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  1. #1

    Rooftop curb noise and vibration

    Hello,

    I recently had two new trane RTUs installed. I went with curbs and down draft install instead of the original design of stands with side draft attached to a 90 elbow.
    I now have a constant vibration that i can hear through the entire house. 90 feet away in the laundry room i can still hear the unit over the bedrooms.
    The contractor has been back to look at it an has no solution. I feel the new curb is touching the existing metal from the original rooftop flashing and making the sound??

    Does anyone have advise or personal experience with curbs vs stands?
    Should I have felt or some membrane between the curb and roof?
    Should i have sound deadening material in the partition of the curb that is unused.
    I do not have much faith in the contractor, They had all of the right answers before the install and now only point the finger to someone or something else.

    All help would be greatly appreciated.

    Chris

  2. #2
    Join Date
    Dec 2006
    Location
    Litchfield,Il
    Posts
    565
    Chris - It sounds like its not secured to the curb or metal to metal vibrations. There should be some type of vibration dampeners for your unit.
    If your not getting the results you desire then change. People change from either desperation or inspiration.

  3. #3
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    2nd opinion needed.

    Could be as simple as a blower over sized/sped up to the point of cavitation causing the noise?

    Cant see via the web

  4. #4

    fan speed

    I do not feel it is the air flow, the unit is already lowered 50 cfm per ton by use of an enhanced start feature. The unit make the noise when the fan is running at 50% in the start up cycle.
    My hunch is that it is the metal of the existing roof flange touching the new curb or the curb in general magnifies the vibration like a tin can held to a wall to listen.

  5. #5
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Curb installs are way to many for all to request a stand mount due to noise or any other issue.

    Generally speaking there is nothing more them 1/4 foam tape installed between the 2 surfaces.

    Somebody is missing something obvious.

    Just my 2 cents

  6. #6
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190

    Time to call the manufacturer?

    A second opinion from the manufacturer or their local distributor might be a good way to go.
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  7. #7
    I did speak to the manufacturer rep and I was told the curbs can be louder because of the flange directly on the felt paper and not on top of multiple layers of shingles. Also that the downshot can add to some noise. A second contractor has looked at the situation and also confirms that the downshot and short return and supply ducts can enhance noise. When i spoke to the county inspector he also said curbs are often louder than stands.
    It is more the acoustics than overall noise. I can hear it better 50 feet away than under it. The fan noise lessens as i move away but the vibration hum is constant. I think my entire attic is now a speaker?
    I Think I will pay to reinstall back to a stand??

    Thank you,
    Chris

  8. #8
    Join Date
    Jan 2011
    Location
    Ward, Arkansas, United States
    Posts
    811
    Probably need to look at decoupling the noise in the duct work. Just a quick googling...

    http://www.acousticalsurfaces.com/hv...silen.htm?d=26
    "Gentlemen. You can't fight in here. This is the War Room!"-Dr. Strangelove (1964)

  9. #9
    Join Date
    May 2007
    Location
    Dry as a bone Tucson
    Posts
    4,207

    Resi down shot curbs

    What to look for

    1. Is the bottom of the unit touching the edge of the curb? You should be able to have your finger tips fit into the space between the unit and curb, if not then the vibration of the unit can transfer to the curb.

    2. Is there a gasket between the bottom of the curb and unit?

    3. Is there a flex connector between the unit duct opening and house duct work?

    4. Did your installers use hard duct or flex between the unit and house duct? Flex is a better sound and vibration absorber. A flex with a 90 degree turn in it will eliminate most noise's.

    5. Are the electrical and gas connections too the unit hard or flexible?

    6. Is your duct work small and the high static making the blower work too hard?

    just a few things to look at.
    Some Talk, Some Do
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  10. #10
    Join Date
    Apr 2010
    Location
    southern california
    Posts
    535
    Chris, What do you mean by the new curb touching original roof flashing. Do you have a picture of installation. Curbs sometimes cannot span the roofing rafters correctly to distribute the weight. Sounds likes this is a slope roof deck. A carpenter may be needed to solidify structure from beneath if possible. This will deaden sound transmission. Noise transmission thru ductwork is very common as well. Insulating the interior of the curb also is a very effective way to reduce sound.

  11. #11
    I do not have a picture, the units are in place and covering this flange.
    The original install was a side shot into a flex connector and then a 90 elbow. The installer removed the 90 and placed the curb over the existing supply and return that was protruding through the roof. The flashing of the curb is sitting on the original flashing from this duct. The installers then used duct board and mastic to seal the two together prior to setting the unit. I asked about sound deadening material for the portion of the curb that is not in use and I was told it was unnecessary. I guess they were wrong because i feel that is were the noise emanates from.

    Next week i will lift the unit, inspect and reinstall either the curb with better sound absorption or use a stand.

    Thank you to everyone for the help,
    Chris

  12. #12
    Join Date
    Feb 2007
    Location
    Las Vegas,NV
    Posts
    744
    Seems like everyone nowadays is quick to jump on curbs and downshot for residential.
    If the elbow would have been left up there, then all the contractor would have had to do is change the stand and maybe have a small transition to attach the new unit to the existing elbow.
    Now when these units need to be replaced, chances are the new unit will not adapt to that curb and it will be a nightmare changing that whole mess out.
    Chances are, the contractor used one of those cheap adjustable roof curbs and set the unit directly on top of it without anything to absorb the vibration.

  13. #13
    Join Date
    Apr 2010
    Location
    southern california
    Posts
    535
    Chris, Was this changeout permitted, and did it pass inspection.

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