Don’t Want Mold Gremlins? Make Sure Your Bathroom Ventilation Sucks.

Raise your hand if you like moldy fog? Unless you’re the Toxic Avenger you didn’t raise your hand. I want to make sure you understand the importance of why your bathroom ventilation needs to suck. Let me explain what I’m talking about.

What Bathroom Ventilation Is and What It Does

Bathroom exhaust fans are designed to remove odors and moisture from the bathroom to the outdoors. The ventilation ducts usually terminate at the roof but some exit in a side wall of the home. The important thing to remember is that your ventilation ducts should terminate to the outdoors.

Here’s why this is important: moisture can build up in a bathroom when you start a hot shower or bath. If the moisture isn’t removed properly it can lead to mold and fungi growth. That’s bad. Very bad.

The ingredients that mold and fungi need to throw a mold spore party:

  1. oxygen
  2. temperatures between 45 – 85 degrees
  3. a food source such as wood or paper (found in sheet rock)
  4. moisture

Believe me, this is the kind of party you DON’T want to be a part of. This party isn’t a good time. It actually creates a very bad time. Remember that 80’s movie “Gremlins?” You get a mogwai wet then they reproduce into a lot more mogwais. You feed a mogwai after midnight then they turn into menacing, blood thirtsy gremlins. To ensure you don’t spawn your own mold gremlins make sure your bathroom ventilation works properly.

During inspections, I have found attic exhaust terminating in attics and crawl spaces. Sometimes this was done intentionally because the ducts ended in these areas and unintentionally because the ducts had exterior exits but were broken or cut.

This allowed the air to exit in the crawl space or attic.

Bathroom duct exiting into attic.

Bathroom duct exiting into attic.


It’s also important that the ducts terminate outside. Also, you’ll need to make sure the ducts have a damper door that prevents pests and unconditioned air from entering the duct when the fan is off. The damper door should open when the fan is on and close when it’s off.

How can you tell if your fan’s exhaust is working properly…it Sucks

Right now you’re saying, “That’s a bad thing, right?” Let me explain. Just because you may hear the motor doesn’t necessarily mean that it’s removing air from your bathroom. Here’s how to tell if your bathroom ventilation is working properly. Hold a piece of tissue paper near the fan fixture and see if it sucks the paper up to the fixture. If it sucks, then your fan is pulling air out. If it blows it away, then your duct may be clogged or there could be a problem with your damper door. If the fan fixture and small fans are clogged with dust this prevents air from being sucked out efficiently, and should be cleaned.

Getting moisture out of the bathroom is important and to the end it’s important to keep the fan running after you have finished your bath or shower. Some fans can be installed with a timer that will automatically shut off after an allotted time period.

I leave you with this, a bathroom ventilation fan should be connected to a duct capable of removing moisture vapor and odors to the outdoors. To ensure you do not spawn your own mold gremlins in your bathroom make sure your bathroom ventilation sucks (that’s a good thing). Mold or fungal growth within the bathroom or attic is an indication of improper ventilation that must be corrected in order to avoid structural decay of the home and respiratory health issues.