Bathroom exhaust fan general requirements

Bathroom vent improperly discharging into the soffit resulting in mold growthBathroom vent discharging into the soffit which is not recommendedEvery bathroom without an openable window (min 1.5sq. ft) requires an exhaust fan.

The bathroom ceiling exhaust (or wall) should be discharging to the house exterior, not into the ceiling / wall frame cavity, or another room, crawlspace, attic, etc. This is extremely important if your bathroom contains any significant humidity source like a shower stall, bathtub, steam shower, etc.

Bathroom vent improperly discharging into the atticDischarging moisture from your bathroom fan into some enclosed and/or poorly ventilated areas is often responsible for the crawlspace and attic mold growth. By the way, have you ever checked your attic ventilation?

  • Bathroom ceiling exhaust fan requires a damper to prevent back-drafts
  • Bathroom exhaust exterior vent opening should be screened with a ¼” to ½” mesh to prevent birds from building nests inside the vent pipe

GFCI protection for bathroom ceiling exhaust vent

Bathroom vent GFCI protection is required for installations above the shower or bathtubNEC (National Electrical Code) does not require bathroom exhaust fans to be installed on a GFCI protected circuit. However, you should be following the manufacturer’s installation instructions. In most, or should I say in all, cases concerning a bathroom exhaust fan installation directly above the bathtub and / or shower stall (or any other moisture sources), the bathroom fan must be listed as suitable for such locations and must be installed on a GFCI protected circuit.

This is a paragraph from the bathroom exhaust fan installation instructions:

“If this bathroom exhaust fan is to be installed over a tub or shower, it must be marked as appropriate for the application and be connected to a GFCI (Ground Fault Circuit Interrupter) protected branch circuit.

Bathroom vent - GFCI protection requirement for over the shower and tub installationsTo test if a bathroom exhaust fan is GFCI protected, turn the fan ON, and push TEST button on a bathroom GFCI receptacle or GFCI breaker dedicated for this bathroom. If the exhaust fan is still running after the receptacle or the breaker tripped, it is most likely not protected (there are occasionally some hidden GFCI receptacles installed).

Learn How to Install GFCI Receptacle

You should always check manufacturer tag before attempting to install a ceiling exhaust fan directly above the bathroom tub or shower stall.

Bathroom exhaust fan TIP

Bathroom vent - humidity sensing fan with time and sensitivity adjustmentFor those who always forget to turn ON the bathroom exhaust fan (or forget to turn it OFF), I highly recommend one with a humidity-sensing switch. I’ve been using two of those in my bathrooms for almost 4 years, and I am very happy with their performance. One of the humidity sensors failed during the first year, but manufacturer replaced it without any problems.

Bathroom humidity sensing fan (at least the one that I have is made by BROAN) can be wired like a 3-way switch – it means that you can turn the fan ON/OFF using a regular wall switch or it will be automatically activated by an elevated humidity level.

Controls on the bathroom humidity-sensing fan allow for the time of operation and humidity level adjustments.

Let me know if I’ve left anything unanswered about bathroom exhaust fan …

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