loud air noise from condo bathroom exhaust when off

[steve167]

I'm on the top floor of a four floor condo building. When my bathroom exhaust fan is off there is still considerable "wind noise" being radiated from it. I was told that it's likely the sound from the common exhaust system it feeds into(a loud fan sucking at the far end somewhere for hallway/commerical space venting -- see next). The building is a large, mixed-use structure with > 140 units. Is there anything that I can do to reduce the sound level? Is there anything I should check for that may not have been assembled properly? Will using some sort of baffle/filter material inside the intake cover help to reduce the sound level? This seemed like something worth trying but I was a bit concerned that it would cut down on the airflow when I was actually using the exhaust fan. Any other suggestions at all short of sealing up my bathroom ceiling in my new condo? j/k of course. Thanks!

[edward301]

There should be a baffle at the output of the bath fan, it could be stuck
open, or missing. It normally keeps air from backflowing when the fan is
off. If it is functioning ok, you may be to close to the central fans, and
that will cause lots of noise.

You are correct anything you do to reduce the noise will reduce the air
flow of the fan. Without being there hard to give you ideas. If the flow
of stale air in the vent system is strong it could be pulling air out your
bath fan even when off. Take a lit cigarette and get close to your bath
fan, see if the smoke is being pulled into your bath fan when off, if so
then the vent system is pulling air from your bathroom.

There are cures, have seen this before in large condo buildings.

[DanW13]

I would also suggest that you check to see if your exhaust line is secured all the way from your exhaust fan to the point where it is connected to the others should that be the case as there maybe some vibration going thru the hard or flex ducting and it maybe causing a slight vibration, also the backdraft damper would contribute to this as well. check to see if the line is insulated as well if it is not a flex line is always a good thing to check and make sure all your connection are sealed properly.

[steve167]

So I was at my condo today and got a chance to check out the exhaust intake. Without even removing the cover I could tell immediately by feel that it was indeed pulling air even when my exhaust fan was off... so much that I almost wonder how much extra airflow the electric motor on my personal unit adds itself when turned on. I suspect that based on my basic knowledge of the "flap" that blocks backflow(if there is one) it is always going to be open since there is essentially always "suction" from the system at large -- holding it open. I'm going to check with the neighbor in the unit next to me and see if they have the same condition. Any other advice? Would I be best off checking with the builder first and then maybe an HVAC professional? The builder is still present as they have a few more units yet to sell. I also have a home warranty. Although I suspect the area above the ceiling where the exhaust vent is may technically be "common" area.

[edward301]

A simple but effective cure is to glue on a small washer to the baffle, to help
keep it closed. You will not loose efficiency since air is being sucked out
already. Do not glue on a big washer, a small on just heavy enough to
keep your baffle closed. Glue washer on at the lowest point of the baffle.

Will not cure all, but will help.

[steve167]

I'm not one for dredging up old threads but I happened across my bookmark for my original posting and thought i'd comment...

So oddly enough a contractor was out to do some HVAC work on the roof of the condo building a week or so ago(this is like a year later after my post) and sure enough, there was something "misconfigured" from the original HVAC installation when the building was completed just over a year ago. I had long since just learned to deal with slight noise and really had forgotten about it. Well now it's dead silent. Go figure.

So weird that I came across the bookmark for this post only a week or so after this "fix" occurred... seemed like I just had to post this.

[6094dan]

it sounded like the bath exhausts in your building are attached to a common duct with a booster fan that someone might have adjusted or shut off. if there is no more suction when your fan is off that should save you some $ . that ductwas sucking out your heat/ac.