Size
Fans are rated in cubic feet per minute, or CFM. A common rule of thumb for bathrooms up to about 100 square feet is one CFM for each square foot of floor. Larger bathrooms are sized by their fixtures.
IllustrationIn short
A fan sized for the room, vented outdoors, and run long enough.
- Topic
- Bathrooms
- Published
- By
- Collaborative Construction
A new bathroom looks its best on the day it is finished. What keeps it that way in Southwest Florida is mostly invisible: how well the room gets rid of moisture after every shower.
Lighting and ventilation improvements are part of our bathroom remodeling services. This is what good ventilation looks like in a humid climate.
Key points
- In Florida, an open window often brings in air as humid as the air you want out.
- A common rule of thumb is one cubic foot per minute of fan capacity for each square foot of floor.
- A quiet fan is one that gets used.
- The duct should end outdoors, never in the attic.
- Run the fan for about 20 minutes after a shower. A timer or humidity switch does it for you.
Why it matters
Moisture has nowhere to go
In a dry climate, a damp bathroom dries on its own. Here, the air outside is often as humid as the air inside, so opening a window does little for much of the year.
Moisture that lingers shows up as mildew on grout and caulk, paint that peels, a door that sticks, and a vanity that swells at its edges. None of that is a tile problem. It is an air problem.
The fan
Choosing and placing it
Noise
Fan noise is rated in sones, and lower is quieter. A loud fan gets switched off early. A quiet one runs as long as it should.
Position
Close to the shower, where the steam is, and away from the door or supply vent that feeds fresh air in. A separate toilet room needs its own fan.
The duct
The duct should run to the outdoors through the roof or a wall. A fan that empties into the attic moves the moisture to a place where you cannot see the damage. Short, straight runs work best.
Controls
Make it automatic
The usual advice is to run the fan for about 20 minutes after a shower. Few people remember to.
A timer switch runs the fan for a set period and shuts it off. A humidity-sensing switch turns the fan on when the air gets damp and off when it clears. Either one costs little compared with the rest of a remodel and does more to protect it than almost any finish.
During a remodel
What a remodel changes
A larger, open walk-in shower lets more steam into the room than a tub behind a curtain did. A fan that was adequate before may not be afterwards.
A remodel is also the practical time to fix what is hidden. With the ceiling or walls open, an old fan can be replaced, a duct that stops in the attic can be extended outdoors, and a bathroom with no fan at all can get one.
Materials
Finishes that forgive
Ventilation does most of the work, and materials help. Porcelain tile absorbs very little water. A waterproof system behind the tile keeps moisture out of the wall. A vanity top without seams, paint made for bathrooms, and flexible sealant where surfaces meet all stand up better to a room that is wet every day.
Good to know
Common questions
01Does a bathroom with a window still need an exhaust fan in Florida?
In practice, yes. For much of the year the outdoor air is as humid as the air in the bathroom, so an open window removes little moisture. An exhaust fan vented outdoors does the job in any weather.
02Where should a bathroom fan vent to?
Outdoors, through the roof or an exterior wall. A fan that ends in the attic moves moisture into a space where it can cause damage out of sight.
03How long should I run the bathroom fan after a shower?
About 20 minutes is the usual advice. A timer switch or a humidity-sensing switch takes care of it without your having to remember.
Keep reading
Related pages
This article is general guidance for homeowners. Every home is different, and what suits yours is something to look at in person.
Planning a remodel?
Complete the form below or call us at (239) 295-8613 and one of our team members will be in touch to discuss your project and provide a free, no-obligation estimate.
Open form in a new tab Or call (239) 295-8613