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#1
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How to reduce low frequency noise from a gas furnace?
I had a new gas furnace instilled at my house. When the burners come on it makes a very loud rumble, similar to a drum-roll on a timpani. The installing company claims this as normal, and refuses to do anything other than sell me another furnace. While I may buy a different furnace – the 90+ % efficient furnaces are reported as much quieter than most 80% efficient furnaces, I definitely won’t be buying it from the same vendor. I want to investigate to see if the noise can be dampened before spending several thousand more to replace the furnace again. I'm looking for feedback on how reduce or eliminate the noise. The source of the noise is the burners. The noise passes through ducting and comes out of baseboard heat vents. I guess the frequency is somewhere between about 20-70 Hz. The noise can be heard at all the vents at the downstairs area, but not at all upstairs. Note that the furnace is mounted under the downstairs area, in a crawl space. Based on this, one possible solution is to change the installed ducting to use a kind that has sound absorption material. Another possible solution, is to modify the plenum to provide better sound absorption - or something along those lines. It occurred to me to use the plenum or the ducting to create a muffler of sorts, but I don’t know how mufflers are made, or if concept is applicable to a furnace. Any suggestions on how to eliminate the noise without loosing a lot of air flow? TIA |
#2
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You could check and see if any of your ducts are loose and secure them or use a product like this:
http://www.owenscorning.com/comminsul/products.asp?product=289 Good luck.
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Chad 2006 Nissan Pathfinder LE 1998 Acura 3.0 CL OBK#44 "Pleasure in the job puts perfection in the work." - Aristotle (384-322 B.C.) SOLD 1985 300TD - Red Dragon 1986 300SDL - Coda 1991 - 300TE 1995 - E320 1985 300CD - Gladys |
#3
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You have a pulse furnace - my home has two!
Here are some hints: You could build a box around it out of insulation and cardboard - that should help. Isolate the furnace from the house structure - if it is up in the attic or bolted to a floor other than the basement slab, insist that the installer isolate it properly - he should have known better! Make sure the intake and exhaust lines are not tightly attached to the house structure - they vibrate and transmit noise too. Finally, you will still hear the noise no matter what you do. I got used to it pretty quickly and don't mind it at all now.
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1984 300TD |
#4
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Yeah...I thought it was a characteristic sound of gas furnaces...I remember the same in homes that I grew up in.
Here in Texas, the units are in the attic, and with the insulated foil ductwork, the noise is greatly reduced. I'm not sure you can do much with solid ductwork...noise transmittal is guaranteed.
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2009 ML350 (106K) - Family vehicle 2001 CLK430 Cabriolet (80K) - Wife's car 2005 BMW 645CI (138K) - My daily driver 2016 Mustang (32K) - Daughter's car |
#5
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I think you can replace a small section of the duct near the furnace with a flexible piece. Some HVAC guy should chime in with the proper name
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#6
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Not a HVAC guy but this sounds like a good idea
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MBlovr '59 180 Dad's original '59 180 Dad's 2nd one '67 250SE Dad's last one '59 220 SE My first one '62 220SE Coupe second one '89 190E 2.6 5spd third one '06 E350 4matic (sold) '10 E350 4matic |
#7
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Buy some rolls of car audio sound deadening sheets, like Dynamat, and cover your furnace ductwork. Clean the ductwork first and check it for resonance. Cover the spots that vibrate the most.
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Regards Warren Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL ENTER > = (HP RPN) Not part of the in-crowd since 1952. |
#8
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I like that idea about the sound deadening. Dynamat is pretty expensive, I used a similar product that was much cheaper (in my truck)
http://www.b-quiet.com/ |
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John Robbins '05 E320 CDI - 240k '87 300TD - 318k |
#10
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Quote:
This or something similar might be a big part of the solution. I was looking at how mufflers work at this site. http://auto.howstuffworks.com/muffler3.htm It appears that one of the tools they use in muffler design to set up resonant chambers which serve in part to cancel the noise. They also use different metals to absorb some of the noise. Mufflers run under much higher pressure than duct work and I don’t think I can get use of a resonant chamber, but can do something to absorb the low frequency sounds. |
#11
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I'm not sure i know what a pulse furnace is. Can you elaborate?
They say mine has "inshot" burners. These are attributed as the cause of the noise. Quote:
Quote:
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#12
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Quote:
Quote:
There is a kind of ducting which is rigid, but which has dense insulation lining on the inside. It is pricy enough that it will be less cost to just buy a 90% efficient furnace. I’m thinking of replacing the plenum with a bigger one, and using many layers of noise absorbing material as a kind of baffle. The idea is similar to that used in glass pack mufflers. I don’t know if rigid noise absorbing material is going to have better results than soft material. I haven’t found anything that specifies the sound dampening qualities of the material. |
#13
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This is an additional possibility, and another is to get a smaller piece of rigid ducting, but which has with sound absorbing material inside.
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#14
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Quote:
The real problem is when the burners first off and before the fan engages. After the fan engages you can’t hear the drum roll any longer. |
#15
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