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.

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      • Becky (J) P
        Becky (J) P Highland, IL
        on Nov 27, 2012

        my bathroom fan is only ventilated to the attic. I never understood why you would want moistness sitting around up in the insulation. We did get a new roof last year and I questioned the roofer about ventilating it to the roof, but he didn't seem too interested.

        • Douglas Hunt
          Douglas Hunt New Smyrna Beach, FL
          on Nov 27, 2012

          I love the preset timers for fans. A friend has one and that is definitely what I will do in the future.