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  1. #1
    Join Date
    May 2004
    Posts
    607

    sound attenuation ideas.

    Ok I just installed a furnace which is in a closet and the return air can is under the unit. Super tight on space.

    They had a 100,000 btu furnace, but load calc came out a lot less as they upgrade windows and insulation. I installed a 60K 96% variable speed furnace. 2.5 tons cooling

    They are complaining the new furnace makes too much air noise. I knew this was going to be an issue and told them new furnaces blow a lot more air than 30 year old furnaces.
    The issue is the return air is right under the furnace and nothing to stop the noise. Plus hardwood floors. The return can is bare sheet metal.

    I can add some insulation to the can, but bubble wrap or fiberglass might not be the best. Maybe something else?

    Has anybody tried adding sheet metal in side the can to reflect the noise?

    This looks cool, but its only found in the UK, class A fire rated too.


    Some fancy stuff

    Last edited by r-290; 06-27-2014 at 02:37 PM.

  2. #2
    Join Date
    Dec 2005
    Location
    Cleveland, OH
    Posts
    2,773
    I've actually lined a noisy return with acoustical ceiling tile once. Oddly enough, worked great.
    Good? Bad? I'm the guy with the gun.

  3. #3
    Join Date
    Feb 2014
    Location
    Statesville NorthCarolina
    Posts
    74
    I've used duct board to line return cabinet, and it works well

  4. #4
    Join Date
    Apr 2007
    Location
    Tucson, Arizona
    Posts
    329
    We actually have an option for a "quiet package" as an add on to most systems. Basically creating a few baffles in the return to stop the sound travel line of sight, picture a vehicle muffler cut out that you've seen and use the duct board to create in inside the return plenum, works every time. Good luck

    I installed special sound attenuators in a music school before, they were store bought duct sections basically with perforated metal and rigid liner inside, those were trick, and silent.
    There are two ways to do things, Right and Again.

  5. #5
    Join Date
    Feb 2014
    Location
    LA CA
    Posts
    18
    Quote Originally Posted by r-290 View Post
    Ok I just installed a furnace which is in a closet and the return air can is under the unit. Super tight on space.

    They had a 100,000 btu furnace, but load calc came out a lot less as they upgrade windows and insulation. I installed a 60K 96% variable speed furnace. 2.5 tons cooling

    They are complaining the new furnace makes too much air noise. I knew this was going to be an issue and told them new furnaces blow a lot more air than 30 year old furnaces.
    The issue is the return air is right under the furnace and nothing to stop the noise. Plus hardwood floors. The return can is bare sheet metal.

    I can add some insulation to the can, but bubble wrap or fiberglass might not be the best. Maybe something else?

    Has anybody tried adding sheet metal in side the can to reflect the noise?

    This looks cool, but its only found in the UK, class A fire rated too.


    Some fancy stuff

    look at this https://www.parts-express.com/acoust...x-12---260-510
    maybe it will work for you.

  6. #6
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,609
    I have a late friend who used ceiling tiles, barely hear a hum.

  7. #7
    Join Date
    Oct 2002
    Posts
    1,394
    Duct liner is designed to attenuate noise. Must not contribute to fire or mold growth.

    Probably, no noisier then last system, just window upgrade made house too quiet.

  8. #8
    Join Date
    Aug 2008
    Location
    San Clemente, CA
    Posts
    1,243
    This is what we do when the furnace is on a platform and the return air chamber and grill is right below. Also you want to check that the return air grill is sized large enough. The bar type grill is better than a stamped and if it is undersized consider a 1/2" cube type grill so it knifes through the air without noise or much restriction. I made these two documents to illustrate.



    Inventor/Manufacturer:
    KoppLift™ Hand Truck Lifting Bar
    http://www.amazon.com/shops/JohnGKoppLLC
    Video
    http://youtu.be/FsSViwAEz7A

  9. #9
    Join Date
    May 2004
    Posts
    607
    I'm going to build something like what JKopp posted. Duct liner is not helping very much

  10. #10
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,791
    A 60,000 BTU 96% at a 50°F temp rise, and a 100,000 BTU 80% at a 70°F temp rise. Move close to the same amount of air. 1067 for the 60, and 1058 for the 100. Of course, they could have had an 80° rise, which would have only been 926CFM. 926 on the 60,000 would be a 57° rise.

    Did you install a new return grille?
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  11. #11
    Join Date
    May 2004
    Posts
    607
    I did not install a new grill. The one they had looked brand new.. something like this.



    Edit... I will see if I can get some real pic's

  12. #12
    Join Date
    Apr 2007
    Location
    Tucson, Arizona
    Posts
    329
    The stamp face grille is the most restrictive and loudest, followed by the fixed bar, quietest would be the egg crate style, looks like the 1/2" grid used in commercial lighting.
    There are two ways to do things, Right and Again.

  13. #13
    Join Date
    Aug 2008
    Location
    San Clemente, CA
    Posts
    1,243
    X2

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