Silencing air through duct work

I saw a demo of a ductwork system that uses fiberglass lining in the duct. Dramatic difference, basically a big glass-pack muffler. I wouldn't use it for a cold air return because I'm not sure the dusty unfiltered air wouldn't just saturate it with fuzz, but on a forced air "source" like a vent fan, it may be just the thing.

I can't dredge up a vendor name from my rusty memory at this time but maybe someone here knows it.

Dave Hinz

typically 6" is used for >200 cfm, 4" for 50 -80 cfm, that's why it's noisy, you could try this

ALL the duct work in the buildings I've worked in has this lining in it. And yes it's almost completely silent. Add the "white noise" speaker system they put in big office buildings, and you'll never notice any noise.

I wonder if you just replaced the last few feet of the duct at the end of each branching with this lined duct, if that would do it ?

Do ya *really* need 300 cfm? If not, slow it down a bunch and the noise will probably go away. Ken.

On Mon, 07 Aug 2006 21:41:34 GMT, Ken Sterling (Ken Sterling) wrote: (someone else wrote:)

Ken, I can't help but think - if the guy thinks he needs 300CFM of ventilation in the bathroom, I really, really don't need all the details.

Thanks guys, I will check with a local duct company to see if they carry this type of ductwork. Only problem is that it is all behing drywall now but if it will help I will cut it out and replace it.

If as you say the noise you hear is not a component of the fan/motor assembly, then noise absorbent ducting together with several abrupt bends in the duct is not the solution. And the noise you hear is created by the speed of the air exiting your register or vent. As others have suggested you may want to reduce the amount of air delivered per minute or go to a more open register or even several. Basically the area of your register produces to high a velocity for the air to pass silently, or silently enough.

cheers T.Alan

Reduce the air velocity by increasing the duct size.

Ken.

Something else you could try would be to splice in a "T" in the ceiling above, and put a butterfly damper plate in it, to adjust the amount of air drawn from the bathroom.... the "excess" air could be drawn in from the attic space. Ken.

You could just go to Home Depot and buy the quietest bath fan. I installed one 6 months ago in a friends house and it's amazingly quiet. Of course I realise that defeats the whole purpose of this group. Karl

mark wrote:

You sure will. You just turned the faraday cage of the computer case into something RF transparent. So more interference in the house but it's quieter in the audio frequencies.

Computers are easy enough to make quiet - they have whisper fans with great airflow and features which make them quiet, especially on an idle system. Worth looking into.

Or do as Junior did, and line 90% or the case with the sound deadening material used when installing high end auto stereo systems - basically a lead composite sheet coated with contact PSA. Gerry :-)} London, Canada

Read the bathroom fan FAQ