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    Eric D's Avatar
    Eric D Posts: 98, Reputation: 4
    Junior Member
    		  
    #1

    Jan 10, 2008, 07:05 PM
    Fan / Air Noise Heard From Vents - to Reduce?
    I'm looking for ways to reduce fan noise that travels through the supply trunk to each of the outlet vents. I've reduced the fan speed and this helped a little. What have you use that work?
    T-Top's Avatar
    T-Top Posts: 1,871, Reputation: 100
    Ultra Member
    		  
    #2

    Jan 10, 2008, 07:26 PM
    Is It noise from the fan motor or a restricted air flow noise? If it's a air flow noise at the registers you will need to add a supply run if lowering the blower speed did not work. If you have a 3 ton system it needs to move X amount of cfm to work(rule of thumb 400 cfm per ton). It sounds like your duct work is under sized for this size of system. Supply duct and or return duct.
    Eric D's Avatar
    Eric D Posts: 98, Reputation: 4
    Junior Member
    		  
    #3

    Jan 10, 2008, 08:02 PM
    I can't tell the difference from fan or air flow noise. I can tell you that the fan doesn't have bearing or out of balance type noise. Chances are it is air flow noise. The system is geothermal system, if that matters and it is a 3.5 ton. If I remember right, the fan on the highest speed is rated at 1750 cfm. Both the supply and return trunks are 8x24 inch.

    I was wondering if was some type of sound absorber that could be placed in the ductwork?

    T-Top, thanks for your input!
    letmetellu's Avatar
    letmetellu Posts: 3,151, Reputation: 317
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    #4

    Jan 10, 2008, 08:37 PM
    There is a fiber board that you can glue in the trunk lines as far as you can reach, it will deaden the sound to some extent. But if your furnace or air handler is in the attic space I can tell you that they are just more noisy that one in a closet on the ground floor.
    You can also line the inside of your air handler with this fiber board, which is just a stiff fiberglass board about one inch thick.
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #5

    Jan 10, 2008, 08:40 PM
    Many years ago I used to make a plywood panel and cover it with carpet. I used to angel it 70 degrees to the square of the return duct near the blower. It would chop the air noise right out of the system. I no longer have a drawing and I am not about to do another one but if sized correctly it will not effect the return air CFM enough to cause a problem. Do a Google you might be interested in what you might find in regards to duct noise elimination.
    Frdbrkl's Avatar
    Frdbrkl Posts: 94, Reputation: 7
    Junior Member
    		  
    #6

    Jan 12, 2008, 07:33 AM
    Hmmmm... 8x24 inch plenum and return. Sounds like the ducting is undersized for a 3 1/2 ton system. Just a thought. HVAC1000, Missouribound, am I off base here?

    And remember, reducing the fan speed may have mechanical consequences-this should be done only with cross checks (temp rise, pressures, etc) to prevent equipment damage.
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