Choosing a bathroom exhaust fan often presents a paradox. If you buy a fan that's powerful enough to quickly clear the room of moisture and odors, you run the risk of getting one so loud that nobody wants to use it. On the other hand, if you bring down the sound to quieter-than-Boeing-747 levels, the fan may not be strong enough to do the job.
Of course, the perfect bathroom fan is both quiet and has sufficient room-clearing capability. Cost also must be figured into the decision, as it makes no sense to buy a quiet, efficient fan if it costs $800. You'll find plenty of fans with a low sone rating, the standard measure used for fan noise, but you can't go on a simple sones ratings alone. Consider a few more factors to make a more informed decision.
Measuring Fan Sound Levels
Sones, not decibels, are the units of measurement used when evaluating how loud a bathroom fan is. Sones are a subjective measurement, based on the psychological perception of a sound's intensity. Single-speed bathroom fans 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.
Measuring Air Movement
The effective power of a bathroom exhaust fan is measured in cfm, or cubic feet per minute. This is 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 fan possible but that won't ensure that the fan is sufficiently sized for your bathroom. The latter is where the cfm rating comes in. As a very general rule, the minimum cfm for any bathroom is 50. After that, you should have about 1 cfm per square foot of room area. For example, a 10 x 10-foot bathroom needs a fan rated for at least 100 cfm.
Tip: To take full advantage of your fan's cfm capability, you need to supply enough intake, or "makeup," air by leaving the bathroom door sufficiently open while the fan is running. Fans don't just suck out bad air; they create air exchange by pulling in fresh air at the same time. If you starve the fan of makeup air, it won't do its job very well.
It's a Mixed Up World
The following chart using sones and cfm data from a few popular brands shows how sones generally increase as cfm increase. Most of the < 0.3-sone fans move 80 cfm or less, while most of the 1.0-sone and louder 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.
Enter the Single Sone Rating (SSR), the number of cubic feet per minute expelled per sone (sones/cfm). 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, consider 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.
|CFM||Sones||Single Sone Rating|
|140||1.0 - 1.5||140 - 94|
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, the previously mentioned Broan 688 receives a miserably low Cost Adjustment of 0.9. Yet if you're looking for cheap, pure and simple, the Broan 688 might look awfully good. At a mere $14, it's many times cheaper than the premium fans in our list below. To look at it another way, you could put fans in 5 to 10 residences for the price of one high-quality unit (not counting installation cost, of course).
Quietest Bathroom Exhaust Fans Rated
Here are three of the better fans on the market. There are certainly more fans with similar performance and sone ratings, but looking closely at a few helps you understand how to choose a quiet bathroom fan that meets your airflow needs as well as your budget.
1. Panasonic FV-15VQ5 WhisperCeiling
- CFM: 150
- Sones: 0.3
- Single Sone Rating (SSR): 500
- Cost: $134
- Cost Adjustment Rating: 3.73
- 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: $103
- Cost Adjustment Rating: 3.56
- Comments: Panasonic's lower-cfm offering has the sone rating as their FV-15VQ5 unit, but factoring in cost makes this one a great deal.
3. Broan QTXE080 QTX Series Very Quiet
- CFM: 80
- Sones: 0.3
- Single Sone Rating (SSR): 267
- Cost: $110
- Cost Adjustment Rating: 2.43
- Comments: Broan is a familiar maker of fans, heaters, and range hoods, so they know this business. This QTX is lowest in cfm without offering the lowest price. Still a good fan for money and perhaps the best choice for small bathrooms that don't need more than 80 cfm.