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  1. #1

    Duct details in new construction.

    First of all, thanks to everyone who helped me out awhile back with picking out a good HVAC contractor. Your advice helped me weed out a bad installer and hook up with a good one. Now I'm helping out my brother in law who will be building his first home in Buffalo NY. Where he is building, there is already a builder attached to the site.

    I was looking at the HVAC system that my brother in law's builder had installed in a home next to his (where his will be built):

    I noticed that the return air passeges were not lined, they were bare studs and drywall. It's my understanding that returns should be fully lined - am I wrong?

    I also noticed that the tin in some floor returns was not sealed, so that air would be pulled from the basement instead of the room where the return is pulling from. You could look up through gaps into the room above. Is this sloppy work that is not acceptable?

    The duct sealent applied to the joins in the metal duct also seemed very thin - neat but very thin, like one coat of latex thin. It didn't appear to be enough material to seal the ribbed metal that slipped into the next tube. If you were eyeballing someones sealing work, how would you judge it's likely effectiveness?

    Lastly: He will be having part of his basement finished. He is getting a 9' deep basement instead of the standard 8'. Alot of the supply duct goes over that finished space, and there will be branches off those main lines to supply this finished basement area. What should he ask for from his HVAC contractor to ensure that a loud boisterous poker game in the basement isn't piped into every room in the house?

    Thanks for any advice you can offer!

  2. #2
    I see there are duct "silencers" on the market, but they look to be more for fan noise. In other conversations I've seen that a line of flex duct may significantly reduce the sound before it enters into a big trunk line.

  3. #3
    Doing some searching around, I've seen that the bare studwall plenum can be OK, as long as it is sealed. One method I saw was flushfitting drywall between the cavites and sealing the seams with mastic and mesh tape. I would think masic on the studs with a layer of sheetmetal would be easier.

  4. #4
    Join Date
    Aug 2002
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    Office and warehouse in both Crystal River & New Port Richey ,FL
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    Seal the stud spaces,if they must be used.

    Seoarate return duct(s) for the basement ,not just a gille stuck in the return trunk going to the floor above will help reduce noise transmission.

  5. #5
    How would you seal the returns if they were in the stud bay like that - or would you do something else entirely?

    A grill stuck into the bottom of a supply trunk is exactly what I saw in that house. What you're saying is to have a seperate branch just for the basement supply - that should alleviate most of the noise issues. Makes sense to me.

  6. #6
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    Quote Originally Posted by xxpaulcpxx View Post
    How would you seal the returns if they were in the stud bay like that - or would you do something else entirely?

    A grill stuck into the bottom of a supply trunk is exactly what I saw in that house. What you're saying is to have a seperate branch just for the basement supply - that should alleviate most of the noise issues. Makes sense to me.

    I'd wouldn't use the stud space,mastic the wood joints if they do,plus mastic the panning to the wood.

    Two 90° elbows in the return duct will stop most noise transmission,two 90's also means you need larger duct ,due to the restruction of the turns.

    "Quietturn" ,turning vanes in elbows in elbows will reduce noise transmission even more,plus they reduce the restriction in air flow,of the elbow.

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