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Plumber installed a new Bradford White 75 gallon gas water heater with power vent. The first blower motor started a high-pitched whine/squeal (bad bearing?) approx 6 months after install. Motor was replaced, and it was fine for a month. New motor started loud HUMMING noise (not squealing, as before) a week later. Replaced that one, too. Third motor is now in place and also humming immediately after install.

I suspect the humming, which can be heard on the second floor, is similar to what a previous poster mentioned (harmonic resonance hum in PVC). The PVC vibrates, and I'm wondering if it is transferring this noise through the floor (which is our living room) joists. The plumber had also exchanged metal straps for plastic j-hooks because he thought that might help the vibration noise, but that made the humming worse. Any ideas on how to deal with this? It's not just an annoyance; you can feel the vibration through the living room floor.

Everything is within code in terms of distance and diameter of PVC venting. Plumber doesn't know what else to do....help!

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    If PVC is in harmonic resonance, you can move it out of resonance by changing its mass. Taping weights to it should do the job. If fan vibration is transferring physically to the PVC, then a foam/rubber coupling should lessen the transfer. Is the fan a bearing type, or a bushing type? The former, when well maintained, tend to vibrate less. – Wayfaring Stranger Jan 22 '15 at 22:46
  • Surely there is an appropriate sort of rubber or silicone coupling that can absorb the vibrations. – Aaron Brick May 19 '18 at 4:06
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If you think it is harmonic resonance, changing the length or diameter of the PVC pipe can help stop it. Refer to this prior question for more details: How do I prevent harmonic resonance hum in PVC vent of newly installed hot water heater?

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