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Charles G
duct air turbulence noise

I have installed ultra-quiet bathroom exhaust fans. The fans are remarkably quiet but noise from air turbulence in the duct work negates the fan's low-noise advantage. I'm using 6" insulated flex duct with 4' of straight run before the first bend. The total run is about 12' to the roof. No sharp bends in the duct. I've lined the 4' straight section with 6" galvanized duct to provide a smooth interior to that section of duct before the air hits the accordion like interior in the rest of the duct. This didn't provide much improvement. Does anyone make quiet, insulated ducting?

canuk
Re: duct air turbulence noise

I find the flex duct is a poor choice since the ribs create restrictions and in cases like yours noise. You're better off using rigid metal ducting all the way with insulated pipe wrap over top.

Re: duct air turbulence noise

I have a detailed discussion of vent pipes for hoods on my blog.
http://kitchen-exchange.blogspot.com/2006/09/hoods-noise-and-venting-q.html
The same applies for any air vent pipe installation.
Your choice of flex duct pipe is always wrong.
I can't think of any installation where it would perform better than galvanized sheet metal ductwork.
And there are some, vent hood and dryer, where flex can pose a fire hazard.
You should replace it with galvanized sheet metal, tape the seams and strap every section down.
Then pack fiberglass insulation around the ductwork to dampen vibration.
I think you'll be much happier with the results.

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