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Old 03-07-2008, 09:01 PM   #1
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New bathroom fan loud in ceiling


I just replaced my bathroom exhaust fan in my bathroom with a larger unit as the old one was weak. We were having a humidity issue so we decided to step up to more CFM. I replaced it with the Broan Model 750 as it is a combo unit which adds another light.

The problem I am now having is that this is supposed to be pretty quiet but it is pretty loud now. It seems like the extra noise is being caused by vibration. I have a loft and the bathroom corner is enclosed so I can access like you do with normal attic.

I mounted straight onto the joist as they old one was. Will using some rubber washers help with this? Is this a common problem? I've already removed the fan and tested in normal plug and it runs quiet outside of the housing. I've emailed Broan to see what they say but no response yet.

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Old 03-07-2008, 09:10 PM   #2
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I would first ensure that the fan fits corrrectly in the housing and that it is secure in the housing. Then I would ensure that the fan housing is secured to the rafter and does not rattle. If it does then I would secure it more appropriately with additional cross braces.

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Old 03-11-2008, 03:38 PM   #3
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New bathroom fan loud in ceiling


As an electrical contractor I have installed alot of bath fans and have noticed a problem from time to time. At times the damper in the ductwork can become "trapped" closed especially if "plastic flex" duct is used and this will cause a significant noise factor. If you have this "flex" type duct, try putting a short piece of rigid duct to the fan and then the flex to the rigid. This will alow the damper to move without restriction. Hope this helps

Also if I am right this fan's light assembly attaches with a "wingnut"? Sometimes the wingnut will contact a light bulb and "rattle"...Try "tweeking" the bulb holder if it looks too close to the nut.
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Old 03-11-2008, 03:50 PM   #4
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If all the other suggestions don't help, try replacing the fan with another model. CFM's is the amount of air it moves, Sones is how loud/quiet it moves the air.
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Old 03-11-2008, 04:06 PM   #5
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This shouldn't be the case unless you accidentally damaged the fan blades or shaft, but the fan could be out of balance.

I agree with others that it is more likely structural resonance (it needs to be mounted more securely and braced) or the existing ducting is not adequately handling the larger amount of airflow (check for sharp bends and obstructions in the ducting or a stuck damper).
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Old 03-11-2008, 08:52 PM   #6
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New bathroom fan loud in ceiling


Squirrel cage blower wheels work far more quietly than do the ship's propeller style, especailly in a small, confined metal box. But, they do not move as much air or move it as quickly as the prop fans do. Many of these new higher CFM units resorted to using the ship's propeller stlye of fan to move more air. Hence, the noise factor increases, regardless of vibration issues, because the air is thrusted vertically into the top of the box before it can move horizontally and out the baffle and vent.
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Old 03-12-2008, 09:31 AM   #7
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I agree with that assestment with prop fans ,however it was stated that the fan in question was a broan 750, which uses the squirel cage type. I would check the ductwork/ damper for obstructions. I use alot of the broan fans and sometimes the damper flap comes off one side of the damper housing..the plastic pins are very small...and may not be opening, causing a backup of air and the noise/vibration.
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Old 03-12-2008, 11:25 AM   #8
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What do you guys think about fans that are not located in the actual vent. But down stream as an inline duct fan?
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Old 03-12-2008, 11:45 AM   #9
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Originally Posted by Wirenut2tite View Post
I agree with that assestment with prop fans ,however it was stated that the fan in question was a broan 750, which uses the squirel cage type. I would check the ductwork/ damper for obstructions. I use alot of the broan fans and sometimes the damper flap comes off one side of the damper housing..the plastic pins are very small...and may not be opening, causing a backup of air and the noise/vibration.
Most of Arizona was built around the Broan 688 (50 CFM) and unless the homeowner wants to open up the ceiling - very few homes have crawl spaces, let alone attics - so that the box can be changed out to accomodate any of the newer and larger models, it's pretty much a fait accompli. The Lowes and ACE stores out here carry replacement motors, wheels and grills specifically for the 688 because of that issue. The good thing, however, is that the 688 motors seem to last 10 years or more. Now, Home Depot decided to abandon Broan and carry their Nu-Tone line including a $30 model that supposedly retrofits the Broan 688 and upgrades its CFM flow. Unfortunately, the stuff they give you in the package does not retrofit many of the older existing 688 boxes and so the best one can do is buy it and pirate the motor and wheel assembly out of it and adapt it into the old mounting plate.

Last edited by End Grain; 03-12-2008 at 11:50 AM.
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Old 03-13-2008, 09:02 AM   #10
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New bathroom fan loud in ceiling


Did you upgrade the ductwork to the new fan? It may be to small now which could cause the problem you describe.
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Old 03-16-2008, 03:38 AM   #11
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New bathroom fan loud in ceiling


I've also thought of doing inline fans,anybody else have any experience with this?
My bathrooms fart fan has bad bearings(only 2 years old) and the bathroom is the only place my wifes allows me to smoke indoors(had to draw a line somewhere)
Looking at new fans this week at Lowes I found a nice 150CFM model at a low Sones leve (2.5 I think) but nearly fell when I saw the price @ 177$.
I can get as many 12v squirrel cage or blower motors/fans as I need and also have access to some good cheap inlines.(100-200+CFM)
I've thought of making an inline system between my two bathrooms and powering them with a small solar panel. I might even have the stuff around here to put it on remote so I don't have to wire a switch.
Shouldn't be too hard I don't think,and noise level would be as low as you want it(good reason for extra insulation).
Dumb idea? or feasible for the homeowner with an attic that wants it all?
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Old 03-16-2008, 06:51 AM   #12
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New bathroom fan loud in ceiling


If it's $177 it better be a FanTech or really nice fan. I don't know how/if you can compare these CFM ratings. The FanTech one I have FG6XL is "500 CFM." I haven't hooked ours up yet.

http://www.rewci.com/fa6392cfminc.html

I don't think such a powerful one is necessary.

Also, FanTech has wet specific ones which I would use instead. www.fantech.net

Last edited by pcampbell; 03-16-2008 at 08:07 AM.
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Old 03-16-2008, 10:35 AM   #13
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New bathroom fan loud in ceiling


Out here, most of the bathroom fans are connected via a simple length of duct pipe straight up to a simple vent on the roof. Therefore, the fan is pulling in air and pushing it up into the piece of tin that's bent over the vent pipe and serves as a rain cover. The air can escape out either side, granted. But, when it's breezy or windy out, that movement of outside air can either help suck out air faster OR push what's trying to escape back down the pipe. Not at all uncommon for one to feel a breeze coming out of the grill over a bathroom vent fan while it's running on a windy day. Matter of fact, most bath fans - regardless of the home's age - get loaded up with dead insects, leaves, feathers and twigs from the stuff that blows around outside. You can hear the junk slapping around as it hits the squirrel cage or propeller. Unfortunately, the roof vents were not installed with screens and retrofitting them with a screen can be expensive from a labor standpoint. Some vents have several inches of foam on and around them.

My point, and I actually do have one, is that a stock ordinary bathroom fan will never perform like the exhaust fan in a restaurant's range hood does. Its induction motor is designed for energy efficiency and maximum noise reduction and therefore doesn't have the horsepower or the RPM's necessary to literally suck out the foul or damp air IMO.
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Old 03-16-2008, 01:50 PM   #14
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I believe the one I saw for 177$ was a "Broan" brand name,not sure on that.
Out of all they showed on their display,it was the highest CFM with lowest Sones level.
It also had the built in light,so that I am sure contributed to the cost.
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Old 03-18-2008, 04:51 AM   #15
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New bathroom fan loud in ceiling


Quote:
Originally Posted by pcampbell View Post
What do you guys think about fans that are not located in the actual vent. But down stream as an inline duct fan?
this is the BEST way in regards to noise level. This will be my setup when i build my house.

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