How To Stop Noise Coming From Bathroom Fan When Off (5-Step Guide)

Does anyone want weird noises from their bath fan when it's turned OFF?

In this guide, we'll cover...

  • How the backdraft damper causes noise
  • Why 'negative air pressure' can be make noises when fan is off
  • Tips to check the exterior cover for a loose flapper
  • And more...
noise coming from bathroom fan when off

Annoying sounds from a bath fan that is OFF can be a perplexing issue for many people.

Fortunately, there are typically just a few reasons why this happens and the solution can be relatively simple. The most common reason for weird sounds is that the backdraft damper is opening and closing rapidly.

This circular piece of plastic is meant to open when the fan is on to allow airflow, and to close off by gravity when the fan is off — there is one damper on the fan housing and one damper on the exterior cover.

Keep reading to learn the causes of this phenomenon and what to do about it!

What Causes Bath Fan Noise Even When Off?

There are typically just a few ways that an exhaust fan can make noise even if shutoff...

Noise #1: Wind

The backdraft damper or flapper on the bath fan housing (and exterior cover) is a circular piece of plastic that acts like a check valve that allows air to flow in only one direction towards the outside.

If the damper isn't closing all the way or if it's loose — the slightest bit of exterior wind or air pressure can rapidly pull the flap open and closed that makes a noise.

Noise #2: Resonance

Any other appliance in the attic or building (or even outside vehicles/trains) may be creating resonance or duct vibrations that leads to sounds even when your bath fan is off.

In a condo or apartment building, a neighbor's bathroom fan, dryer, or range hood may lead to sound being transferred to your bath fan duct.

Noise #3: Negative Air Pressure

If the bath fan duct incorrectly terminates in the attic or other unfinished space, then negative air pressure could be leading to sounds when the fan is off. Bath fan ducts should always go directly to the outside!

Any nearby appliances like attic fans can create suction when turned on which leads to the backdraft damper or flapper opening and closing — leading to annoying sounds.

Read Also >> How To Fix A Noisy Bath Fan?

Supplies And Tools Needed

  • 1/8" Thick Foam Weather Stripping
  • Balancing Wheel Weights
  • Screwdriver
  • Metal spring-loaded backdraft damper

5 Steps To Stop Noise Coming From Bathroom Fan When Off

Here are a couple ways that homeowners can fix a backdraft damper making a noise...

Step 1: Install Foam Padding On Exhaust Port Flapper

The exhaust port flapper is a circular piece of plastic that opens when the bath fan is turned on.

And when the fan turns off, this damper closes by gravity (or a small metal spring) in order to prevent air infiltration.

noise coming from bathroom fan when off

Bath fan backdraft damper in 'open' position

An easy fix is to install foam padding on the edge of the damper in order to reduce the noise.

To access this flapper, first remove the bathroom fan grille. Simply pull down on the grille cover until there is a 1-2 inch space. Homeowners will need to squeeze the metal clips in order to release the grille from the housing.

Depending on the style of bath fan, homeowners may need to remove the bath fan itself in order to access the damper.

Step 2: Install Weights 

Homeowners can attach a small weight to the flapper to give it more resistance to opening.

Wheel weights are a good option because they are small weights with an adhesive backing. The original purpose of these weights is to balance tires but they can be easily applied to a bath fan backdraft damper to reduce noise.

Read Also >> What Are Bathroom Fan Sone Ratings?

Step 3: Replace The Backdraft Damper

Just replacing the backdraft damper may fix the problem entirely.

Homeowners can install a 3rd party metal backdraft damper that includes a more robust spring-loaded flapper. The default flapper is typically plastic and quite flimsy.

A spring-loaded damper will have more resistance against air pressure or wind. If homeowners go this route, don't forget to remove the plastic flapper from the exhaust port.

Step 4: Install An Insulated Rigid Duct

If the bathroom fan is uninsulated and goes through an attic or other unconditioned space—it is more likely to make noise.

If the duct is the corrugated flexible type or if there are multiple bends, this may also increase noise. According to Energy.gov, gradual bends are always preferred over sharp duct turns.

noise coming from bathroom fan when off

The best duct is rigid metal and insulated that goes directly to the outside.

However, installing a new insulated flex duct is much easier than installing a new rigid duct — but doing either of these should help dampen the noises.

Of course, if it is a condo or apartment building, it may not be permissible to replace the duct and building maintenance should be consulted.

Step 5: Install Duct To Exterior Cover

If negative air pressure in the attic is leading to bath fan flapper noises, the easiest solution is to properly route the bath fan duct to the exterior.

Sometimes bath fan ducts are incorrectly laid LOOSELY over the attic floor or it's vented to the ridge without an exterior cover.

Read Also >> What Are The Best Quiet Bathroom Fans?

noise coming from bathroom fan when off (1)

Every time an attic fan, dehumidifier, or even air handler turns on in the attic, it can create a negative air pressure situation which affects the bath fan duct.

The bath fan duct should be installed to the exterior in order to avoid mold and moisture problems as well. The duct should be installed with an exterior cover that includes a backdraft damper.

And don't forget to seal all joints and connections of the bath fan duct.

RELATED: How Do Bathroom Exhaust Fans Work?

Final Thoughts

Bath fans making noise even when the fan is turned off can be a puzzling problem for many homeowners. There are typically just a few causes that can lead to noise when it's off like:

  1. Wind
  2. Resonance
  3. Negative Air Pressure

And the solutions include...

  • Installing the bath fan duct to the exterior with a proper cover
  • Insulating the bathroom fan duct
  • Adding foam padding or weights to the bath fan damper on the housing
  • Removing the plastic flapper and installing a metal spring-loaded backdraft damper

I hope you enjoyed this guide and let me know in the comments if you have any questions or want to share your experience!

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