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  1. #1
    Join Date
    Dec 2009
    Location
    Central MN
    Posts
    502

    Default Bathroom exhaust fan

    Ok its slow on the site and I have a question/scenario so I am going see who knows what.

    I replaced the bathroom exhaust fan in one of our bathrooms (small bathroom) over this weekend. The old one was what I would call a traditional 4 blade fan (was loud and the decorative shroud on the ceiling was dated and looked bad). I did a little homework online and purchased a new Panasonic unit with a 110 CFM rating, this unit has a squirrel cage style fan. Nice looking and really quite. I enlarged the opening in the ceiling, found out my bathroom plumbing vent (PVC) was right next to the original exhaust fan and will be next to the new fan. Had to redo the electrical (original was not long enough). Went to install the new fan and it was hitting the plumbing vent $!@#%&!@. Ok my only option was to rotate the new fan 180 dig because of the mounting. Not the end of the world but will also need to extend the actual vent line now as that will now be 180 dig off. Old vent was 3” diameter new fan had a 4” exhaust output. Went and purchased some new 4” flexible vent and a reducer. Got everything installed, looks good. Took a shower the first night and was disappointed with the amount of condensation/fogging on the bathroom mirror (AC was running in house so bathroom was a little chilled then ya long hot shower). Yesterday I removed the fan shortened the exhaust line that I just installed to the shortest possible length (was thinking the added length of new vent might be an issue). Put it all back together, took shower again last night same issue (what I believe to be excessive amounts of condensation on the bathroom mirror). 20 year old fan was doing better job. So my question is why, new style fan just not as good, new 4” duct (about 16” total length with a 90 dig bend coming out of the new fan and then another quick 90 dig bend (no not pinched) to get back to original exhaust line to long (I don’t think it should be). Thoughts? It is exhausting out through my roof (nothing was touched there).

  2. #2
    Join Date
    Dec 2009
    Location
    se mn
    Posts
    2,132

    Default

    You would be amazed what a 90 does for restricting air flow. especially with squirrel cage fan. Needs a straight shot out IMO. Im not a plumber but have been known to be opinionated....

  3. #3
    Join Date
    Feb 2010
    Location
    Lake of the Woods, MN
    Posts
    143

    Default

    With your reconfiguration of the vent, is it possible the baffle for the vent was installed upside down? If the baffle is upside down, the weighted side of the flap may be stuck in a closed position.

    The manual of the fan should come with info about the max amount of exhaust footage allowed and how many feet a 90 elbow is equivalent to, to calculate your equivalent linear footage. But I doubt adding a single 90 is the difference in function between the old fan and the new one.

    I had the pleasure of adding a bathroom fan to my bathroom previously without one a few years ago. The 4/12 pitch roof attic space was not a fun work space, I hope you have a more comfortable work space.

  4. #4
    Join Date
    Dec 2009
    Location
    se mn
    Posts
    2,132

    Default

    Quote Originally Posted by CrossfireLOW View Post
    But I doubt adding a single 90 is the difference in function between the old fan and the new one.
    .

    Thats the thing if you read it he added 2-90's back to back. Thats a huge restriction in my mind.

  5. #5
    Join Date
    Dec 2009
    Location
    Sheboygan,Wi. Retirment home Lakewood, wi.
    Posts
    316

    Default

    Better to redo plumbing vent and install with no 90s

    - - - Updated - - -

    It would also help to hard pipe it instead of using the corrugated junk tbat comes with it

  6. #6
    Join Date
    Dec 2009
    Location
    North Twin Cities
    Posts
    1,241

    Default

    It never hurts to do a smoke test just to make sure before you dig into it too far. I like to hold the smoke just off to the side and see if it pulls the flame.
    I have seen a number of fans with the baffle not working properly. Some upside down and some that had the flex line taped to the housing. The tape was holding it shut. Shouldn't use tape, but somebody did.

    The run is pretty long especially with that many bends. Flex line will impede the flow too.
    I have also seen the flapper stick on the roof vent in extreme temps. Super hot or super cold.

    Trying to get through the simple potential solutions before the main fix. It sounds like you have reduced the pipe down to the old 3" line at some point. Is that correct?
    These fans use airflow to move air. It isn't like a pressure setup where you can reduce the pipe size and still somewhat keep the flow.
    It might be a real pain, but a straight unrestricted line will give the best flow.

  7. #7
    Join Date
    Feb 2020
    Location
    Under a rock
    Posts
    419

    Default

    This...

    and a reducer.


    Think of you trucks exhaust ...think a reducer would do anything if you went from stock to 5 inch pipe....would you want a reducer if your upgrading from stock to 5 inch pipe....would ya HP go up or down?....think man...think ....lol

  8. #8
    Join Date
    Dec 2009
    Location
    Central MN
    Posts
    502

    Default

    Thanks for the info guys

    I know the damper is working properly
    Nothing in the manual for max run length or formula about adding bends (just says keep as short as possible).

    So far I have been able to do everything from the bathroom (have not been in the attic yet).

    Ok if I need to redo the entire vent any ideas if the roof cap will be able to accommodate a 4” vent line or since a 3” is currently installed will I be SOL there to? House was built in the early 80’s

  9. #9
    Join Date
    Dec 2009
    Location
    Eleva,WI
    Posts
    632

    Default

    Don't overlook replacement air. If air can't get back into the bathroom those fans will not blow anything out.

  10. #10
    Join Date
    Feb 2012
    Location
    SC WISCONSIN
    Posts
    294

    Default

    Make sure your vent line is insulated. Also like Renegade said you need air. most of the time the only make up air in a bathroom is the gap under the door. sometimes the gap was not good enough or another layer of flooring gets added, or thick carpet in the hallway and you will not have enough make up air. flex line needs to be insulated otherwise air will turn into moisture before it is out of the vent. Also people used to just dump the line into the soffit to avoid actually having a vent to side, roof or soffit around, that is another no no

  11. #11
    Join Date
    Dec 2009
    Location
    North Twin Cities
    Posts
    1,241

    Default

    I would be surprised if a roof cap from that era would fit both sizes. The good news is that many roof caps today have nice oversized nail flanges. That makes them easier to retrofit. Just be studious about lifting up the shingles and mount the new cap correctly. Use good sealant. The job isn't too bad.

    I would use straight or smooth wall pipe if possible. Flex wall pipe slows the air flow significantly, hence the recommendation for insulation. Insulation is never a bad idea for whatever pipe you install. I recently found a flex line that was plugged from water/ice. Installer had just laid it across a low clearance section in the cold space above the garage. The condensation ran toward a low spot in the line. It was probably a good five gallons!!! The homeowner's builder suggested an unbelievable fix. (Poke a hole and use a drip tray to evaporate the water.) Wowza.

    I'm a firm believer of the theory, Do it right, do it once. It might take a little longer, but you will be done.

    BTW, the condensation will always be worst in the beginning of the fan cycle especially with showers. High moisture air and cold pipe. It really helps to run the fan with the double run time. (10 minute shower = 20 minute fan run) The longer run times balance the pipe temp and draw down the moisture levels.

  12. #12
    Join Date
    Dec 2009
    Location
    Out there
    Posts
    5,223

    Default

    yur old 4 blade fan was moving more air than yur new "quiet" squirrel cage..... you took a step backwards.

    I got a few a these clearanced out Home Depot exhaust fans I'd be able to ship to you for $89.00 USD ea.


  13. #13
    Join Date
    Dec 2009
    Location
    Central MN
    Posts
    502

    Default

    thanks for all the info guys, so much for sitting an my ars this weekend barking out orders at the wife .......should have just left the old beat up one in there.

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