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Bath Fan: Inside Shower vs. Outside Shower

qofmiwok | Posted in General Questions on

Zehnder recommended putting my exhaust fans right outside the shower.  I’ve heard about 50/50 on this.  What are the pros and cons of putting the fan inside the shower vs right outside the shower?

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  1. BirchwoodBill | | #1

    Depends on the geometry and size of the room and your ventilation goals. The advantage of placing in the shower is that you exhaust more humid air, so it does not get into the roof assemble. That is for a traditional bath exhaust such as an Aldes or Panasonic unit.

    For an ERV application, they may want to run the fan continuously, so you place it for more unrestricted air flow. It also depends on the source of your makeup air for a balanced airflow.

    The placement also needs to consider the overall effective length of the duct, the more bends the more resistance.

  2. graham78 | | #2

    Some manufacturers will require the fan to be GFCI protected if less than 5' to the shower head.

  3. Expert Member
    Akos | | #3

    Well insulated houses tend to have much warmer walls which reduces the chance of condensation and mold from running a shower. Provided it is not a steam shower, this gives you much more flexibility of where to place the bath fan. Anywhere in the room will work.

    I prefer to place it above the toilet as it does a much better job there containing the more problematic air pollution.

  4. Expert Member
    BILL WICHERS | | #4

    Don't put the fan inside the shower. I'm not sure any are actually rated to be used like that. Lights inside showers need to be rated for the purpose, due to the moisture, and I don't think there are any fans with a similar rating.

    I would put the fan outside of the shower, and I like Akos' suggestion for putting it over the toilet :-)

    Use of a time delay switch that keeps the fan running for a while with auto-shutoff at some time later is a nice feature too. This makes it easy to run the fan to get the moist air out, without the worry of forgetting to turn it off after leaving the bathroom.


    1. user-5946022 | | #11

      Even better, run it on a condensation module so it turns on and off automatically based on moisture.

    2. Moderate | | #12

      Many fans are rated to be used like that. Panasonic fans are UL listed for tub and shower enclosures. Of course, just like lights would be, fans installed in a tub or shower enclosure must be connected to a GFCI (Ground Fault Circuit Interrupter) - protected branch circuit.

  5. andy_ | | #5

    Can you clarify if you're talking about placement of stale air intakes for a central Zehnder HRV or a bath fan unit that will have a fan in the bathroom ceiling?
    I think you're getting advice here for two different things.

  6. qofmiwok | | #6

    The Zehnder exhaust has a booster switch in the baths and takes the place of bath fan unit. I guess I shouldn't technically call it a fan; it's a port back to the Zehnder unit. (However I am interested in the answer either way.)

  7. Expert Member
    Akos | | #7

    To clear a bathroom you need at least 50CFM flow. You generally want around 65CFM stale air pickup in the kitchen which doesn't leave a lot of extra flow. A typical residential HRV would have enough extra capacity to exhaust one maybe two bathrooms.

    Best is to install the HRV pickup in the bathrooms most commonly used and run a standard exhaust fan for the rest.

  8. coolviper777 | | #8

    Personally, if you are building/designing a house, for the master bath, you should have a separate cubicle/room off the main master bath for the toilet, with it's own vent fan. And a separate fan for the main area of the master bath.

    For a normal bath, just put it in the middle, or wherever it's convenient, as most baths aren't that big. Go with a 100CFM model for any normal sized bath. 50CFM is really too small, and will run forever, and won't really work well for bad smells. The 100CFM unit I had barely kept up various guest bad smells when they visited, I couldn't imagine having a 50CFM unit. And on the plus side, the 100CFM made short work on humidity after a shower also.

  9. Expert Member
    BILL WICHERS | | #9

    If you're going to be inspected, a higher than needed CFM rating will help to overpower any duct losses to ensure you still pass inspection -- if they actually test for airflow. I've heard of people failing before because duct back pressure reduced the fan's airflow too much.


  10. WilliamBishopi | | #10

    Installing the fan outside the shower is the best option for me. In case you install the fan inside the shower, you always risk, in my opinion, this risk is not worth it, for the proper designing options of outside fans you can look at this article to learn more about kitchen, living room and stuff like this. If you will get other questions regarding the topic, feel free to reach me via private message or answer me directly on this topic, have a good one, qofmiwok!

  11. rockies63 | | #13

    What are the chances that on the very day someone asks a question about “where they should place their bathroom fan” a video is uploaded to Youtube that answers that very question?

    This video was made by Corbett Lunsford, who runs the Home Performance channel and is co-host of the PBS television show Home Diagnosis TV. His company specializes in analyzing how reactions can occur between all the chemicals, pollutants (and their byproducts) within your home and how to reduce or eliminate them. One of the main subjects he focuses on is ventilation, not only by using whole house units but also through kitchen hoods and bath fans.

    The main question with bath fans is deciding on why they are there. Are they there to ventilate odors, ventilate moisture, or to help facilitate a constantly moving stream of fresh air through the room? He says their primary function is to remove moisture, not odors, and therefore the bath fan should be located in the ceiling above the tub and shower. After all, that’s where the moisture is being created.

  12. jberks | | #14

    I'm a fan of Corbett, he's the right kind of crazy for this kind of work.

    My personal opinion is to have the fan in the shower, moisture does the most damage, get it out.

    However, I'm all about being optimal in design. So with that, Forget about the typical noisy squirrel cage ceiling fan. Have an inline fan, or an exterior wall mounted fan and have the suction duct split, one within the shower, the other down low behind the toilet, or if you have a seperate toilet room which is preferable, then the suction location doesn't matter as much in the toilet room. You get both airborne issues out and its quieter. inline fans are usually more efficient can pull more cfm or can be variably controlled.

    I'd rather put a dedicated HRV in the bathroom if I had the roof, but it's hard to design for when they are usually 3-4x the cost & 3-4x less airflow of a good inline fan.

    Btw, It's 2022, I think by now toilets should have suction integrated within them by now. Kind of like the Aussie fantech Odourvac (yes, google it). We have toilet seats singing songs to us now and having light shows and stuff.... Let's get it together toilet designers! Ventilation is important.


    1. Expert Member
      MALCOLM TAYLOR | | #15


      I wonder if you wouldn't get the best of both worlds by situating the fan just outside the shower enclosure? It would be able to pick up all the moisture trying to escape, while not being right in the wet-zone, and would be closer to the toilet when you wanted that horizontal airflow for odours.

      1. jberks | | #17

        Hi Malcolm,

        Yes if you are going with the standard ceiling fan. I agree having it in the between the shower and toilet fits best for both extrication uses.

        Yes, bath fans are totally dependent on the scenario of the house, what the people want, cost, if there is room for remote mechanicals etc.

        Basically I'm just pointing out that a better system could be built if you go with a remote inline fan. Without that much more cost. You can get higher cfm blowers, quieter operation, and place multiple suction points directly at the use locations without having to consider being in the wet zone, or being too far away from the toilet etc.

        Consider the fantech prioair 6. Although its a $250 6" blower, for the price, performance, energy consumption, low noise and it's compact form, I like them.

        Just my opinion on bath ventilation. I never would have thought I'd be so opinionated on such a subject.


  13. rockies63 | | #16

    Malcolm, that's what the hotel did in the video and it didn't work.

    1. Expert Member
      MALCOLM TAYLOR | | #18


      isn't that the fan on the wall around the corner? I'm suggesting placing it on the ceiling just outside the curtain or glass.

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