Re: bathroom venting and fan size

                            That sketch is a lot different than your first one. You will always get better answers with a complete description of what you have. This is easy now. If the fan body iis not covered under a minimum of 6 inches of insulation it will never work right. Cover the pipe too as much as you can for as far as you can. You really should have a hood vent at the gable too.
                            "Do it Right!"

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                            • #15

                              Re: bathroom venting and fan size

                              As Rusty says, we aren't going to get anywhere with piecemeal descriptions, but to stop the guessing, include the brand (if possible) of the fan. Either the maker or aftermarket carry replacement fan motors should that become necessary. Before going further please verify if the fan stopped because it is dead?, in which case fan/motor replacements are readily available, just plug in connector. Verify that first with a simple extension cord as Bender suggests. Forget any duct investigation until the fan is verified.

                              Of curiosity, replies above assume a shower which is likely, but not stated - is this a full bath, e.g. shower/tub as well as the sink & toilet?
                              Last edited by Woodwreck; 02-07-2019, 09:40 AM.
                              Start slow; wind down gracefuilly

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