Bathrooms 03.22.14

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

22 Comments Displaying 15 of 22 comments | See Previous
  • Sharron W Memphis, TN
    Hamtil Construction LLC This is SUCH great information! Our house is so old and I am confident that the bathroom fan is not properly vented....the Master Bath doesn't even have a
  • Cherie Dunkel-Hoysock Pottsville, PA
    I am currently remodeling my home that is attached to my neighbors. I do not have ventilation and plan on installing one. However, we share a sewer and everytime my neighbors flush their toilet I lose my water in my toilet and it always smells like
  • Peter Klarman Bayside, NY
    When my first floor and basement bathrooms were renovated the first task was to vent the first through the roof and the basement through the brick wall.
  • Erin H Las Vegas, NV
    I learned that trick from Mike Holmes and none of my bathrooms are properly ventilated. They don't really take pride in the housebuilding anymore. The developers just want to crank out as many houses as possible to make a bunch of money. My house is less
  • Hamtil Construction LLC Saint Louis, MO
    Becky J Well, it's not really a good idea to have it discharging into the attic. Code requirements for us dictate that it must terminate to the exterior, and that is the ideal way to do it. If
  • Hamtil Construction LLC Saint Louis, MO
    Thanks for the feedback Building Moxie, and I have read that post by Sean, which is a good one on the topic!
  • Hamtil Construction LLC Saint Louis, MO
    Barbara Kalyta Sorry to hear about the issue. To me, it sounds as though you may have a plumbing vent issue, which is separate from a bathroom fan vent. While a vent fan may help with the
  • Vicki Smyrna, GA
    ty for sharing. we learned from weatherization that it should go out of the house, not to the attic. we have timer to turn one hour before we go to shower. we are thinking to have humidity sensor bathroom fan exhausted to turn on by itself whenever there
  • Hamtil Construction LLC Saint Louis, MO
    Sharron W Thanks for the feedback! Interestingly, building code in many places states that you can forgo the bath fan if there is fresh air in the room, i.e. from a window, and that it is
  • Vicki Smyrna, GA
    they from weatherization used incense to test but paper is very good idea. they put duct from bathroom ceiling toward to eave instead of to the attic.
  • Hamtil Construction LLC Saint Louis, MO
    Cherie Dunkel-Hoysock That is a new one for me. You mean that you share a sewer lateral in the yard out to the main sewer line? Is it undersized? Have you had a drain inspector run a
  • Hamtil Construction LLC Saint Louis, MO
    Good tips Vicki and thanks for adding to the discussion. The smoke test for fans is a good one, and I would say is more reliable, especially when checking the make up air under the door. I
  • Building Moxie Baltimore, MD
    thanks Paul @ Hamtil Construction LLC it did get me thinking ... excellent tip on looking at swapping out only the motor. I'll look into it. cheers my friend.
  • 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 coming
  • Becky J Troy, 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)
  • Likes

    Liz C Sharon Bothwell Garage Designs of St Louis Vicki Building Moxie Yair Spolter Marilyn A Patti S Photokricket Lauren Little Lindalumoore