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Is Your Bathroom Properly Ventilated?

We've seen it probably more than 100 times. In an attic, the bath fan discharges directly into a pile of insulation. You would be surprised that it's more common than many people realize! If you don't know the condition of yours, it's worth a quick investigation. So, what are the indicators of a properly ventilated bathroom? Here are a few tips.

1. Select the correct size bath fan. Many have a square footage chart included at time of purchase, but there are tables available online as well, such as this one from HVI:

2. Ensure adequate make up air can reach the fan. As pictured, allow a minimum of 3/4" clearance under the door, and even more if possible. Use caution, however, that hollow doors only have a small solid rail at the bottom which could limit the cut off.

3. Always terminate the ductwork to the home exterior. In the photo, the duct is attached to a pre-cut galvanized sheet, and connected with a 4" starter collar. It is attached directly under a roof static vent which was installed solely for this purpose.

4. How long to allow a fan to run post-showering? The Home Ventilating Institute recommends that a fan should be left on for 20 minutes after a shower to thoroughly clear humidity and to ensure moisture and condensation in the fan body or ducting is minimized. A preset timer, such as illustrated in the attached photo, helps achive this.

5. Not sure if your fan is drawing air? As pictured, you can give it a quick (albeit not scientific) test using a sheet of paper. if your fan is blocked by insulation, the paper likely will not stick.

Got a question about this project?

  • Cherie Dunkel-Hoysock
    Cherie Dunkel-Hoysock Pottsville, PA

    Hamtil Construction LLC, yes we literally share a sewer. The homes were built in 1896 and it was a family who built them side by side. So the sewer is shared from the second floor bathroom all throughout the house and then the actual pipe starts

  • Becky (J) P
    Becky (J) P Highland, IL

    @Hamtil Construction LLC, well you don't really live that far away from me! Will keep you in mind should we decide to ever do it. (I have declared 2013 as a no home improvement year, lol)

  • Kristine
    Kristine Tullahoma, TN

    My 77'sq ft first floor bathroom was just retiled and now I only have 1/4" clearance below the door! This bathroom on the first floor lies directly below the 2nd floor bathroom. Both are getting new vent fans and will be tied in to the same vent pipe

    • Woodbridge Environmental Tiptophouse.com

      @Kristine The cfm will be determined by the size of the room itself. As far as the door bottom opening, of course larger is better, but you can determine if it needs to be enlarged by using toilet paper on the fan. If the paper stays on the fan after

  • Hamtil Construction LLC
    Hamtil Construction LLC Saint Louis, MO

    Hi Khol, thanks for the comment. I would suggest an 80cfm fan. Definitely wise to terminate to the exterior. I would try to keep the ducts separate if possible, just so you do not lose airflow, but I understand that it's not always possible. Also,

  • Hamtil Construction LLC
    Hamtil Construction LLC Saint Louis, MO

    Hi @Cherie Dunkel-Hoysock - I am just revisiting this thread, saw your comments, and I was curious if you ever resolved your sewer/ vent issue?

Inspired? Will you try this project? Let the author know!