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How can I reduce noise and vibration that's transmitted from an an attic gable fan to the rest of the house? Currently, the fan is mounted via screws to studs on the gable. Even when the fan is running at its lowest speed, when the house is quiet I hear a low-pitched hum, even when I'm two floors below the attic.

A few related questions:

  • I'm preparing to change (based on this answer) from directly mounting the fan to studs. Instead, I'll be mounting the fan to a plywood sheet with a fan-sized hole cut in the middle, and mounting that plywood sheet to the studs. Is mounting to plywood likely to change the vibration characteristics of the fan?
  • Is there a particular way I should mount the fan to the plywood to reduce vibration? The fan has two pairs of mounting brackets that are asymmetrical: there's a pair of brackets on each side of the fan (each about 3 degrees from each other), not 4 brackets spaced 90 degrees apart. Should I put the mounts on top & bottom or left & right? Or does it not matter?
  • Is there any particular way I should mount the plywood to the studs that may dampen vibration?
  • Are there vibration-dampening screws or mounts that are strong enough to hold up a 25 pound fan? And if so, should I use them between fan and plywood, or between plywood and studs? (Note that I'll still need to have an air-tight seal between the fan and plywood, and plywood and studs, to prevent backdrafts.)
  • Should I put a layer of foam, neoprene, or some other material between plywood and studs, or fan and plywood, that may dampen vibrations? If yes, what's a good material to use? Or is this a waste of time because vibration is mainly transmitted through the screws and unless I replace screws with different mounting hardware then it won't solve the problem?
  • Should I wrap the outside of the fan's cylindrical housing with a vibration-dampening material, and if so what is a good material to use?

BTW, this is a follow-up to Sealing air gaps around edges of attic gable fan.

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  • i would put a few rubber washers between metal washers around the screws to absorb vibration w/o a loss of strength. You might also be able to better balance the fan blades by grinding notches out of the heaviest blades.
    – dandavis
    Apr 11 at 3:17
  • Do a static balance.
    – Solar Mike
    Apr 11 at 3:57
  • They make devices called vibrato dampers, try a few of them.
    – Gil
    Apr 11 at 5:18
  • @dandavis grinding down the fan blades sounds like a recipe for ending up with no blades... Blade 1 is too heavy grinds. Dang! now Blade 2 is the heaviest grinds. Ooops, now Blade 3 is the heaviest grinds. Hmmm... Blade 1 is heaviest again grinds Lather. Rinse. Repeat. Well, I don't have any blades left - they're all just nubs. Maybe a file, not a grinder...
    – FreeMan
    Apr 11 at 12:03
  • They do make balancing kits small stick on pads of lead I don’t care for them, many times a bent blade can be the problem rubber pads help but stud mounts where only rubber between the 2 steel plates or studs are the best.
    – Ed Beal
    Apr 11 at 16:54

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