What Are Bathroom Fan Sone Ratings? (2024 Guide On Loudness)

Do you want to know exactly what are bathroom fan sones?

Sones is a rating system for how loud things appear and they are used to rate bathroom exhaust fans.

In this guide, I will go over...

  • What exactly is the sone
  • At what sone level is quiet
  • How sones compare to CFM
  • The different levels of bathroom fan sones

Let's get started with this guide!

bathroom fan sones

What Are Bathroom Fan Sones?

Bathroom exhaust fan loudness is measured in sones. In fact, all home appliances such as the dishwasher, range hood, and washing machine --- their loudness is also measured using the sones rating system.

The basic thing to remember with the sones rating is that if you double the sones, the loudness is also doubled.

How Many Fan Sones is Quiet?

In my experience as a home inspector, if the bathroom exhaust fan sones is 1.0 or less --- that is considered a quiet (almost silent) ventilation exhaust fan.

These modern quiet bathroom exhaust fans are sometimes difficult to even know that they are on! I sometimes have to take a piece of toilet paper, and place it up on the bath fan grill. 

If the toilet paper sticks to the bath fan, then I know the vent fan is operating correctly.

If your bathroom exhaust fan is rated in the 2-3 sones range, I would say that is average to mediocre in terms of loudness. If the bathroom fan is 4 sones or more, then it is considered loud.

The most common "loud" bathroom exhaust fan in my area is the builder grade Broan 688 bathroom exhaust fan --- these fans have been installed for many years. These exhaust fans can literally be heard a room or two away even if the bathroom door is closed. They are rated at 4.0 sones.

By the way, if you have an older fan, and it is quiet, this may be a sign that it is broken or malfunctioning.

Read Also: The Best Quiet Bathroom Exhaust Fans (1.0 Sone Or Less)

What Actually Are Sones?

The sones rating is a way to measure perceived or estimated loudness.

Fan sones isn't actually a physical measurement like decibels. Sones is a rating system developed for how humans think how loud a sound feels.

The human test subjects who developed the sones rating were actually asked to give their opinion on how a loud a sound feels. This isn't a physical measurement, but it is a useful loudness rating scale.

If someone wants an actual physical measurement of sound level, the decibel is usually used. The decibel measures the physical sound pressure or level of a device.

Human Loudness Is Based On Frequency

Decibels aren't useful for humans because we can sense sound waves differently for higher and lower frequencies.

Humans can actually hear better when the frequency of the sound is higher. Take for example sound that is 20 decibels --- this is equivalent to whispering.

If this whispering sound is lowered to 100 hertz (unit of frequency) than humans cannot hear it. However, if you take the same 20 decibels, and increase the frequency to 500 hertz, then it becomes audible to humans.

This is why the sones rating was developed, because humans perceive loudness relative to the the frequency of the sound wave --- even if the sound level remains the same.

Read Also: Venting A Bathroom Fan Into An Attic (My Detailed Guide)

bathroom fan sones (1)

How Does Bathroom Fan Sones Compare To CFM?

Fan sones and CFM are probably the two biggest ratings for bathroom exhaust fans.

While the sone measures the loudness of the vent fan, CFM measures the fan speed or power.

CFM stands for cubic feet per minute which basically means how fast the bath fan exhausts or moves air. A 100 CFM rated fan means that it will exhaust 100 cubic feet of air per minute.

The lowest CFM fan you will find is likely 50 CFM which is suitable for small bathrooms.

75-100 CFM is rated for normal sized bathrooms.

Anything above 100-125 CFM is for larger sized bathrooms.

You want to get the right ventilation fan speed for your bathroom. If the CFM is too small, then it won't exhaust enough air (won't work well). If the CFM is too large, it will be louder than necessary, use more energy than necessary, and may even create negative pressure problems in the home.

Read Also: The Best Bathroom Exhaust Fans With Humidity Sensors (Automatically Turns On)

How Loud is 1 Sone?

One sone is equivalent to a very low hum.

When I do a home inspection, and the exhaust fan is rated at 1.0 sone or less, I will usually have to stop completely what I'm doing, and really focus on the sound --- it is almost inaudible.

If there are background noises, I will probably not be able to hear the bathroom fan at this sone level.

How Loud is 2 Sones?

At the 2 sones level, when you turn on the bathroom fan, you will clearly know that it's on. 

Even if there are background noises, there is no doubt about the fan being on. However, when you close the door, it is unlikely you will be able to hear the fan in adjoining rooms.

Read Also: How To Replace A Bathroom Exhaust Fan Without Attic Access

How Loud is 3 Sones?

A bathroom fan at the 3 sones level is on the level of background office noise.

You will be able to hear it in the hallway, but it is a bit more muted than the 4.0 sones level.

How Loud is 4 Sones?

When your bathroom fan reaches the 4 sones level or higher, it is equivalent to having a television on in a bedroom.

Even with the bathroom door closed, the vent fan will be able to be heard across the hallway or in an adjoining bedroom.

What's The Bottom Line On Bathroom Fan Sones?

The loudness of a bathroom exhaust fan is rated using a system called sones.

The sone isn't a physical measurement of sound, but rather how loud a sound "appears" to humans. Humans can hear some things at higher frequencies that we wouldn't be able to hear at lower frequencies --- even if the sound level or intensity is exactly the same.

Most exhaust fans that are 1.0 sone or less are considered quiet and may even be difficult to know that it's on.

Bathroom exhaust fans in the 2-3 sones range are considered average to mediocre on the sound loudness scale.

If your bathroom exhaust fan is 4.0 sones or higher, then it is a loud fan, and you will likely be able to hear it across the hallway even if the bathroom door is closed.

Read Also: The Best Bathroom Exhaust Fans With LED Lights (Extra Light Fixture)

Meet Your Home Inspector Secrets Author

4 thoughts on “What Are Bathroom Fan Sone Ratings? (2024 Guide On Loudness)”

  1. Hello, I need to replace my new exhaust that still has condensation around it after a hot shower. The rating is at 110CFM with .2 sone. I have a full bath that measures 5x7x9.

    • Hi Krishna… the 110-cfm should be satisfactory for that size of a bathroom. It may be related more to the duct that goes to the outside rather than the fan. Though the 110-cfm may not actually be reached if it is an old bath fan or off-brand. So you may just need to get a more powerful bath fan like 150-cfm or replace the vent duct. Flex ducts with ridges don’t vent as well as rigid metal ducting. There also may be a issue with the exterior cover obstructing airflow.


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