Thread: Attic Fan Vibration

While avoiding the debate over the risk/benefit/why-install-these-things-at-all...

A newly installed attic fan vibrates. The lateral deflection is minimal - think back massager, not a ceiling fan with one blade.

Short story: crappy fan or improper mounting?

Long story setup: 1,5500cfm attic fan with thermostat and humidistat. Manufacturer (AirVent, Inc model 53850) suggested use up to 2100sqft. (Attic is 1,500 sqft.). Stick framed roof with 1/2 in. OSB sheathing. Fan is installed about 2/3 of the way up a 28ft rafter. It's immediately alongside the rafter, also where a horizontal collar tie and a diagonal strut are nailed to the rafter.

Upside: lots of support
Downside: vibration radiates in all directions

The fan appears properly mounted from the outside and inside view. It was slid under the upper row of shingles and nailed into place. There is some deflection if I push on the fixture outward (from the inside), from what feels like flex in the metal flange. Viewed from the inside, the flex is about 1/4 inch gap between fan and shingles.

Are there tricks to better mounting, isolating the vibration, or simply R/R the unit? (yeah yeah, maybe just "R" and no "R/R")

Originally Posted by David Cloutier

Are there tricks to better mounting, isolating the vibration, or simply R/R the unit? (yeah yeah, maybe just "R" and no "R/R")

You got it ... just "R" and no "R/R"

My guess would be a bent/twisted fan blade. Some come with weighted clips on one blade to balance the fan and the weighted clip may have come off the blade, leaving the fan unbalanced.

You can "R" the fan, check the blades for alignment (ends all the same distance from a given point or surface) and same degree of angle of attack to the air (same twist), and make sure they all look to have the same 'bend' if they have a bend (some are straight but twisted, some have cupped up ends along with the twist). If the blades are all in alignment, then check balance by taping a small washer to one blade and moving it around (this is trial and error ... mostly error ).

Then, if you must, you can do the "/R" part.

If it is a brand new unit, replace it. It sounds (no pun intended) defective. These things are made to be mounted in the fashion you describe and should not have excessive vibration or noise.

Originally Posted by David Cloutier

While avoiding the debate over the risk/benefit/why-install-these-things-at-all...

A newly installed attic fan vibrates. The lateral deflection is minimal - think back massager, not a ceiling fan with one blade.

Short story: crappy fan or improper mounting?

Long story setup: 1,5500cfm attic fan with thermostat and humidistat. Manufacturer (AirVent, Inc model 53850) suggested use up to 2100sqft. (Attic is 1,500 sqft.). Stick framed roof with 1/2 in. OSB sheathing. Fan is installed about 2/3 of the way up a 28ft rafter. It's immediately alongside the rafter, also where a horizontal collar tie and a diagonal strut are nailed to the rafter.

Upside: lots of support
Downside: vibration radiates in all directions

The fan appears properly mounted from the outside and inside view. It was slid under the upper row of shingles and nailed into place. There is some deflection if I push on the fixture outward (from the inside), from what feels like flex in the metal flange. Viewed from the inside, the flex is about 1/4 inch gap between fan and shingles.

Are there tricks to better mounting, isolating the vibration, or simply R/R the unit? (yeah yeah, maybe just "R" and no "R/R")

Fan is unbalanced. The factory is supposed to balance, so R&R.

Thank for the evaluations. Update : new fan blade unit is on the way.

Of note, manufacturer recommends 5 square feet of air intake to the attic, and states that fan should have been placed within two (2) feet of the roof line.