Fan hissing in new Ruud - http://www.hvacmechanic.com/ Forums
Original message
| jpinmo
 |  "Fan hissing in new Ruud"
, posted Mon 21 Jul 10:47  
In May I replaced the failing and ancient central heat/air unit in my 1940 era house. The house is well built and the ductwork drew compliments from several of the contractors who bid on the job. I picked a well established contractor who completed a Manual J heat gain/loss calc on the house. Since I plane to live here a long time, I choose a high end heat pump unit (93%) & 15 SEER from RUUD, the UPRL series. The installation went fine and the unit is cooling the house well enough.
But there is this high frequency hissing/static type noise that is still making this unit unsatisfactory. The VS fan is fine on the low setting with no noise, but as the fan comes up to cooling load, heating load or just high fan speed, the hissing that comes from the ducts gets into my ears and won’t go away. The ducts closest to the indoor unit are the loudest and the sound fades the longer the ducts are. The contractor guys have been good to change out the fan, the aux. heat exchanger, and the evap coil, but still the same hissing. They have looked over all the ductwork and don’t find a source of the hissing. The regional distributor calibrated the temp. and air flow and still the hissing is there.
A factory rep came out and looked things over and asked relevant questions of the tech guys and concluded that the sound is coming from turbulence in the new unit. He tells me that all the makers of the high efficiency units use a similar design and that this noise is part of this type of equipment. His idea was to install some flex duct to the short runs to dampen the sound.
I am wondering whether to start over with new equipment from another maker, (but will I still end up with similar hissing?) or to try some of the flex ducting or what about duct liners? Can liner be installed in the existing ducts or not and is the liner safe?
Any informed opinions on this situation would be greatly appreciated. Thank you.
JP
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Replies:
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| Freon
| "Re(1):Fan hissing in new Ruud" , posted Mon 21 Jul 15:27
You need to be sure where this hissing is coming from. My guess is it's high velocity air flow through registers and through the filter.
Try removing all filters and set the fan to high. Still hissing?
Now the harder work. Try removing supply vents and see if that helps. If you hear hissing, is it deeper in the duct system? If so, a possible obstruction or a hard 90 degree elbow that could be replaced by 2@45.
Flex will help if the noise were caused by vibration but will not do anything for high velocity air flow oter than cause a greater pressure drop and slow the air down. Dampers are a better way to slow the air at hissing supplies so it goes to supplies further down the trunk.
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| | jpinmo
| "Re(2):Fan hissing in new Ruud" , posted Mon 21 Jul 21:56
Thanks for the ideas... with the filters removed the hissing is still the same... with the unit partially disconnected from the main supply and air coming out all over the place, the hissing appears to be coming from within the fan, exchanger and coil unit... as far as I can tell the noise is not in the ducts...
Should I go for the equipment change or will a similar unit probably sound the same?
Thanks again.
JP
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| | Freon
| "Re(3):Fan hissing in new Ruud" , posted Tue 22 Jul 10:55
Good work isolating the area of the noise. Until you know the exact cause, you may still have the same problem. I'd call the company back and show them what you have discovered so far. They should be able to find the cause now.
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| | jpinmo
| "Re(4):Fan hissing in new Ruud" , posted Sat 2 Aug 07:07
The hissing noise is coming from the heat exchanger of the gas furnace of the new unit. With the unit off and listening in the duct a light tap on the exterior of the furnace unit leads to a metalic vibration sound that fades away in a couple of seconds. I imagine when the fan is on this vibration is amplified a great deal.
The contractor says nothing can be done to stop this sound in the heat exchanger, it is normal. Is it? They want to start duct modification to damper the sound, I don't plan to go this route. Are there quiet high efficiency furnaces out there?
JP
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