Residential bath fan soffit terminations

[nizak]

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]

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]

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.