Top 5 Best Bathroom Exhaust Fans With Humidity Sensors (2023 Review)

Imagine this: you walk into the bathroom, turn on the shower, and the bath fan automatically turns on when the humidity rises.

As a licensed inspector, I have seen numerous bathrooms with moisture and mold damage because the bathroom fan isn't used!

Well, humidity sensors will detect the moisture in the air and will turn on and off the exhaust fan without ever touching a wall switch.

Below is a quick list of all our top products. Keep scrolling to learn more about choosing and using the best bathroom fans with humidity sensors.

What Is A Bathroom Fan With A Humidity Sensor?

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.

How To Pick The Best Humidity Sensing Bathroom Fan?

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 Use A Bathroom Exhaust Fan With Humidity Sensor?

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.

Two Switches

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.

Motion Sensor

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.

How To Maintain The Bathroom Fan Humidistat?

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!

What Are The Benefits of Bathroom Fans With Humidity Sensors?

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