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Replace Bathroom fan w/o attic access

The fan in our bathroom makes noise. It is a 20 year old builder grade unit that came with the condo. Our bathroom is in the middle of the house, no window. When we removed the fan assembly and tested it with a regular outlet, there was no noise. So, we think it is the fan housing rattling. We cannot find a direct replacement, so we would like to replace it with a newer model, more CFM and less noise. However, we have no access to the attic. The newer model has about the same size housing as the existing one which is nailed to a ceiling joist, but not exactly the same ceiling cutout. We can not even remove the current fan housing without cutting into the ceiling.

What is the best way to replace the fan housing?

A. Spruce
Re: Replace Bathroom fan w/o attic access

It's possible that the fan is actually at fault as the noise maker. As the internals wear, the shaft can "bounce" up and down, causing the vibration you speak of. Replacement of the motor or possibly having some shims installed in your current one may quell the noise. It may also be possible to replace the current blades with more aggressive blades that will move more air.

As to replacing the whole unit, that could pose a trickier task with your parameters (no damage to existing ceiling and no access from above ). You could remove the old housing with a combination of metal shears, pliers, and a few other implements of destruction. Then it's a matter of resizing the hole for the new unit, making the duct and electrical connections, and attaching it within the hole. You may have to oversize the hole a bit, just use care not to go any larger than what the fan cover will hide.

Re: Replace Bathroom fan w/o attic access

I agree with A.Spruce about the fan and motor assembly .

It's likely in those 20 years the bathroom fan hasn't been cleaned and serviced.
Most people rarely do this and it's something I do for people often.

Recently I did this for a homeowner that had 3 fans vibrating like crazy with a couple that were slow starting also .... original fans installed 1964. Cleaned and lubed them .... they run just like day they were installed.

The fan blades will accumulate crud ( a technical term ) which will unbalance the blades causing a vibration which rattles the metal housing. You might start with cleaning the blades and if they are metal careful of not bending them as this will also unbalance the fan.

The other thing is the motor assembly can be disassembled and easily cleaned and serviced. Typically these are a simple designed motor known as C-frame as seen here.

The round portion that's found on either side of the motor housing where the shaft goes through is the bearing assembly. These will get built up with crud and the lubrication for the bearings will dry out.
Remove these and you will notice the bearings are copper or brass and are meant to move .... spray some WD-40 on them to free them so they will move freely.
You will notice the bearings are surrounded with a felt packing .... this should be wetted with oil to lubricate the bearing allowing to remain movable.

These movable bearings are to keep the alignment of the shaft consistent and aid with some of the imbalance of the fans blades .... which helps to reduce vibration.

If you do want more CFM then the fan blade assembly might be changed or a whole motor blade assembly installed.

Hope this helps.:)

Re: Replace Bathroom fan w/o attic access

Thanks to everyone for the helpful answers.

The dynamics of a fan and motor are indeed different outside of a housing than inside of one. :) We'll remove the fan/motor assembly and see if it can be lubricated. If that isn't good enough, Broan-NuTone still makes replacement fan/motor kits.

Re: Replace Bathroom fan w/o attic access

Bathroom fans:
I never liked the noise from the bathroom fan, which ran whenever the light was on and usually was not needed. I did not need the fan on when combing hair, shaving, etc! I ran a line to the fan and put in a second switch just for the fan. Now the fan motor will probably never wear out and it's quiet in the bathroom!
Also installed a motion sensor switch for the light in the bathroom and loved it, though it gets dark if one is seated very long...

Re: Replace Bathroom fan w/o attic access

Love the Fantech fans Mr. asc. Nobody wants to seem to want to shell out the money for one, though. The first one i hooked up, I had to get on ladder to make sure it was on, it was that quiet.
Something to consider- if you have a builder's model fan, chances are you have a 3" duct also. Most larger CFM fans have a 4" duct opening. So you'll either have to use a 3"-4" adapter, or put in a similar fan with a 3" duct opening.

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