Quick test: if your mirror stays foggy, your fan is losing
If you take a shower and the mirror stays fogged for 20 minutes, your fan is not keeping up. And when a fan can’t move moisture out, your bathroom turns into a tiny indoor rainforest. Mold loves that.
- Quick test: if your mirror stays foggy, your fan is losing
- Step 1: Do the tissue test
- Step 2: Clean the grille and the crud you can’t see
- Step 3: Check the vent path, not just the fan
- Step 4: Make the fan automatic so humans stop “forgetting”
- Step 5: If your fan is just weak, upgrade smart
- Step 6: Stop feeding bathroom mold
- FAQs
Step 1: Do the tissue test
Turn the fan on. Hold a single square of toilet paper or a tissue up to the fan grille.
- If it sticks: airflow exists
- If it falls: airflow is weak or blocked
Step 2: Clean the grille and the crud you can’t see
Most bathroom fans are basically dust magnets. Pop the grille off and clean it. Then vacuum the fan housing as much as you can reach.
This alone can improve airflow noticeably, especially if it’s been years. (No shame, nobody puts “vacuum bathroom fan” on their vision board.)
Step 3: Check the vent path, not just the fan
A fan can be fine but the ducting is crushed, clogged, or dumping into the attic (which is a whole other mess).
Clues your vent path is the problem:
- Fan sounds loud but doesn’t clear steam
- Dust keeps raining from the grille
- Mildew keeps showing up even when you clean
Step 4: Make the fan automatic so humans stop “forgetting”
This is the fix that feels like cheating. Add a humidity sensor switch so the fan turns on when humidity spikes and shuts off after things dry.
Leviton humidity sensor switch example:
It’s also a money saver because it prevents the “fan runs for 4 hours because someone left it on” situation.
energy bill reset easy cuts that work
Step 5: If your fan is just weak, upgrade smart
If you’re upgrading, look for:
- Low sones (quiet, so people actually use it)
- Proper CFM for your bathroom size
- Reliable brand with easy install access
Example Broan-NuTone LED exhaust fan listing:
Step 6: Stop feeding bathroom mold
Even with a good fan, you still need basic moisture habits:
- Squeegee shower walls if your bathroom stays damp
- Hang wet towels so they actually dry
- Leave the door cracked after showers if the room traps steam
how to get rid of mold in house complete guide
FAQs
How long should a bathroom fan run after a shower?
Usually 20 to 30 minutes. A humidity switch makes this automatic.
Why does my fan run but the bathroom stays humid?
Dirty grille, blocked duct, or the fan is underpowered for the space.
Can a weak bathroom fan increase mold risk?
Yes. Persistent humidity is one of the biggest mold triggers in homes.
Do humidity switches really work?
Yes, especially for households where people forget to turn fans on.
