Practical question regarding ductwork

[ProperVenting]

silencers reduce the sound at the registers only.

Thanks, Chris..so what do I do with 70db motor noise?? That is hell of a lot of noise near bedrooms and with these levels I can wake up all my neighbors. It is friggin loud

[mattt787]

did you start the fan with no ducts on it

[ProperVenting]

did you start the fan with no ducts on it

No, I do not have the fan yet and I am only passing the information I got from tech support. I'm talking about FKD-16 variety

[chrisevansac]

70 db is no louder than the common TRANE condensing unit. Lol

[chrisevansac]

Thanks, Chris..so what do I do with 70db motor noise?? That is hell of a lot of noise near bedrooms and with these levels I can wake up all my neighbors. It is friggin loud

Check out ATC removable insulation

[thermofridge]

Why not just buy one of these?http://www.airscapefans.com/products...se-Fans/Kohilo

[ProperVenting]

Why not just buy one of these?http://www.airscapefans.com/products...se-Fans/Kohilo

Because I do not believe in this solution as it implies that there is 1 (One!!) central location from where it is pulling all air. They are not powerful enuf and what happens when all bedrooms doors are closed. Where it will suck the air from??!!

[ProperVenting]

Check out ATC removable insulation

Hmm..looks really promising and almost exactly what the doctor ordered. Will give them a call on Monday. Thanks a lot.

[beenthere]

Use 26" pipe off of the fan and at least 2 90s to reduce mechanical noise.

[ProperVenting]

Use 26" pipe off of the fan and at least 2 90s to reduce mechanical noise.

With your credentials, I have to take your opinion as a gospel or how it is defined in math as a lemma, however with all due respect I have to ask you this:

1. First of all, are you talking about flex pipe? Does it even exist in this size? Frankly speaking, I thought that going from nominal 16“ to 20” was already overkill so you put completely different prospective on my project and I really appreciate that.
2. Secondly, I assume that 2 90’s will slow down air velocity even more and therefore will further reduce the aerodynamic noise.
3. What size and kind of pipes you suggest to use for each bedroom / bathroom (they are all different sizes). Originally, I thought that for the simplicity sake, I would bring 8” pipe and install one 8” round intake grill regardless of the room size. Am I right about that? Somehow, after I read your opinion, I have a nagging feeling that I am totally wrong.
4. And finally what about the idea of using special sound insulating jackets on a motor?

[beenthere]

I was talking metal pipe. Flex over 20" is not standard in most areas. I'd run flex or sound attenuated duct(last 6 foot) to the individual grilles. Grilles have to be sized for the room they'll be serving and so must the duct be sized for the room.

You could also run duct board as the main trunk line. Duct board has sound absorbing properties. 2 90s in it would still help reduce noise even more.

Small duct work makes for loud air movement noise.

[ProperVenting]

I was talking metal pipe. Flex over 20" is not standard in most areas. I'd run flex or sound attenuated duct(last 6 foot) to the individual grilles. Grilles have to be sized for the room they'll be serving and so must the duct be sized for the room.

You could also run duct board as the main trunk line. Duct board has sound absorbing properties. 2 90s in it would still help reduce noise even more.

Thanks again for the words of professional wisdom. I am wondering if I can step down to 24" round because that is the largest diameter available in flex pipe, everything else above is custom sizes. Also is there a direct equal relationship between sq. area of round duct and rectangular one?

I know that prices are not permitted here but can you at least give me an idea on the difference between all these materials, so I know where to spend most of my time.

[JBM1000]

Having have done some recording studio's, if you have the $ one can create sound isolation by breaking the sine wave of sound and cancelling up to 80% using two methods without losing more than 10% CFM and FPM. at each branch run make a canvas break from round into equivalent duct board with internal 33 degree angled baffling that is up to 1/2 height x 3 into output canvas break again and back into final 5 ft hard pipe or flex at that point. The factoring is outside the box thinking and if sound waves cannot stay in sync with the air at any velocity then "Energy Itself Must Transfer" theory. The duct board and canvas become a heat sink in theory from the fibers of both canvas break and duct board vibrating removing the sound energy.
Take a metal pipe suspended like a wind chime tube and tap it with a metal screwdriver, it rings loudly. now just hold it with your hand and tap it, now it barely has a thud to it. (Do not even ask about related harmonic coupling). Apply that process to your design.