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Old 02-18-2014, 01:12 PM   #1
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Furnace Rattles


I have a Bryant 90i furnace that rattles when it runs. Here are the pertinent details, I can elaborate more as required.
  • If I set the fan to "On", I hear no rattling.
  • As the furnace kicks on, the rattling does not start when the incudcer motor kicks in. It isn't until the blower motor starts that the rattling begins.
  • No idea if this makes sense but sometimes after the blower has run for some time, it kicks into a higher gear and the noise gets louder and then sometimes goes away completely.
  • If I pull out the furnace filter (3M pleated, we have cats and my wife has allergies) the noise stops instantly, even a brand new filter causes the noise.
  • The furnace operates perfectly as best as I can tell and I get no LED error codes.
So why does the fan alone not cause a rattling, the inducer alone does not cause a rattling but combined they do? My best guess is that the blower motor is off balanced when running during a certain frequency range, higher than the fan is set to when running continuous but somewhere in the range of where it runs when the heat comes on. If this is the case, is this something I can diagnose and potentially fix myself? If I used cheaper filters and just changed them more often, would this problem potentially go away or would I just be buying time until it rattled at every frequency?


Last edited by Markus250; 02-18-2014 at 01:15 PM. Reason: More Info
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Old 02-18-2014, 04:40 PM   #2
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Furnace Rattles


probably the cells of the heat exchanger rattling.I've heard it many times.As the heat exchanger heats up, noise gets worse.There are screws around the exterior of the furnace about knee high,that sometimes if you loosen them alittle and then tighten again it helps.If you do it when its making the noise you can narrow it down to a certain area.

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Old 02-18-2014, 05:44 PM   #3
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Furnace Rattles


  • "If I pull out the furnace filter (3M pleated, we have cats and my wife has allergies) the noise stops instantly, even a brand new filter causes the noise." try putting something on top of the filter with a little weight to it or tape it down it could just be the filter rattling in the holder.
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Old 02-18-2014, 10:13 PM   #4
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Furnace Rattles


I got a 3M pleated filter (25x16x1 merv 7 or 8) that worked well for a week or two. I run the fans 24x7 on my Bryant in the heating season. After that, it rattled and made noises. I did not have a replacement, so I went and bought a new filter and it worked well with no noise and replacement filters have subsequently worked (I change monthly because of cats). It might have been a bad filter, since sliding a new one in should not be a problem for a routine 15 second job. - Make sure the filter is not bent or damaged when installing.

Dick
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Old 02-19-2014, 08:23 AM   #5
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Furnace Rattles


check the rounds in the supply fan and check the movement of the squirrel cage on the motor shaft...so that is isn't running up on the fan shroud.if you have no noise when just fan only,but get it with the heat there is something within the heat exchanger bouncing from being heated
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Old 02-19-2014, 08:51 AM   #6
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Furnace Rattles


I will try all of the above suggestions in the next couple days.

I am not familiar with furnaces and am willing (and wanting) to learn on my own what each of these parts looks like and does, however if someone could just let me know which of the listed checks I can and can't do with the gas/electricty on that would be much appreciated.

I also looked up a manual way to change the fan speed while it is running continuous, by quickly cycling it from auto to on (switch twice in under three seconds, right?). Would it be worth cycling through the various speeds to see if I can replicate the noise or was my initial assumption completely off?

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