Its a duct


Old 04-06-15, 06:32 PM
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Join Date: Jul 2008
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Its a duct

Have a large addition going in (3700 + to heat/cool) and our permit has us with 2ea 3 ton units.

I have talked to several professional companies and have divergent opinions regarding ducts.

I specify that I want a quiet system where you don't hear much air rushing through the registers.

One suggests using "ductboard" plenums and "flexduct" branching.

Another suggests using "flexduct" excusively and branching the first drops "up the plenum" and then doubling back when close to the air handlers.

Since the ductboard quote is about 33% more than solely flexduct, I don't mind paying more for a superior solution but cheap enough to not want to waste money.

Will sure appreciate hearing some opinions on this subject......


flbuild, central florida.
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Old 04-06-15, 10:50 PM
Join Date: Mar 2006
Location: Wet side of Washington state.
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It may take the Airman (our resident expert in this area) a few days to respond but I can tell you that flexible duct is the cheap method. Further, it is less the duct material and more the velocity of the air through the duct AND the terminal register, that creates noise. Lower velocity means bigger ducts or more of them.
Old 04-07-15, 05:59 AM
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Join Date: Dec 2005
Location: VA
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Oh wow Furd just put a lot of faith in me!! I will try and help you out but I might just give you info to make your own educated decision.

A system of just flex duct (spider system) will be the cheapest! It will most likely be the hardest to have even temps from room to room. IMO this is a system that should not be used.

Duct board has been used for many years and it can work well. As I understand it Duct board is used a lot in Florida. Two issues I have with Duct board. 1: They will grow mold easily. They do in VA so I know FL will be game on for mold growth. 2: The fibers will become friable after some time. It might be as long as 20 years put they will always break down. Fiberglass floating in the air is not my idea of a good time.

Metal duct will be the most expensive!! It will not break down! It does not support mold growth. It will have to be sealed and insulated. But it will be by far the best!!!!

All can be quiet but they will have to be designed correctly. My choice would be for metal. My father used to always say when in Rome do as the Romans do. So maybe with that logic the duct board is the way to go. Id just inspect it once a year for mold growth.

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