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.
Is Your Bathroom Properly Ventilated?
Published November 26th, 2012 10:11 PM
2 of 26 comments
Hamtil Construction LLC on Apr 28, 2014Hi 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, one thing to keep in mind, is that a vertical pipe can sometimes leak condensation back downward (steamy shower, cold air in the walls/ attic). If you must do it this way, be sure to insulate the pipe, at least in the attic space. Definitely need to saw the door bottom too! Best of luck.