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Old 01-07-2009, 04:21 PM   #1
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Acceptable Blower Vibration


This morning the blower wheel in my York furnace came loose, creating a lot of vibration and loud noise that could be heard throughout the house. I removed the blower assembly, carefully repositioned the blower wheel (it had rotated about 15 degrees from alignment with the flats on the motor shaft), tightened the set screws, and reinstalled the blower assembly. It now runs quietly, and there's no perceived vibration in the duct work or external furnace housing, but the blower assembly itself and the control unit mounted on it vibrate noticeably.

This is the first time I've worked on this (or any other) furnace, as we've moved here recently and all previous homes I've owned had oil-fired hot water systems, so I don't have a reference point to what acceptable vibration is. I do, however, have experience with presumably higher quality blowers used in industrial applications, and they generally don't vibrate this much unless the motor bearings are shot or the blower wheel is damaged/out of balance.

Searching this site, it seems a little vibration is common, so perhaps I shouldn't expect as smooth operation as I'm familiar with on industrial gear. Does anyone with more experience recommend changing the blower wheel (it's nearly a third the price of a new motor), or is a little vibration to be expected?

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Old 01-07-2009, 05:50 PM   #2
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Acceptable Blower Vibration


the test for a vibration is as simple as removing the blower squirrel,and rolling it away from yourself on a carpeted floor,and see if it wavers on the outer edges.if there is any buildup of dirt in the squirrels rounds that could add to it if you see any wavering with that roll away test.

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Old 01-07-2009, 06:19 PM   #3
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Acceptable Blower Vibration


Maybe this will help. With your power off try to grasp the drive wheel and wiggle the shaft front to back and side to side in its housing. Mine was noisey and the bushings badley worn a few years back. It would run and clunk , run and clunk and the belt slipped so I lost the smooth drive and velocity from the blower. I removed the shaft, gently washed out the fins with degreaser and a test tube brush and reinstalled with fresh bushings. If you have a bent or heavily clogged fin the cetrifugal force will make it shake a lot.
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Old 01-07-2009, 09:35 PM   #4
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Acceptable Blower Vibration


The squirrel cage is surprisingly clean - I guess the high efficiency filter is doing it's job. However, there is about 20 mils of wobble when I rotate the shaft. I think it was built this way as there's several balancing weights concentrated in one area (no evidence that any have fallen off). The motor bearings appear to be in good shape. There's a small amount of axial play but radially they're tight, and they feel smooth and quite when rotated by hand. Again, with everything all closed up there is very little noticeable vibration (you don't hear it, but you can feel it if you put you hand on the furnace). Would you expect a properly operating blower to have almost no noticeable shaking, or is a little expected? If it hadn't loosened up I would not be concerned with how it's operating.
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Old 01-07-2009, 10:13 PM   #5
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Acceptable Blower Vibration


Could be the drive pulley worked loose but the wobble doesn't go away, it's the sign of more things to come... and these things generally break down under load when you need them most.
I am not an HVAC guy but have rebuilt many motors with fans.The pull on one end of the shaft will eventually wear out the bushings once they start to wobble. Check your belt tension, etc. for slippage. Also check your pulley for alignment with the belt off. turn the pulley by hand and listen and look for signs of wear. If you rebuild check the shaft and both bushings.
If this is a traditional blower unit you can probably yank it out, replace the bushings and clean the fans within an hour on a moderate temp day. However never underestimate the value of a thourough internal furnace inspection by a trained tech.
My wife pointed out the lack of heat and air flow in ours just as I was preparing for an out of country business trip. I gambled on the blower rebuild and won. It's lasted another 7 years but now the furnace is due for replacement.
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Old 01-08-2009, 07:34 PM   #6
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Acceptable Blower Vibration


Thanks for the suggestions!
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Old 01-09-2009, 07:58 AM   #7
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Acceptable Blower Vibration


just a thought on that squirrel cage/motor assembly......how does it come out ....sliding out or drop down,and how does it secured going back in?might consider slipping a piece of wood on each side of the bottom of the squirrel cage housing round and to the base of the unit to see if you quiets up.
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Old 01-09-2009, 08:18 AM   #8
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Acceptable Blower Vibration


I have a heil high efficiency furnace that developed a bad vibration in the squirrel cage blower. I couldn't see any obvious reason for the vibration so I had it checked by a pro. They couldn't find anything either, but washed it off and wiped it down just in case there was enough light dust to cause it? Eventually, I ordered a new squirrel cage blower (not the motor, just the cage) and replaced it. In my case it took care of the vibration. I checked the old cage over and couldn't see any place where there were lost weights or damage. I have heard since that some spot welds can come loose which can change the balance points and cause vibration. I couldn't see any obvious splits, but, maybe that was the cause. In any case, replacing the cage solved my vibration issue.
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Old 01-09-2009, 09:47 AM   #9
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Acceptable Blower Vibration


Some installations I have worked on with other fan type motors come with rubber bushings or high density foam to absorb vibration and torque on start up.
While that will help dampen the vibration I would still be searching for the cause because these items eventually fail when you need them most. Any one fin with slight weight offset or bend could cause the vibration unless the fin directly opposite was equally out of balance....Given enough fins, in a pinch you could remove a damaged fin and its direct opposite to regain balance, but you would reduce your air flow.
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Old 01-10-2009, 10:44 AM   #10
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Biggles, it slides in to a couple of tracks along the top and is secured by 3 screws. This is a direct drive unit, with the motor itself supported by three legs that are anchored to the blower housing through rubber bushings. It's pretty quite now, probably thanks to the rubber mounting bushings, but it is vibrating. My concern is that imbalance puts extra load on the bearings, and may likely reduce their life.

iixeb, sound like your situation was exactly the same as mine. A new motor is about $210, while a new blower wheel is only about $85. If I knew that a new wheel would run much smoother I'd probably just buy a new one for piece of mind. Without any hands-on experience, I don't have a sense of what acceptable imbalance is. It's probably worth spending the money. I doubt it will be worse than it already is.
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Old 01-10-2009, 10:58 AM   #11
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Acceptable Blower Vibration


You will never get a perfectly balanced squirrel cage wheel. They all have a bit of side to side waver. I would not worry about it. They will eventually warp/get off balance if the previous owner never had it cleaned/got dust build up on the fins. The replacement wheel may be no better than the one you have now but you may want to replace it if it bothers you. I would do a temp rise check thru the furnace. Those tight filters have a BAD habit of overheating furnaces. Check the temp in the duct downstream from the bonnet 12" and subtract the return temp. Should have a allowable temp rise ie: 50-70 deg F on the model # sticker near the burners.
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Old 01-10-2009, 03:35 PM   #12
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Acceptable Blower Vibration


I believe I did pay about $85.00 for my new blower wheel. Mine mounts the same as yours, directly to the motor shaft, the motor supported in the blower cage housing with rubber bushings and the whole thing slides into the sheet metal tracks, which are a bit flimsy, the sheet metal is barely heavy enough to support the weight of the motor and blower. I had to drive about 27 miles each way to pick up the blower, it wasn't available locally. I did notice the inner rubber bushing holes were egg shaped, and I attempted to buy new. If I remember correctly, they weren't available locally either, so since I already had everything apart with the new cage in hand when I noticed the bad bushings, I rotated them 90 degrees and reinstalled them. So far, the new cage and the rubber motor mount bushings being rotated has worked.

Since I did both at the same time, I don't know which helped more? I had forgotten about the bushings until I read one of the other posts. I had tried putting blocks under the blower outer housing to lessen the vibration, but that only helped marginally. Having some experience in vibration damage from my work, I was concerned with the gas line cracking from the vibration I was experiencing with my unit. I think in my case, Heil under designed the 125,000 btu units, even out of balance, my unit vibrated excessively.

My furnace was installed by a professional installer, from a long established firm (that sadly has now gone out of business, naturally), and while it has lasted 18 years with minimal repairs, I think for the money, it should have been heavier built. IMHO
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Old 11-20-2010, 12:57 AM   #13
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Originally Posted by iixeb View Post
I believe I did pay about $85.00 for my new blower wheel. Mine mounts the same as yours, directly to the motor shaft, the motor supported in the blower cage housing with rubber bushings and the whole thing slides into the sheet metal tracks, which are a bit flimsy, the sheet metal is barely heavy enough to support the weight of the motor and blower. I had to drive about 27 miles each way to pick up the blower, it wasn't available locally. I did notice the inner rubber bushing holes were egg shaped, and I attempted to buy new. If I remember correctly, they weren't available locally either, so since I already had everything apart with the new cage in hand when I noticed the bad bushings, I rotated them 90 degrees and reinstalled them. So far, the new cage and the rubber motor mount bushings being rotated has worked.

Since I did both at the same time, I don't know which helped more? I had forgotten about the bushings until I read one of the other posts. I had tried putting blocks under the blower outer housing to lessen the vibration, but that only helped marginally. Having some experience in vibration damage from my work, I was concerned with the gas line cracking from the vibration I was experiencing with my unit. I think in my case, Heil under designed the 125,000 btu units, even out of balance, my unit vibrated excessively.

My furnace was installed by a professional installer, from a long established firm (that sadly has now gone out of business, naturally), and while it has lasted 18 years with minimal repairs, I think for the money, it should have been heavier built. IMHO
All,

I have this exact same problem. I replaced the motor and the blower wheel and I am still getting a lot of vibration. What can I adjust?
The cage isn't that well built. The Blower Wheel is pretty solid and it came balanced from the factory (I hope). The motor is brand new. The only things I fear are the flimsy cage, the flimsy motor bracket, and position where I attached the motor-bracket to the motor. I have the bracket more towards the Lead end of the motor, than the center of the motor.

Tomorrow, I am going to try re-adjusting that flimsy motor bracket

Has anyone else figured something else out? Any help appreciated!
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Old 11-20-2010, 08:36 AM   #14
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Acceptable Blower Vibration


A little bit of vibration is normal. If you put your hand on the side of the furnace where the blower is mounted you will feel some vibration on almost any furnace. I wouldn't worry about it if. I assume you got the squirrel cage locked onto the motor shaft at the its original position?
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Old 11-20-2010, 12:17 PM   #15
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A little bit of vibration is normal. If you put your hand on the side of the furnace where the blower is mounted you will feel some vibration on almost any furnace. I wouldn't worry about it if. I assume you got the squirrel cage locked onto the motor shaft at the its original position?

Thanks for your time.

The squirrel cage is secure.

I didn't put the motor in the same position since the old motor was OEM, and this new motor is after-market; the after market required an additional bracket (if I had known that, I would have just purchased the OEM motor).

I am going to go give it one last try and secure everything, put the motor like it was, etc.

Thanks!

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