I have a vibraton in furnace only when flame is lit. Blower motor seems fine. Is this vibration normal? Recently replaced inducer motor. Heat exchanger has been replaced once. Does not appear to be any cracks or orange flame. Does not do this when A/C runs only when furnace runs. Any ideas?

  • It's not extreme but am concerned exchanger going or will go due to vibration. Guess it's not normal but is it something to be concerned about? Read speed during heat is slower than when A/C runs. Does not seem to do it all the time but often enough. – Tim Nov 2 '14 at 1:09
  • I'd suspect the new inducer motor if this sound begins to occur just before ignition; before the HSI gets hot. At what point in the system start up does this begin? – Mazura Nov 2 '14 at 2:32
  • No, after the flame lights and it warms. Then blower comes on. You hear it thru duct work before blower motor comes on. Is it just natural sound of it heating, more like a humm. Farely loud but not extreme. Loud enough that a homeowner would notice it. What is HSI? – Tim Nov 2 '14 at 15:29
  • Been told possibly limit switch or gas valve? – Tim Nov 2 '14 at 17:59
  • Thank-you, i tightened down clamps that led from inducer motor to plastic pipe. Also put a little piece of insulation at top where pipe was resting on housing of furnace. Seems to have helped, however I ran it again and first cycle got the vibration,(this time it started after blower motor came on, has not in past, NOT AS BAD). Still goes away when flame out and second time I ran it no vibration...is it possible its blower motor, sounds so smooth. Inducer motor less than year old. – Tim Nov 2 '14 at 19:20

I'd suspect the new inducer (exhaust) motor if this sound begins to occur just before ignition; before the HSI ( hot surface ignitor) gets hot. A gas flame makes more of a roar than a hum. I've had less than stellar inducer motors in the past, with questionable bearings making it sound like rum-rum-rum-rum...

I've also had duct work vibrate at the unit; go around putting pressure on things until the sound changes. I still believe the sound is caused by the inducer; though it's not necessarily the source of the sound.

Take the furnace's top-section of the faceplate off, and try grabbing stuff; beware the 120v wiring. Tighten down the clamps that lead from inducer motor to the plastic pipe. Also try putting little pieces of insulation where piping might be resting on things.

It's not unheard of that replacement parts be less than spectacular. Encountering this exact problem, I've lived with a (now a little less) noisy replacement inducer for 10 years now.

  • So Mazura thanks again. What your saying in that last paragraph is it may just end up being that way? Not necessarily bad but may have to live with it? Unit at least 12 years old, only started last year. HVAC guy coming out but really don't want to hear any bs. Thank you again, very helpful! – Tim Nov 2 '14 at 23:58
  • Not sure my post went thru, so you are saying by your last paragraph that it may not be bad just have to live with it? HVAC guy coming out but don't want to hear any bs. You have been very helpful, thank you. – Tim Nov 3 '14 at 0:02
  • Living with it is your choice; HVAC guy is going to ask 'what you want me to do about it, replace it or leave?' – Mazura Nov 3 '14 at 3:11
  • Lastly, the coil part of motor will get warm, can keep my hand on it. My buddy and I put it in, so easy. Is there anything we could have missed? Pipe that goes to outside wall, could it be restricted in anyway? – Tim Nov 3 '14 at 9:41
  • Check this out, took inducer motor off and reset it. First cycle quiet as can be, second time vibration back...go figure. Ready for new unit. – Tim Nov 4 '14 at 23:11

I would first fully inspect the exhaust for obstructions.

It is quite possible that in the process of combustion, pressure is building inside the heat exchanger, and then having difficulty moving through the appliance to eventually exhaust.

The inducer is designed to help overcome this.

Basically, what happens is that the combustion pressure overcomes the ability of the fan. Some "slippage" over the fan tips will occur and the fan catches up. Left alone, this can cause a noticeable rumble that is methodical.

Spelling may be incorrect, but it is called the heimheld effect (I am a combustion guy).

Look for obstructions in the flue...excessive flue lengths.

Call the OEM tech line, or search boards "specifically" for your model. Tech lines are VERY helpful, if you accurately describe the issue.

As someone not in the industry, you may not get to them easily...but being polite will open a lot of doors.

Maybe start with the local sales rep in your area...he will have a guy on speed dial..and you might just remember him when it comes time to replace!

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