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  1. #1
    Join Date
    Jul 2009
    Posts
    32

    How to Reduce Furnace noise? Please help

    I am in the process of replacing ducts and need a to do something with the noise coming out of the furnace at the same time.

    Right now its all flex duct with sheet metal plenums, Carrier Infinity 96 is mounted vertically, sits on a slab floor.

    At 1500CFM noise is horrible, the whole unit and plenum vibrates, The problem is my office is across the wall, i can feel vibration on this wall with my hand!!! And unit does not even touch the wall, 1" air gap

    The ducts will be replaced with sheet metal ones, maximum supply trunk velocity 700 fpm, branches 600, on the return 600/400 fpm respectively.

    I consider the following solutions:
    1. Add a flexible connection in between the unit and the main trunk
    2. Add anti vibration pads under the unit
    3. Pull the unit another couple inches away from the wall
    4. Add sound dampening foam to the underside of the blower compartment
    5. Add sound absorbing foam to the underside of a 90 degree main trunk elbow to attenuate transmitted noise
    6. sound proof the wall with a low density polyurethane foam.

    Any advice is highly appreciated! I have only one chance to get it done right

  2. #2
    Join Date
    Jan 2008
    Posts
    2,060
    Sounds like the blower is out of balance. Have a professional take a look at it.
    "Hey Lama, hey, how about a little something, you know, for the effort." And he says, "there won't be any money, but when you die, on your deathbed, you will receive total consciousness." So I got that goin' for me, which is nice. - Carl Spackler

  3. #3
    Join Date
    Jul 2009
    Posts
    32
    Quote Originally Posted by 2old2rock View Post
    Sounds like the blower is out of balance. Have a professional take a look at it.
    The unit is only 2 years old, and it was always like that. So I assume its not out of balance out of the factory, unless licensed, "professional" installer hammered on the blades a few times, to make it spin better

    It does not vibrate like its going to take off though, just annoying. And the noise is a low frequency one, coming up the plenum. It sounds exactly as water heater right next to it, but lowder. At slightly lower RPMs noise is almost unnoticeable.

  4. #4
    Join Date
    Dec 2007
    Location
    Cedar Grove, Wi-Sheboygan
    Posts
    1,582
    Could be that the furnace itself is not sitting squarely on the floor or pads whatever it maybe setting on it allowing the furnace to rock when it's running, I have the same furnace and do not have any of those problems your describing. I don't think it's the blower motor myself unless the installer forgot his hammer or something But I bet it's because the furnace is not setting square on the floor.

  5. #5
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,032
    If you physically can see and feel vibrations in the furnace/air handler when it's running then the fan is out of balance for some reason. Nothing you can do to the unit short of fixing the unbalance in the blower itself will make it go away.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  6. #6
    Join Date
    Oct 2006
    Location
    Georgia
    Posts
    48
    Out of balance or has a piece of trash in the blower wheel! It doesn't take much. Also I have been to a few 1-2 yr old systems lately that the hub and blower wheel were not pressed tight from the factory.
    <*}(((-< Good work is not cheap!
    >*}(((-< Cheap work is not good!

  7. #7
    Join Date
    Feb 2004
    Location
    Pacific NW
    Posts
    568
    Have seen both compressors and fans make a LOT of noise because simply one of the mounting bolts is loose, and the rubber 'foot' has fallen out. Even saw this happen on a 3 MW big diesel gen set.

    Have your tech check all mountings, especially the rubber rings on the fan motor. My mom lives 2000 miles away, she finally got aggravated, and called a service company. The tech could not find the low rumble on her 20 (edit - actually 55 YO next year!) YO furnace, suggested a new furnace. On a scheduled visit to help replace her furnace, found that all that was wrong was the rubber rings on the fan motor had detached over the years, new motor rings and good as new.

    BTW, the early 1950's Sears gas furnaces had a relatively thick stainless heat exchanger, over 55 YO and that thing looked better than some 5 YO parts I've seen. Left it in place, just a new motor. (BTW2, pop had died 3 years before, he already had known what was wrong, just never fixed it - there was a new motor in a box behind the furnace!!)
    Last edited by junkhound; 07-28-2009 at 11:02 PM. Reason: numerical error

  8. #8
    Join Date
    Jul 2009
    Posts
    32
    Quote Originally Posted by firecontrol View Post
    If you physically can see and feel vibrations in the furnace/air handler when it's running then the fan is out of balance for some reason.
    So I should feel zero vibration if I press my hand against the unit or duct? even at the highest RPM/CFM?

    Well, if there are some issues with fan mounting/balancing it needs to be fixed. I guess my question was more in a long run, what measures should be implemented to prevent any noise/vibration transmitting?

    Should I add a flexible connector between the unit and supply duct? Is it worth it? What about sound dampening foam? I want to make it as quiet as possible and need to decide before the new ducts go in place.

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