Let's face the cold truth: not everyone uses bathroom fans when they should.
In an ideal world, people would turn on the bathroom fan when taking a shower or bath — and leave it on for 15-minutes afterwards.
The 'leaving it on after' part is important so the bath fan can properly remove all of the moisture which takes several minutes (depending on the fan). That's where humidity sensors come in.
A humidity sensing bathroom fan has a built-in sensor (humidistat) that responds to moisture in the air. Once the humidity reaches a particular level such as 55% relative humidity, it activates a switch to turn on the bathroom exhaust fan automatically.
Below is a quick list of my top products. Keep scrolling to learn more about important buying specs, choosing a wall switch, and my complete reviews of each exhaust fan.
1. Delta BreezSlim
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2. Panasonic WhisperSense
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3. Broan-NuTone Roomside
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4. Delta BreezSignature
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5. Broan-NuTone QTXE110S
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Our Overall #1 Rated Pick
Updated On October 15, 2021
We chose the BreezSlim by Delta because it includes a humidity sensor that will automatically turn the exhaust fan on and off. It was also designed for 'retrofit' installations and can use older 3-inch diameter ducts which makes it much easier to install. The LED indicator light is also bright enough to use as a night light.
Top 5 Best Humidity Sensing Bathroom Fans
In a hurry? Check out our top 5 bath fans with humidity sensors! Keep reading to discover more about our top picks.
6 Key Buying Considerations
There are a few things you should consider before buying a bathroom exhaust fan with a humidity sensor. Some of these things apply to all bathroom fans, but the first and second point only apply only to humidity sensing exhaust fans:
1. Humidity Sensor Adjustability
One of the most common complaint about humidity sensing bathroom fans is that the humidity sensor is too sensitive (or not sensitive enough).
The humidity setting is a knob or dial on the housing of the bathroom fan. You just need a flathead screwdriver to adjust the setting. In the picture above, the setting for this Delta humidity sensing fan can be changed from 50% to 80% relative humidity.
Sometimes the default setting of the humidity sensor is set too low, and if you live in a humid area of the country — it may keep your bathroom exhaust fan running 24/7. But if the humidity sensor is set too high, it may not turn on quickly enough when you need it to (or not turn on at all).
This doesn't mean that you shouldn't buy a bathroom fan that isn't adjustable, but it is something to keep in mind. Bathroom fans that have adjustable settings tend to be more expensive as well.
2. A New Wall Switch May Do The Job
Another thing to keep in mind is that you may not need to even replace the bathroom fan.
If you are perfectly happy with the performance of your bathroom fan, but you want the automatic control of moisture — then you may want to just install a new wall switch. There are custom wall switches that have humidity sensors built right into the switch itself. This means that you can replace the wall switch and not have to replace the entire bathroom fan assembly. You can see an article I wrote on the best wall switches for bathroom fans right here.
3. CFM or Fan Speed
As with all bathroom fans, you need to size it correctly for your bathroom. The strength of bathroom exhaust fans is measured in CFM, or Cubic Feet per Minute. This metric will basically tell you how much air the fan can remove within one minute. A general rule for sizing your fan is to measure the floor of your bathroom, and add 1 CFM per 1 square foot of floor space.
For example, if your bathroom floor measures as 80-sf, then you would want a bathroom fan with at least a 80-CFM rating. And for bathrooms larger than 100-sf, then you may want to start adding CFM’s based on how many fixtures you have in the bathroom. I wrote a detailed guide on choosing the CFM or fan speed for bath fans here.
4. Housing Size
The housing size is the metal box or frame of the exhaust fan, not to be confused with the removable cover or grill which is usually larger. The housing is the bulk of the fan that will actually be screwed to your ceiling joists (or fastened to a bracket).
It's a good idea to measure your existing housing size and ceiling joists before you make your purchase. You can always add wood blocking to the ceiling joists if the fan is too small but it requires more work.
Is the housing too tall for your ceiling cavity?
However, if the fan is too tall or thick, then you can run into problems. As an example, if you buy a bathroom fan that has a 8-inch thick (height) housing, and if you have an older home with 2" x 6" ceiling joists — it simply will not fit.
5. Noise Levels
The noise level of a ventilation fan is measured in sones which is a simple measurement of loudness. In general, a bathroom exhaust fan that is 1.5-sone or less is considered quiet, anything below 1-sone is extremely quiet. The basic idea is that if you double the sones, you double the noise level.
Some occupants may actually want a slightly louder fan because it is a type of “white noise” and gives some privacy when using the bathroom. Other homeowners may want a whisper quiet fan for a variety of reasons such as not waking up a child.
6. Duct Size
As with all bathroom fans, you should consider the duct size. Many new bathroom fans require a larger duct to the exterior such as 4-6 inches. Most older bathroom fans only use a 3-inch diameter duct. Of course, you can always buy a 3 to 4/6 inch duct adapter and still install the fan, but you won't get the stated performance out of the new fan. It may also be significantly louder than expected because of the small duct.
That is one reason that my top pick goes to the Delta BreezSlim because it is designed to use a 3-inch duct so you don't have to change it. And frankly, most old bathroom exhaust fans use a 3-inch duct. I invite you to also read my guide on the best ducts for bathroom fans right here.
How To Control It?
You really should decide on how you will control the bathroom exhaust fan before your purchase. What you decide depends on who will be using the bathroom such as if it is for yourself, guests, or children. Here are few options:
Single Wall Switch
Bathroom exhaust fans with humidity controlling sensors are usually controlled by a single wall switch. The common install is like this: you flip the wall switch once to turn on humidity sensing mode (auto) and toggle the switch twice to go into manual (high speed) mode. The 'toggling the wall switch twice' can be a problem for a guest bathroom since they probably have no idea about how to go into manual mode.
No Wall Switch
If the switch toggling may be an issue, you may want to wire the fan without a wall switch so that the humidity sensing mode is always on. Just to be clear, if you wire the fan without a wall switch, you can't turn it on manually to only remove smells.
This may be the best option for kids bathrooms or investment properties where you are concerned about bathroom damage due to the occupants not using the fan.
Another option is to have the bathroom fan wired to a separate switch if the fan also has a light or heat lamp. This way you can operate the exhaust fan and light separately. Remember, if you want to add an additional switch, you will have to add extra wiring.
In addition to humidistats, the bathroom fan may also have a motion sensor that works together with the humidity controlling sensor. So if someone just walks into the bathroom, the fan will turn on (usually at low speed). And then after a set period of time, like 10-minutes, the bathroom fan will turn off when it doesn't detect movement and the humidity has dropped below the target level.
Keep The Humidity Sensor Clean
There is one new maintenance requirement with humidity sensing bathroom fans: you need to periodically clean the humidity sensor.
If the humidity sensor gets dirty, then it simply won't work properly.
It may be turning on and off at weird times (or not turning on at all) just because it is dirty.
The easiest way to clean the humidistat is to use a brush attachment on a vacuum. First you should clean the grille with the brush attachment because a dirty grille can also affect the functioning of the humidity sensor. After cleaning the grille, remove the cover so that you have access to the humidity sensor — and then thoroughly clean it.
But don't use any harsh chemicals to clean the sensor!
These moisture sensing exhaust fans are perfect if you don’t want the hassle of remembering to turn it on, or if you have family members or tenants whom you think are not mindful of turning on the exhaust fan after showers.
Many people are unaware of how excess moisture can damage a bathroom and lead to poor air quality. During my home inspections, I can clearly see how mold on grout or caulking can leave a bad impressions with new buyers. When an occupant takes a shower but doesn't turn on the exhaust fan, the moisture will linger on the ceramic tiles much longer.
How many times do people accidentally leave the bathroom exhaust fan on the whole day?
This habit not only wastes electricity but it also pushes out conditioned (heated or cooled) air to the outside. It's equivalent to having an open window in the home all day long.
Also, using a fan with a humidistat switch can even help prevent a fire hazard. When occupants keep a bath fan running continuously for long periods, the fan becomes more susceptible to heat buildup (especially if the motor is dirty), and may one day catch on fire.
Protect Your Bathroom
The great advantage to having an automatic humidity sensing mode with a bathroom fan is that it will protect your bathroom from deterioration and mold.
Moisture is the number one enemy of bathrooms, it will literally rust the door and cabinet hardware and even any metal water lines. If there is one place you don't want rust, it is on the water supply lines to the vanity and toilet. If the water lines leak or burst, it can cause significant damage.
I remember I did a home inspection once where half of the ceiling was removed by the seller. I asked him what happened and he told me that one of the bathroom sinks was leaking on the second level, and they were away on vacation. The total damage probably exceeded $15,000.
Our Reviews of The Best Exhaust Fans With Humidity Sensors
The Delta BreezSlim (SLM70H) is my overall top pick for the best bathroom fan that can turn on/off based on humidity. This 70-cfm bathroom fan has an automatic humidity sensing mode as well as a manual mode. For the manual you mode, you will have to override the humidity sensor by toggling your wall switch twice.
The BreezSlim is also a pretty compact exhaust fan, so it is good for 'retrofit' installations where you are replacing an older bath fan. It is also designed to be used with 3-inch ducting which is usually what older bath fans use so you don't have to change the duct—saving a lot of work. In fact, since it is so much easier to install, that is why it is my top pick even though the humidity sensor isn't adjustable.
The BreezeSlim is also approved to be installed in the ceiling or the wall (vertical installation) and it is UL-approved to be installed above a shower or tub if connected to a GFCI circuit.
It has two LED light indicators on the fan grille which helps to show you which fan mode that it's in — and also whether the fan is on. When the BreezSlim first turns on with low speed, it can be very difficult to know it is activated without the indicator light. The blue LED indicator light is also powerful enough that you can use it as a night light.
How The Humidity Sensor Works For The BreezSlim?
The humidity sensor will automatically turn on the bathroom exhaust fan when it detects the humidity is past 60%, and then turn it off when it drops below 60%. There is always some wiggle room in the 60% level, so don't expect it to be exact. And if you have a house with high humidity, it may keep the bathroom fan on at low speed for long periods.
My second top pick goes to the WhisperSense by Panasonic (FV-0511VQC1). I'm sure you have heard of Panasonic which is a renowned global Japanese electronics company — and they make some of the best bathroom exhaust fans.
I think the most unique feature of the WhisperSense is that it has a switch on the fan housing that lets you choose between 50, 80, or 110-cfm fan speed. You can start out with a lower CFM, but if you aren't happy, you just remove the cover and flip the switch to a higher setting.
And the humidity sensor switch is also right next to the CFM selector on the housing. The cool thing about the moisture sensor with this Panasonic fan is that you can adjust the humidity level. One of the biggest complains of humidity sensing bathroom fans is that they can be too sensitive. Setting the humidity sensor to around 80% is recommended so it will only turn on when someone takes a shower.
On top of the humidity sensor, the WhisperSense also comes with a motion sensor. The motion sensor is another great way to control the bath fan (or forcing people to use it!). This feature is usually set to turn on when someone enters the bathroom, and then it turns off after they leave. I recommend setting it to run for 5-15 minutes after someone leaves the bathroom. The motion sensor is excellent for when someone goes #2 (the humidity controller is only for showers/bathing).
The biggest downside of the WhisperSense is an overly sensitive motion sensor. The motion sensor can be problematic and it may turn on just when you walk past the bathroom. You can overcome this problem by pointing the motion sensor away from the door (or putting tape on part of it). And the same issue applies for the humidity sensor, but since it is adjustable, you can always increase the humidity level that will turn on the vent fan — so it's less of an issue.
It is important to note that the WhisperSense is designed to be used with either 4-inch or 6-inch diameter ducts. So if you have an old bath fan that uses 3-inch ducting, you will need a duct adapter. Unfortunately, you won't get all of the performance out of the WhisperSense fan unless you upgrade to a 4 or 6-inch duct.
The installation bracket provided for the WhisperSense may be difficult or impossible to use with a bathroom fan replacement — it is designed for new construction. If you are replacing a fan, I would just install the fan housing directly to the joists using deck screws if you have trouble with the bracket.
If you are looking for a humidity sensing bathroom exhaust fan that also has a light — then the Broan-NuTone Roomside is a good bet. The Roomside is rated at 110-cfm and it comes with an integrated LED light and humidity sensor.
And like the Panasonic WhisperSense, the Roomside also has a switch on the housing that allows you to adjust the humidity sensitivity. By default it is 80% so if you don't think it is turning on when it should, you may need to adjust the humidity level lower.
You can wire the light to a separate switch from the fan or you can wire them both to the same switch. The LED color temperature is 3500-kelvin which does have a slight bluish tint. One downside with the light is that if you are unhappy with the color, you can't change the light for something else — since it is an integrated LED chip panel. You may want to install a dimmer switch since the full powered light may be too bright.
One cool feature of the Roomside is that it comes with a built-in timer that is adjusted on the housing. This allows you to cycle the fan (toggle the switch) and then it will automatically turn off the fan without having to install a wall countdown timer.
How To Install It?
The Broan-NuTone Roomside exhaust fan uses a 4-inch duct, so if you have an older 3-inch duct you will need to buy a separate 4-to-3 inch adapter. Just remember that if you don't upgrade to a 4-inch duct, then you won't get the full stated performance out of the fan.
Similar to the BreezSlim, the Roomside has a thin profile so it can fit in 2x6-inch joists — it has a housing depth of 5.75-inches. It also has a large round 'adapter plate' that goes over the housing and attaches to the grille. Since this plate is so large, it will easily cover any drywall cuts. Broan-NuTone designed the BreezSlim to install easily in old construction.
The BreezSignature is another great choice by Delta for a bathroom fan that includes a moisture sensor. This fan is a bit more powerful than my other picks and it tops out at 130-cfm on high speed.
Variable Speed Motor
On lower speeds it will run at lower CFMs and the fan speed changes because it is a variable speed motor. The nice thing about variable speed motors is that they are more efficient and the speed can adjust to get the desired performance. There is a so-called soft start when the bathroom exhaust fan turns on (a low CFM) and then it will eventually speed up.
A common issue with the old version of the BreezSignature is that the bathroom fan would be running constantly because of an overly sensitive humidity sensor. But the new version as of April 2021 includes an adjustable humidity sensor — change it from 50% to 80%.
This humidity sensing bathroom fan by Delta is also ultra quiet when on low speed. For low speeds, the sone level is less than 0.3, and on high speed it is around 2 sones. This fan also has a blue and amber indicator light so you can know that the fan is on and which mode it is using (humidity or manual). The blue LED light is also bright enough so you can use it as a night light.
Like pretty much all bathroom fans with humidity sensors, this BreezSignature can have the humidity mode overridden by simply toggling the wall switch off and on.
The QTXE110S is another Broan-NuTone bathroom exhaust fan that will automatically dehumidify your bathroom.
One cool thing about the QTXE Series fan is that it has a humidity sensor and a timer (similar to the Roomside fan). The factory default setting is a 20-minutes delay, so it will turn off the fan once it drops below the humidity level (and 20-minutes elapses). Both the humidity sensor and the timer is adjustable on the housing — you just need a screwdriver. The humidity sensor can be adjusted between 50%-70% and the timer can be set to 5-60 minutes.
The biggest differences between the Broan-Nutone Roomside and the QTXE110S is that the Roomside has a light and it is a bit louder. The QXTE Series fan is extremely quiet and it comes in at only 0.7-sones on high (Roomside is 2 sones). The Roomside also has has a circular shaped cover while the QTXE cover is square.
The QTXE110S also has a variable speed DC motor so the fan will speed up or slow down to improve performance. Since it is variable speed, it should still reach most of the stated CFM even if you have a poor duct installation.
This fan is designed to be used with a 6-inch duct, so you definitely won't get all of the performance out of this fan if you don't upgrade your duct. The QTXE is meant to be installed in new construction as well (it won't fit 2x6 joists) so you may have to open up the ceiling a bit to get it to fit. Only one side of the housing can be attached to the joist, but it comes with adjustable hanger bars which can help.