Why does my bathroom mirror still fog up when the exhaust fan is running?
An exhaust fan can pass basic airflow tests while still being entirely underpowered for the volume of steam produced by a hot shower. This leaves the mirror fogged, causes water to drip heavily from the ceiling and walls, and creates lingering humidity that risks causing lasting damage to the room.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
Why does my bathroom mirror still fog up when the exhaust fan is running?
- 1Buying a higher CFM exhaust fanDid this help you?
- 2Installing a timer switchDid this help you?
- 3Checking duct size, static pressure, and duct runsDid this help you?
- 4Leaving the bathroom door open to increase airflowDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“Trying to find the best bathroom exhaust fan for a small bathroom because mine technically works, but a hot shower still turns the mirror and half the room into a cloud.”source ↗
“It passes the basic toilet paper test and is definitely pulling some air, but apparently that doesn't necessarily mean the bathroom ventilation is actually keeping up with the amount of steam coming from the shower head.”source ↗
“It introduced severe humidity issues. The fan drips, the ceiling drips, the walls have long drip lines than can run to the floor, the mirror stays foggy for so long and we are afraid it's caused damage to our bathroom.”source ↗
Where this came up
People with this problem also raised
- 6Why is my bathroom exhaust fan making a strange noise?
- 3How to clear heavy bathroom steam without an exhaust fan
- 2Dust blowing out of AC vents
- 5Why does my bathroom stay humid even with the fan on?
- 5How to clean a bathroom mirror without ruining the coating
- 2Air coming out of dryer when bathroom fan is on