It's a paradox. Buy a bathroom exhaust fan powerful enough to vacate the room quickly of moisture and smells, and you run the risk of getting one so loud that no one wants to use it. Bring down the sound to quieter-than-Boeing-747 levels, and the fan may not be strong enough to do the job.
Quiet Bathroom Exhaust Fans
The perfect bathroom fan is both quiet and has sufficient room-clearing abilities.
Cost must be figured into the decision, as well, as it makes no sense to buy a quiet, efficient fan if it costs $800.
You'll find plenty of < 0.3 sones-rated bath fans out there. Unfortunately, you can't go on sones ratings only. First, let's define a few things:
Sones: Measuring Fans' Sound Levels
Sones, not decibels, are the units of measurement used when evaluating how loud a bathroom fan is. Sones are a subjective measurement, the psychological perception of a sound's intensity.
Single-speed bathroom fan sones range from 0.3 sones or less, for the very quietest models, to 4.0 sones or more for the loudest, so-called "economy" models.
CFM: How Fast Can It Move the Air?
CFM means "cubic feet per minute," referring to the volume of air that the fan will suck out of the bathroom within one minute. You can concentrate only on sones and get the quietest possible fan on Earth but the fan may not be sufficiently sized for your bathroom.
With all manufacturers, bathroom exhaust fans come in predictable CFM levels. For example, with a room that has 245 cubic feet, a 140 CFM-rated exhaust fan will clear the entire room in less than 2 minutes.
It's a Mixed Up World
This chart using sones and CFM data from a few popular brands shows how sones generally increase as CFMs increase.
Most of the < 0.3 sones fans move 80 CFM or less. Most of the 1.0 and greater sones fans move 140 CFM or more. But it's not quite that simple. As the chart shows, it's more of a zig-zag upward movement, with a few outliers moving more air with less noise:
|CFM||Sones||Single Sone Rating|
|140||1.0 - 1.5||140 - 94|
What Can 1 Sone Do?
It's helpful to standardize numbers by looking at Single Sone Rating (SSR), or the number of cubic feet per minute expelled per sone. Higher SSR numbers are better.
SSR is important because it standardizes sone-to-CFM "costs." It's best to have a fan that sucks out massive amounts of air at a lower noise cost, much like a car that goes farther on less fuel.
As an extreme example, look at the Broan Model 688, very much a bargain or economy fan that you might install in a cabin or rental property. At a noise level of a whopping 4.0 sones, it expels only 50 CFM. Its SSR is 12.5, lower than any other fan we surveyed.
Cost Matters, Too
One more dimension to consider is the Cost Adjustment Rating, which factors in the actual monetary cost of the bathroom fan (SSR/Cost) to help you see how much air movement coupled with low sones you are getting per dollar.
Higher Cost Adjustment Rating numbers are better.
For example, that earlier Broan 688 receives a miserably low Cost Adjustment of 0.9. Yet if you're looking for cheap, pure and simple, Broan 688 looks awfully good. It's a mere $14, more than 10x cheaper than the premium Panasonic FV-15VQ5 fan on our list below. To look at it another way, you could put fans in 5 to 10 residences for the price of one Panasonic.
3 Quietest Fans Rated (Adjusted)
1. Panasonic FV-15VQ5 WhisperCeiling
- CFM: 150
- Sones: 0.3
- Single Sone Rating (SSR): 500
- Cost: $152
- Cost Adjustment Rating: 3.28
- Comments: For shelling out big bucks for what is essentially a metal box, motor, and fan, you get a high CFM exhaust fan that's so quiet that homeowners report that they need to install timers because they forget that the fan is on.
2. Panasonic FV-11VQ5 WhisperCeiling
- CFM: 110
- Sones: 0.3
- Single Sone Rating (SSR): 367
- Cost: $120
- Cost Adjustment Rating: 3.06
- Comments: Panasonic's lower CFM offering puts out the same number of sones. But factoring in cost makes this one a great deal.
3. Broan Model # QTXE080 QTX Series Very Quiet
- CFM: 80
- Sones: 0.3
- Single Sone Rating (SSR): 267
- Cost: $100
- Cost Adjustment Rating: 2.67
- Comments: Broan is a familiar maker of fans, heaters, and range hoods, so they know this business. This QTX is lower in CFMs and even lower in price than both of the Panasonics. At $100, this one is a great deal from a solid manufacturer. Most small bathrooms will find 80 CFM more than adequate.
Other Sound Considerations
- Bathroom sizes matter. Larger bathrooms can absorb louder fan sounds better than small bathrooms.
- Duct size also determines fan noise. For example, fans with 6" ducts operating at 110 CFM with be quieter than fans with 4" ducts operating at the same CFM level.
From high school math, you may already know how to calculate the volume of a room (a box): Width x length x height = cubic feet. A room 7 feet long by 5 feet wide by 7 feet high has a volume of 245 cubic feet.