Q&A / 

Bathroom Exhaust Fans

DEAR TIM: I have several inexpensive builder-grade exhaust fans in my home. They are noisy, and I don't feel they do a good job of getting rid of the moist air produced while showering. Is it possible to get high-performance ventilation with little or no noise? I would like a bathroom exhaust fan with a light. Can you tell me how to install a bathroom fan so I do not cause any damage to my home? Faith F., Mt. Crawford, VA

DEAR FAITH: Bathroom fans are a critical part of a home-ventilation system. A bathroom exhaust fan, improperly installed, can create all sorts of hidden damage to a home. All too often, installers just let the moist air escape into an attic space. This moist air can condense on the cooler surfaces in the attic. This liquid water on the wood surfaces creates mold and can lead to serious wood rot.

The good news for you is that the exact fan you are looking for is available. It has been around for years, but many builders choose to install cheaper fans to try to make their houses more affordable. The trouble is, I have discovered many consumers would gladly pay a slight upcharge if they were given the option of having great ventilation and less noise while in the bathroom. It is my hope that builders start to learn to offer home buyers more choices. But I feel that day may never come, as builders will argue that more choices equate to more problems.

This fan may look like an overweight flying saucer, but rest assured it does a fantastic job of vacuuming moist air from bathrooms. PHOTO CREDIT: Tim Carter

This fan may look like an overweight flying saucer, but rest assured it does a fantastic job of vacuuming moist air from bathrooms. PHOTO CREDIT: Tim Carter

I have had fantastic luck installing bathroom exhaust fans that are actually located in the attic space. They resemble central vacuum systems inasmuch as the fan motor is located perhaps 8 or 10 feet away from the bathroom. Most builder-grade fan motors are just inches away from the bathroom ceiling. This is one reason why they are so noisy.

These remote bathroom exhaust fans have insulated flexible duct pipe that extends from the fan motor to small exhaust inlet boxes that are attached to the framing members in your bathroom ceiling. The box extends up into your attic, and all you see on the bathroom ceiling is a sleek round inlet cover. The powerful fans can slurp up massive amounts of moist humid air that rises to the ceilings as you shower. This air is ducted through the roof of your home in a special roof vent cap that is easy to install.

I have found that it is often best to vent fans and dryers through the roof. I urge you to watch this video of mine to see how easy it is to install the correct vent-cap flashing on a roof. Have no fear - if done right you will have no leaks.

The flexible insulated ducting that extends from the roof to the fan, and then to your bathroom ceiling, does two important job: It helps to suppress noise from the fan, and the insulation prevents condensation from forming inside the flexible piping. Many people complain about a leaking bathroom fan, when in fact the water is not a roof leak but condensate water that forms inside of uninsulated exhaust piping and flows down the piping into the bathroom.

The bathroom exhaust fans I use come with or without lights. The ones with lights use brilliant compact halogen bulbs that fit into the center of the small circular vent covers. I always place two of these inlets with lights in each bathroom, one immediately adjacent to the shower area and the other toward the center of the bathroom. These lights produce good overall lighting for the average bathroom. You will need additional lighting above any mirror.

To avoid damage to your home while installing a bathroom fan, always follow the written instructions that come with the fan. If you are not comfortable working with high-voltage electric wire so it will pass inspection, then hire a competent electrician to connect the fan. The most important aspect is to duct the air from the bathroom to the exterior of the house. You should do this through the roof.

Avoid the temptation of venting your fan through the horizontal soffit that can be found in many roof overhangs. All too often the moist air billows up under the soffit and is sucked into the attic. If this happens, mildew and wood rot is a certainty.

Problems with bathroom exhaust fans can happen years later. The connections between the flexible duct pipe, the fan, inlet boxes and the roof vent cap must be permanent. Never rely on duct tape to secure these connections. The high heat and humidity in attics can cause duct tape to fail. It is better to use metal band clamps that are nearly identical to traditional automotive radiator hose clamps. These inexpensive clamps can be found at hardware stores, ductwork shops and some home centers. Once the band clamp is connected, then use tape as directed by the fan manufacturer.

Be sure there are no kinks in the flexible duct pipe. Also be sure to install a makeup air duct in your home that allows an equal amount of fresh air to enter your home for every bit of air the exhaust fan is expelling. If you do not have this critical makeup air, you could cause "backdrafting" to occur. This means poisonous gases are drawn into your home through furnace or water heater exhaust pipes.

Column 665


37 Responses to Bathroom Exhaust Fans

  1. Both my bathroom exhaust fans leak water and ruin the ceiling. They are each vented separately and appear to be adequately insulated. It only leaks during the cold winter months so it is condensation that is causing but how can it be stopped?

  2. I have had the best luck with a switch i bought that monitors the moisture/ condensation in the bathroom and automatically turns on my exhaust fan. The switch is called DewStop, I like it because nobody has to turn it on or off. My kids didnt remember to turn on the timer switch, with this I dont have to worry. It can be operated manually also. My fan wasn't the problem... it was getting it turned on that was the problem. Problem solved!

  3. Tim -- I like the remote fan options. I would like it to serve up to 3 bathrooms -- 2 of which have a shower. What is the most effective way to switch/operate the fan? Is it simply a 3-way switch? Or is there a standard way to allow any of the 3 locations to turn the fan on and keep it on for a long enough time?



  4. I was wondering, can I use 3 inch black ABS pipe to vent fan outside instead of the plastic type flex tubing?

  5. I have 2 bathroom fans that I need to vent into one vent cap. I have the ducts and a wye connection. Do I need some sort of baffle system to maintain proper pressure so I dont simply push the air from one bathroom to the other? The local big boxes dont seem to carry anythng like that. Any thoughts?

  6. Do you have a preference on roof vent caps? I am looking for one with screen to keep out birds, backdraft damper that will not clank open and shut on windy days.

  7. Looks like there are bits of shredded, brown leaves hanging down from our bathroom exhaust fan. What do you think is causing this? Thanks:)

  8. I tripped a breaker somewhere in my house while trying to plug in a George Foreman Grill. Now both exhaust fans in my bathrooms no longer come on. I looked at the breaker box and everything is in the right position. How do I get these back on?

  9. We have two bathrooms and neither had bathroom fans. About 2 months ago we had them installed. The installer used a fan that is up in the attic and the cover we see in the bathroom looks like an AC register. Two issues I have are: 1) on hot days the bathroom ac vents build up with condensation and 2) I smell the attic air and my entire house has had a cold and congestion since the install (about 2 months). Could the fans be installed incorrectly and causing us to become sick?

  10. Tim, I have a great exhaust fan I just installed in my bathroom. I had planned to vent straight up through my attic and out the roof. However, I discovered that I have a slate roof overlaid with a layer of asphalt shingles. I have never worked with slate before, and am uncertain I can seal up whatever hole I create for the roof cap. My house is brick. There are no gable ends or roof peaks near the fan that I could route the ductwork to. It would be too far away.

    Do you have any suggestions?

    • What? Someone nailed asphalt over slate? I can't believe that..... If it's true, it makes no difference. The flashing for the fan laces into the asphalt shingles. Did you watch my Bathroom Vent Flashing Video? If not, do it and you'll see how easy it is. If indeed there is slate under the asphalt, you just chip it out of the way. I'd LOVE to see a photo of this slate under asphalt. It had to be installed by the world's most idiotic roofer.

  11. These inline exhaust fans work very well partially because they use a high velocity reverse curve blower wheel. My only issue with using one for a bath is a large quantity of dust and lint will accumulate on the blower wheel and in the housing over a short period of time and will eventually need to be cleared out. I generally clean my two Broan s-110 , wheel and housings twice annually. The high humidity from showering helps lint- dust accumulate on these parts . Also once a year I venture up to the roof to clear a tiny accumulation of lint-dust from the 1/4 inch screen in the termination goosenecks (not doing this would render them completely clogged after 5-6 years of regular use). As well , I always use light gauge galvanized rigid duct .Try to go two pipe diameters before changing direction off the discharge ,then wrap with 2.5 inches of foilback fibreglass. Rigid duct provides far better air flow than flex, and as long as the entire duct is wrapped with sufficient insulation there should be no issues with condensation. The Broan s-110 is a traditional ceiling mounted exhaust fan which is fairly quiet and moves a sufficient amount of air given it is vented properly.

  12. Tim, I would like to know how to properly vent my downstairs bathroom. This bathroom has no window due to a den built on this once outside wall. This house is a Colonial style house built in the early 50's, well constructed exterior walls of cinder block & brick. I thought I had an exhaust fan, but I'm learning it's a fan/heater/light on a timer.

    • Jeannie, well, it's pretty straight forward. You need to figure out how to get a 4-inch metal vent pipe from the fan location to the closest outside wall.

      Then you do the required work to extend the pipe and put on the correct vent hood on the outside wall. I wish I could tell you more, but I'd have to be there and see what's going on.

  13. Tim doing a remodel in bathroom on second floor and below in first floor is a half bath with exhaust fan they put vent pipe behind tub on second floor do they make a charcoal filter to pipe this in and leave in the cieling of first floor thanks for any help or suggestions

  14. I have to reroute the vent pipe putting shower pan in and it is in the way on second floor. I can't route the vent outside due to not having access behind the ceiling since it is only for gases only thought I could leave it in ceiling hooked to a filter

  15. Tim-

    My wife and I have a small bath upstairs w a shower, sink, toilet in our 1930s home. It is our primary bathroom. There is a double hung window in the bathroom. We want to ventilate the bathroom w the door closed ( currently we shower w the door open). The window open technique is hot in the summer and very cold in winter! Our attic can't be used as we have vermiculite insulation (asbestos). We are at a loss of how to control the bathroom moisture. Dehumidifer? Any help is appreciated.

    • Grant,

      I believe this column shows you exactly what to do. Put in a great fan and exhaust it through the roof. If there is a 1/2-inch gap UNDER the door so it's not tight to the floor, that's plenty of space to provide the needed make-up air. READ all my other past columns about how to STOP MOLD in bathrooms.

  16. Who do I call to install a bathroom exhaust fan - an electrician or HVAC? I have a heat lamp in the area now which I want to have removed and replaced with an exhaust fan. Since there is already wiring in that area, I'm thinking just a HVAC guy is needed? I had an electrician come in for an estimate for tge entire installation and he was talking about venting to my soffits and now I read here that that is a bad idea! So confused as to WHICH trade to contact.

    • Cheryl,

      You really need FOUR trades - or a great cross-trained pro like I am.

      You need someone who knows about electricity, ducting, roofing, and drywall repair.

      I have a series of FOUR videos that show you how to find the PRO in your city or town in just about an hour.

      You need to get one of my Indoor Projects Contractor Hiring Guides. The videos are in there.

      You'll be amazed at how easy it is to locate this cross-trained PRO!

  17. I need to ensure my bathroom fans are vented to the outside and not the attic, and I need 2 new bathroom fans installed. Can you recommend a list of your cross trained pro in Toronto, Ontario, Canada?

  18. Attn Robert Burns and anyone else reading this article and the associated comments. Mr. Burns asked about whether it would be okay to terminate a vent inside a ceiling. The answer is NO, never!

    This would hold true whether it's a bathroom vent or a drain stack vent. A bathroom vent would trap moist air inside the ceiling space and lead to mold and potential lumber rotting issues, not good!!

    I think Mr Burns was asking about a drain stack vent because he mentions "since it is only for gases only". A drain stack vent terminated this way would trap deadly methane gases in the ceiling space leading to a very dangerous and potentially deadly situation. A drain stack vent should ALWAYS be terminated outside the house on the roof. I certainly hope Mr. Roberts modified his upstairs bath remodel project to accommodate the critical vent stack from the lower bath in the proper way.

    I am surprised Tim Carter missed commenting on this one. He needs a better system of website followup to an otherwise great website with tons of great information. NOTE FROM TIM CARTER - Read my response to this BELOW.

    The comment about asphalt over slate shingles was another classic. Completely incompetent roofer.

    • Why would you be surprised about me missing a comment? It was the day before New Years Eve. Here are some facts:

      How many pages are on this website? Close to 4,000 that have comments running on them.

      How many comments come in a day? Oh, about 100 or more.

      How long does it take to read all those comments and reply intelligently to all of them? At least five minutes EACH on average.

      How much time is that total each day seven days a week? Oh, it's just 8.33 hours per day - EVERY DAY.

      How can you run a business if you spend over eight hours each day answering one-off questions for people Tim? You can't. It's impossible.

      Why do some people offer harsh criticism about shortcomings? My guess is because it's easy to criticize and it's hard to start your own website where you can do what you feel OTHERS should do. I think it's similar to the mentality of many people who offer suggestions at meetings but want OTHERS to implement and carry out their ideas.

      Could Mr. Burns received an in-depth answer from you about his venting problem? You bet. I call people EVERY DAY on the phone and solve their problems. The trouble is, many are TOO CHEAP to invest in this service.

      CLICK HERE to have me call you on the phone.

  19. Tim Carter, I am positive that I speak for everyone that uses your website, we truly appreciate your advice on all subjects! With your guidance through this website you have helped me numerous times.

  20. Hi,

    I have a large bathroom that has a mold problem. I have replaced the original small fan with a large exhaust fan sized to accommodate the size of the bathroom but this has not solved the problem. i believe the problem is with the placement of the fan with relation to the shower and would like to know if it would be better to install a second fan close to the shower or move the existing one?

  21. We just purchased a modular last August. We started smelling mold a few weeks ago in our bathroom. The modular company offers a year warranty so they came to find out what's causing it. They found mold between ceiling and Attic floor where the exhaust fan is. There are several holes in the exhaust fan that aren't sealed. I think that's allowing moisture into the ceiling but they're trying to tell me those holes are suppose to be there from the manufacturer of exhaust fan. Is that correct?

  22. Hi Tim,

    Can you share what is the make and model of the exhaust fan shown in the picture above during the conversation with Faith ("the exact fan you are looking for is available. It has been around for years,..").

    Thank you,

  23. Our bathroom vent fans that are over our toilets seem to be letting hot air seep into the bathroom causing condensation and then mold on the bathroom ceilings. It only happens when it's really hot outside usually mid-June through mid-September. The vent fans are vented to the roof. We don't have a problem with the vent over our shower doing this. We have had our builder look at the problem and he had several other people look at the problem and basically they said we keep it too cold in our house (67 deg.) and that's why it does that. I know people that keep the temp colder than that in their homes and they don't have this problem. We are at our wits end with this problem. We had the house built and moved in May 2014. We have had this problem every summer. The builder had someone come and put more insulation on the attic floor over the bathrooms at the end of last summer, but this has not solved the problem because it has started again this summer. The builder says there's nothing else he can do. Any suggestions?

  24. We have two bathrooms side by side on our second floor. They both have the same exact layout (about 6'x7'). Both have their own separate exhaust fans (Nutone, 80CFM, 1.6amps), but share the same vent to the roof through a Y-shaped connector and flex 4" pipe. When we take steamy showers in bathroom A, paint from the ceiling of bathroom B is showing signs of moisture and paint is peeling in one area of the ceiling. We even noticed some condensation on the tile wall of bathroom B.

    What could be causing the problem in bathroom B and how can we fix it?

  25. To vent our bathroom fan, rather than cutting a new roof cap, could I use an existing unused double wall furnace vent pipe that extends through the roof and has the original furnace cap? We moved our furnace to the attic, and had a new vent placed, leaving the old pipe in place through the roof but disconnected about 2 feet into attic. Would I be able to connect 4 inch round or aluminum flex to this extension and have a decent vent?

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