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Old 10-15-2012, 01:30 PM   #1
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Furnace Blower Wheel diameter question


I am replacing the blower motor and wheel on my furnace. The problem I am having is I cannot find the diameter blower wheel that I need. I've visited 4 HVAC stores with the wheel in hand and none of them have a match. Searching online yields nothing either. I can find one that matches up every size and spec except I have to make a choice between going slightly larger or slightly smaller on diamater.

The current wheel is roughly 11-7/8". I can either go down to an 11" diameter or up to a 12-3/16". Assuming there is room in the blower enclosure, my thought was to go up to the slightly larger wheel. Is there anything I am overlooking with that decision?

Thanks in advance!

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Old 10-15-2012, 04:33 PM   #2
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Furnace Blower Wheel diameter question


"The issue is clearance, Clarence." The larger diameter wheel must still be installed so the blower wheel fits rather snugly into the housing yet not rubbing.

I had the same problem with my external exhaust vent for my kitchen. The clearances were too tight to go larger, so I went smaller and fabricated a plastic ring out of an old frisbee to fill the gap and provide proper tolerances for good air flow.

Here's a typical installation - note the tight clearance at the round ends of the fan cage.... this is what creates the pressure differential when the fan spins. It is only because HVAC is low pressure air that you can get away with any clearance at all.



Generally smaller is the only direction you can go in due to these tight clearances - the critical match is right where the ends of the squirrel cage interact with the housing. Even a small change in this clearance (for example, with a smaller squirrel cage) will require the fabrication of some kind of rigid gasket to make the gap correct.

May I ask what is wrong with your old one fan wheel? It might be best to have it straightened or repaired if necessary vs replacing with the wrong size. They last pretty much forever unless someone has destroyed it trying to pull it from the motor.


Last edited by imautoparts; 10-15-2012 at 04:36 PM.
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Old 10-16-2012, 03:26 PM   #3
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Furnace Blower Wheel diameter question


Thanks for the detailed reply, imautoparts. The reason I was looking to replace it is because for some reason the blades were incredible rusted to the point where they where corroding away in places. We've only owned the home for 5 months, so I'm not sure what went on before. I assume they must have had some pretty bad leaking to get that much water in there. Anyway, that was the primary reason I was looking to replace it.

After reading your post I called our local Bryant shop and pressed them to track one down. Given the furnace model number the guy was able to find the exact one I needed. Now I've gotta wait for it to come in and then take my time installing the new motor and wheel.

Thanks for your help!
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Old 10-16-2012, 05:04 PM   #4
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Furnace Blower Wheel diameter question


get the one as close to yours ....don't overthink it...it will work...ben sr
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Old 12-13-2012, 11:28 AM   #5
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Furnace Blower Wheel diameter question


Thanks for the help, guys. I forgot to follow-up until now. I ended up finding a new blower wheel that matched the exact size through the local Bryant repair shop. Replaced the motor as well and she's working great.
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