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  1. #14
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,324
    Sound attenuating flex, will be more of a waste of money.
    You got more trouble then it can cover up. Your noise is velocity noise.

    On High Velocity duct systems. You use 3' to absorb the noise.

    Your system is suppose to be a low velocity system.
    Your jaming 2½ tons of air, through a 1¼ ton distribution system.
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  2. #15
    Join Date
    Mar 2006
    Posts
    254
    Actually, 2 tons into whatever you said. ( now 8" duct to major area of concern).

    Ok. Thanks for the tip about not going for the acoustically modified flex duct.
    Most of it I can't even find a USA distributor for it. It's all from the UK or AUS or
    the manufacturer....in China.

    Beenthere...maybe after I get the ducting sized right, I won't have to do any fancy
    lengthening of the duct. I still say that is a mighty short elbow duct length from the plenum to
    my living room vent. You may advise some unique duct working on that.

    Another question if I may. If the sheet metal opening at the wall that now holds the end flex duct to which the register is attached to (now 12"x 6")...do they have to rip that out to put in a 12"x6" metal opening (what you attach the register to) to fit the bigger flex duct?

    If so, I can see how that might get a bit more pricey. Is this so?

    Also, I take it they make a "wall" flex duct end that can still be 12"x6" and fit a bigger flex duct so I don't have to cut into my wall and make a bigger opening than 12"x 6"?

  3. #16
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,006
    Always on a change out or new installation, first things first!

    First,
    a manual J should have been done, & any heat-gain reductions performed, after which you recalculate, so you will know how much CFM is required for each room.

    A 1.5-ton system may even be somewhat oversized for your situation.(?) A 1.5-ton would reduce the needed airflow through the ducts.

    I can't see your stated sf, using two 20" box type fans for air circulation back to the room A/C, I cool & dehumidify perfectly an old 1937 farm home first floor 850-sf plus with a mere half-ton, 6,000-BTUH Window Room A/C.

    One ton split systems are not easy to find but I would bet your home could be retro-ed so a perfectly set-up one ton would cool it.

    Then the duct system needs to be sized to deliver the correct amount of CFM airflow to each room which in your case, would be 500-fpm velocity. Due to the short runs, that could mean two supply registers in the noisy room, & perhaps other rooms.

    Both the supply & Return ducting must be sized correctly for efficient & quiet performance. - udarrell

  4. #17
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,324
    A system has to be looked at as a whole.
    Increasing the size of the duct its self will not help.
    The register box is also too small.
    Remember in your other thread, I said about adding another supply beside that one.
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  5. #18
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    Looking at the pics on your other thread...the slope of the living room ceiling...does it at some point form a knee wall in the attic, say, above where your computer screen shown in one of the pics is?

    Without actually being there, I'd say between your analysis and beenthere's, it's a combination of undersized duct, restrictive supply grill, and close proximity to the supply plenum that in aggregate are causing your noise problem. I mention the knee wall, as if it exists, seems a longer, properly sized duct run, perhaps two, could be run around to that wall and then two supply boots set pointing toward the wall with the vertical blinds covering the window shown in the pic.

    If you want a more modern look you could just poke through the wall with spiral duct and hang a couple of supplies on it.

    Look for a contractor who has training and/or has technicians trained by either the Comfort Institute or the National Comfort Institute, which specializes in air balance training for residential settings.

    As for "dying breed" discussion, the only "dying" that really needs to happen is the "get 'er done" attitude...which certainly is not confined to the HVAC trade. "Get it done correctly" is ultimately more satisfying for both contractor and customer. I think there's plenty of customers willing to pay for a job done correctly...the challenge may be finding someone on the contracting side that has the same approach.

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