For decades, people have been talking about the “bones” of a house, but nobody ever talks about the organs of a house. No, I don’t mean the piano that your grandma played at church. I mean the parts of a house that help it function properly. The components that run without us having to think about them. As humans, we rarely stop and think about how our organs are working. The same concept applies to a house. We don’t think about our toilets flushing, or our water heater running; we just expect them to work when we go to use them. What about the things like your bathroom exhaust fans?

Bathroom exhaust fans are often an afterthought to homeowners. If it sounds like it’s working, it must be working, right? That tiny fan that runs while you shower does a lot more for your home than you think.

Benefits of Bathroom Exhaust Fans

wet dog in a bathtub

The bathroom is a hotbed for some of our worst enemies. Bacteria, odors, and moisture can all reside in your bathroom and spread to the rest of your home if you’re not careful. A functioning exhaust fan protects your home by sucking some of those nuisances outside. Here is a quick list of the benefits of exhaust fans:

  1. They get rid of some of that airborne bacteria that like to float around your living space.
  2. They can eliminate those awful smells that want to linger around the bathroom. Causing more grief than most people would wish to admit.
  3. This one is perhaps the most important. Bathroom exhaust fans help cut down the humidity of the air. When a person showers or takes a bath, there is the issue of moisture. Too much moisture without ventilation can result in mold and mildew. That doesn’t just apply to the bathroom, either. Mold can grow in any part of the house if there is too much moisture. This excess can result in a toxic environment for anyone who lives in the house.
  4. I am piggybacking off of the last one here, but the exhaust fan can also help fight back against the foggy mirror problem. Everyone hates a foggy mirror.
  5. The bathroom isn’t the only beneficiary of an exhaust fan. On top of mold spores, it can reduce the levels of dust and other allergens, improving the overall quality of your home’s air.

Bonus** If you’re like me, you have probably used the bathroom fan as soundproofing while you were visiting someone else’s house. Don’t lie.

Walk Me Through the Numbers

When buying a home, it’s likely that the bathrooms already have bathroom exhaust fans installed. If a bathroom does not have any windows (or at least an openable one), then it needs to have a ventilation fan. If you are doing some remodeling, or just want to upgrade, there are a few things you will need to know.

clean bathroom with white towels

When it comes to ventilation power, fans are rated with a simple metric. This measurement is known as cubic feet per minute (or CFM). This number shows how quickly the fan sucks the air out of the bathroom. To accurately determine the necessary CFM, Home Depot outlines a simple formula. You want to find the total amount of cubic feet and multiply that number by .13, or length x width x height x .13. This method will present you with a rating that you should aim for while installing the fan. A bathroom should never have a fan that is under 50 CFM, but there is usually no need for a fan over 100 CFM.

Another rating you may want to take into consideration is the sones, which is responsible for determining how quietly a fan runs. The lower the sone rating is, the softer the fan will operate. Most people consider over 4 to be too loud, but if you recall, louder fans serve a purpose also (see bonus above).

Different Types of Bathroom Exhaust Fans

Now that you know what the relevant numbers mean, you can select which type of fan you want to install.

  • The most common type of exhaust fan is the ceiling fan. This simple setup reigns supreme in the ventilation world. The ceiling exhaust fan is low-profile and easy to install. A person could also choose to do an in-line exhaust fan. These are typically smaller and placed in less obvious places. In my opinion, the closer the fan is to the source of moisture, the better.
  • After you have chosen the type of fan for your desired placement, you get to decide whether or not you want a timed fan. A bathroom fan timer may cost a little more but is extremely practical. I know I have left the upstairs bathroom fan on countless times; a problem that would have been solved by a timer switch. It is usually a small dial on the wall that lets you choose how long you want the fan to run. After the timer is up, the fan shuts off.
  • Some exhaust fans have light fixtures built-in, so they act as one unit. They operate as part of the same assembly and are connected to one switch. You will typically see them in bathrooms where the vanity and mirror are separate from the toilet and shower.
  • I spoke with Chip Gabbert, the owner of MVP Electric, Heating & Cooling in Lenexa, Kansas. He said there are also some luxurious fans. There are now moisture sensing switches that turn the fan on and off based on the humidity levels in the room. These fans tend to be more expensive, but they are also highly efficient. Chip also told me that some fans include Bluetooth speakers.
  • This option is meant more for homeowners in colder climates, but some exhaust fans are capable of incorporating heat lamps. Heat lamps are just an extra source of heat that can run in your bathroom. Beware! These little bulbs could be a pocket drainer if left turned on.

Costs of Running the Fan

I had the opportunity to speak with Wes Davis, the Vice President of Quality Assured Programs for the Air Conditioning Contractors of America (ACCA). He said that when it comes to cost and efficiency, bathroom exhaust fans will not usually be the culprit of high energy bills. Since it is a small fan, it is not using a great deal of energy. More often than not, it will be the light bulb attached to the fan that will cost more to use.

Energy Star tests and rates fans based on rules set forth by the US Environmental Protection Agency. A product that is Energy Star certified will operate more efficiently and save the homeowner money. I reached out to Energy Star to find out the monthly costs of running a bathroom exhaust fan. They recommended that the calculation of power consumption should be done using the following formula:

Power(W) = Airflow(CFM) / Efficacy (CFM/W)

You can find the values for airflow and efficacy here

Once you have the number for power consumption, you calculate the cost using the following formulas:

E(kWh/day) = P(W) x t(hr/day) / 1000 (W/kW)


Cost($/day) = E(kWh/day) x Cost(cent/kWh) / 100(cent/$)

The efficacy of a fan represents the overall efficiency of the fan. The higher the efficacy, the more efficient the fan is. From an efficiency and cost standpoint, we recommend an exhaust fan that is Energy Star approved.

Installation Basics

steam rising from a bath

After you have chosen which bathroom exhaust fan you are going to install, it is time to get to work. The amateur handyman can tackle this type of job in a day. A professional can probably knock out this task in about four hours. I never want to discourage a DIYer from DIYing, but if it deals with any electrical work, I recommend an expert. You can do all of the heavy lifting and then hire the electrician to come and wire it up. I spoke with Jeff Patterson, the owner of Home Repair Tutor. He teaches step-by-step courses on how to remodel a bathroom. He mentioned that if you are attempting to do the electrical work yourself, contact the fan manufacturer and they can help you with the electrical.

According to Chip Gabbert, if a homeowner has a correctly installed fan, they can get a new one placed for as little as $250. If a person requires new ductwork, the work for that can add around $300. The ending price will depend on the fan that the homeowner chooses. The lower end is that $250 I mentioned, with the higher end being as much as $2000. The more expensive jobs will include moisture sensing switches, ductwork, and more.

The most important part of installing an exhaust fan is figuring out how to fit the ductwork for the system. Wes, Jeff, and Chip all said that the key to ventilation is to make sure that the air gets terminated outside. Some older homes have the ventilation going up into the attic, where it can cause excessive mold and mildew. Damp, dark spaces are where mold thrives.

Deciding where to place your vent can be tricky. There are three different places that a vent can be positioned: the side wall, the roof, and the soffit. Wes mentioned that you should be strategic about where you place the vent. You don’t want to stick it in a spot where people are going to be spending time. The vent should never be put above a bedroom window, deck, or patio. Be sure to include a bug screen on that vent as well, preventing unwanted pests from entering your home.

Taking Care of Your Fan

cleaning a dirty bathroom exhaust fan

Once you have an exhaust fan installed (or already had one installed), there are some steps a homeowner can take to be sure that their air exhaust fans are working correctly. Usually, the first sign of a problem is an abundance of steam on the mirror. If you are noticing excess steam, it might be time to consider testing your fan. I asked an industry expert about ventilation testing. He told me that you could take a thin piece of toilet paper and hold it up near the fan. If the toilet paper is sucked upward by the fan, then it is functioning correctly. He asked me not to reveal his name because it’s not a recommended method. Nonetheless, it can produce decent results.

A common question about bath fans is, “how long do I need to keep it running after I shower?” Well, you can talk to ten different people and get nine different answers. We recommend letting your fan run with the door open for fifteen minutes after you shower. If your fan is doing its job, then the air should be clear after that amount of time. If you don’t have fifteen minutes, at least let it run until the steam on the mirror clears up.

Not many people think of this, but it is a good rule of thumb to clean your fan at least once a year. They can build up lint and dust, resulting in reduced airflow. I have read about stories of excessive lint on an exhaust fan leading to fires. Cleaning it is a simple task that shouldn’t take long. It is better to clean your fan and keep your air circulating, rather than putting it off and risking mold growth.

I hope that this has outlined the importance of your bathroom’s exhaust fan. Despite all of the technical aspects, they are a simple way to help take care of your home. Though it can be expensive, there are cheap options as well. If you take care of your fan, it will take care of your bathroom’s air. If you need a bathroom exhaust fan installed, one of our handymen would be happy to help you.