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Residential bath fan soffit terminations

Merry Christmas
N

nizak

Senior Member
I recently installed a 150CFM bath fan.
It’s a .8 Sone noise level. I have successfully used this model for a few years with 0 issues.

It requires a 6” duct.

This time the HVAC contractor is someone I’ve never worked with and they did the venting. The fan is considerably noisy and seems to “cycke”as it runs.

It will operate relatively quiet for about 30 seconds ( not as quiet as it should) but will then get louder.

It appears to cycle this way.

The soffit termination appears to be a 4” size.
Could this be the problem?

G.C. Is telling me that the fan is defective.

I’m saying it’s the venting.
 
Seven-Delta-FortyOne

Seven-Delta-FortyOne

Goin’ Down In Flames........
Location
Humboldt
Occupation
EC and GC
You’ll need to get into the attic and inspect it. If they have flexible duct with extra length, and it’s unsecured, it’ll definitely do that, as well as if it was installed in such a way as to allow water to accumulate in the ducting.

I’ve personally seen both situations.

Preferably, hard pipe should be used when it can be for longer runs, and flexible only for attachment to the fan, excess cut off, and ducting secured. Some will say that is overkill, but all of my work is custom and I want “Oh WOW!!” at the end of my projects, not “um OK 🤔”.
 
Seven-Delta-FortyOne

Seven-Delta-FortyOne

Goin’ Down In Flames........
Location
Humboldt
Occupation
EC and GC
And yes, reducing the size at the end can cause noise. If you need to reduce, it’s best to do it at the fan with a 6x4 reducer, rather than at the termination.

And for what it’s worth, with the Panasonic FV0511 series, if you get the 150 CFM with a 6” outlet, and reduce it to a 4”, you reduce your CFM to 110, so you might as well get the 110 version which comes with a 4” outlet.
 
James L

James L

Senior Member
Location
Kansas Cty, Mo, USA
Occupation
Electrician
It's 99% certainly the ducting. Reducing the duct size increases turbulence. Making matters worse is having too many elbows in hard pipe, or having undersized flex laying around.

For a frame of reference, I installed a 130 cfm fan once, which stated either 4- or 6-inch duct. The size was right on the line I guess. I chose 4-inch for ease of installation, and I used a hard 90⁰ elbow attached right on the fan. It was too tight for the 130 cfm, and made all kinds of noise because of the turbulence. I changed that elbow to 6-inch and the noise went away.
 
A

AC\DC

Senior Member
Location
Florence,Oregon,Lane
Occupation
EC
I would not crawl around swap gut out with a new one. Bill out gc when it still makes the sound and tell him to get his crappy hvac guy to fix it. I don’t work with to many gc as you can tell I hate them
 
N

nizak

Senior Member
I told GC that the HVAC contractor needs to take a trip up in the attic and inspect the ducting.

It’s located at the opposite end of the house from the attic access and you need to cross a vaulted ceiling as well.

He hired a “less expensive “ HVAC guy for this job.
My guess is he got just what he paid for.
 
N

nizak

Senior Member
fishin' electrician said:
Standard framing only allows a 3" duct to exit into the soffit and that's a lousy place to dump warm, moist air considering most soffits allow air intake.
Click to expand...
I did physically see 6” ducting installed by HVAC. It was just laying in the attic space at that time.

I don’t know the duct condition after the blown in insulation was installed or how it exited the attic space and into the soffit.

I can physically feel the air coming out of the soffit termination but feel there’s some type of obstruction somewhere.
 
Seven-Delta-FortyOne

Seven-Delta-FortyOne

Goin’ Down In Flames........
Location
Humboldt
Occupation
EC and GC
AC\DC said:
I would not crawl around swap gut out with a new one. Bill out gc when it still makes the sound and tell him to get his crappy hvac guy to fix it. I don’t work with to many gc as you can tell I hate them
Click to expand...



There's still a few good ones out there. (y)

The subs that work for me, regularly call me asking if I have anything in the pipeline for them.

But, I never have, and never will do, "pay when paid" contracts, I think they are unethical, I pay as soon as they are done, I don't call them until I've personally walked the site and made absolutely sure its ready for them, if they do waste a day because something wasn't right I pay for the extra time, I try to make things as set up for them as possible, and I have clear scopes of work for who is doing what, and don't try to tag on extra stuff because of my poor planning.

Just some of the little things I try to do, and treat the subs like team members instead of like a slave I'm squeezing to death.

But I've heard plenty of horror stories about GC's. Blows my mind how some of these rear-end hats are even in business.
 
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