Noise Issue - Inducer Question


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Old 11-04-14, 11:28 AM
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Noise Issue - Inducer Question

im trying to track down a periodic buzzing noise I am getting when my heat is running. I cant even say for certainty if its originates from the furnace itself, the ducting or something unrelated.

It appears to happen in only one room. I do not hear the noise when standing in front of the furnace. The buzzing starts after the burners are lit and the fan is running. It only last for a few minutes and stops before the gas valve shuts off.

I could go on and on telling you what I have checked but for the sake of brevity.... I wanted to rule out my inducer fan as a possible culprit.


I have a single stage condensing furnace. It uses a fasco 93W13 inducer.

My question.... is that a single stage, single speed inducer?


I guess I will throw this out there too... if a noise was generated by a mechanical issue with the furnace itself and was amplified thru the duct work... would I likely hear this noise standing in front of the furnace as well?? Is it possible to hear a failing motor bearing or a buzzing transformer beings transmitted upstairs from a furnace but yet wouldn't be able to detect it standing in front of the furnace itself?
 
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Old 11-04-14, 04:55 PM
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Some single stage furnaces actually have a two speed inducer. They will start their pre-purge on high then drop back to low during the firing cycle.
Noises can be a bear to track down especially if they come & go and can be heard in only one room.
 
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Old 11-04-14, 09:53 PM
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That is a single speed inducer motor and I highly doubt it's the cause of your noise.

The only thing I can think of is the heat exchanger is resonating. I've heard it standing at a furnace and I've heard it as a repetitive vibration in other rooms. It's sounds like a cross between a vibration and a harmonic rumble.
 
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Old 11-05-14, 04:41 AM
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That is a single speed inducer motor and I highly doubt it's the cause of your noise
Thanks, I ruled that out too since the noise starts after the inducer has been running for a few moments and it stops before the inducer stops. I asked about the variable speed thinking maybe it only made the noise on one of the speeds or something.

It's sounds like a cross between a vibration and a harmonic rumble.
Throw in some 60 cycle hum and you nailed the description. What driving me mad is that its not a consistent sound, it does not start and stop with the furnace. It starts at some point during the heating cycle and stops before the furnace shuts off. It also does not happen each and every time the furnace cycles.

Standing in front of the furnace with the cover off or on there is no evidence of the same noise in the cabinet. In fact I cannot hear the noise at all in the furnace room itself. Its only evident about 20' away, on the other side of plywood.

Do you think its safe to rule out a mechanical issue with the furnace itself then? And focus my hunting on the ductwork in just the vicinity I hear the noise?


The next step, beside pulling my hair out, is drastic. The supply and return trunks that run thru the center of the house (this is also the vicinity I hear the noise in) have been framed and covered when someone finished the basement long ago. To be able to get at them I would have to remove the damn plywood ceiling. I am not sure if I should go to that extent though.
 

Last edited by rards; 11-05-14 at 05:03 AM.
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Old 11-05-14, 05:44 AM
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I mentioned buzz and 60 cycle hum. Grasping at straws here but if it was a faulty transformer, do you think I would be hearing only during a portion of a heat call or would a faulty transformer (or one that isn't quite tight) hum at all times?

And the main question, (since I know diagnosis of this over the internet wont bear much fruit), if I don't hear it in the cabinet while in front of the furnace is it safe to rule out a mechanical problem in the furnace itself?
 
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Old 11-05-14, 01:46 PM
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beer and pizza for anyone who can help me solve this.

Still hunting:

I found a 3/4" hole drilled thru a joist that makes up part of the return... inside you can see where the trunk was cut for that inlet to the return. There is sheet metal cut and folded and dangling in the return.

Do you think that quarter size hole in the return could cause a intermittent noise issues?

Sealed the hole temporary with tape to see if that is an issue.
 
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Old 11-05-14, 02:53 PM
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I'm going with TJmax's theory of heat exchanger resonation. Does it happen only after the furnace has been off for at least X minutes? Does it normally last about the same amount of time?
 
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Old 11-06-14, 12:27 PM
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Grady - There is no rhyme or reason in regards to how long its been off. It does normally last about the same time, 2 minutes in the middle of a heat cycle starting and stopping while everything is on (ie gas, blower, inducer etc)

Its can be heard in the middle of the ducting system about 15' away from the furnace. Theres a partition between that room and another where the furnace is located. The closer you get to the furnace it is quiet. There is only normal operating sounds when in the same room as the furnace and nothing is detected with the cover off the furnace.

Ive tried many things. I cannot afford to hire someone to come over and try many of the same things I tried. Just to have someone here trying to recreate and wait for the sound would take HOURS! Even asking these questions here are a waste of time..... the fact that its intermittent is also frustrating.

I don't know how to proceed, Ive exhausted most of the things I can check short of tearing apart a ceiling to get at the main trunk.
 
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Old 11-07-14, 03:43 PM
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I doubt it will help but try taking the register(s) in the effected room. I have seen cases where the fins would actually make noise. I understand your frustration because I've chased intermittent problems, including noises, many times.
 
 

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