The Truth About Your Bathroom Ventilation Fan

Most people, when they move into an apartment or new house, are perfectly happy when they flip that switch in the bathroom and the ventilation fan comes on.  “Whew!  It works.  One less thing we need to worry about.”  

Not so fast, though. Your bathroom ventilation fan might turn on when you flip the switch, but that doesn’t mean it’s working.

Bathroom exhaust fans are rated based on the volume of air they move.  For example, a fan rated at 100 CFM will move 100 cubic feet of air per minute.  A fan rated at 100 CFM would be ideal for a 100-square foot bathroom.  Generally, the higher the CFM rating, the more effective the fan.

However, the size of your bathroom isn’t your only concern.  If you happen to be lucky enough to have a bathroom larger than 100 square feet, you’ll need to consider each of the different fixtures in that room.  If it also has a shower, add 50 CFM.  A bathtub adds another 50 CFM, and a whirlpool tub adds an additional 100 CFM.

So, if your bathroom is larger than 100 sq. ft. and has a toilet and shower, you’ll need a fan with a rating of at least 100 CFM.  If it also has a whirlpool tub you’ll need one with a rating of 200 CFM.

What About Ventilation?

Most building codes these days require that your fan be attached to ductwork that allows the warm, moist air from your bathroom to be ventilated to the outside of your home.  This help alleviate mold and mildew, and also eliminates odors.

Unfortunately, especially in older homes, if you were to follow that ductwork through your attic you’d be in for a big surprise.  It twists and turns, over and under, and it’s usually constructed from a coiled hose, just like the ventilation hose on your dryer.

All those twists and turns and coils work to diminish the fan’s ventilation capability.  In fact, in worst case scenarios, the air literally stops moving before it reaches the end of the ductwork.  When that happens, the moisture condenses inside the ventilation hose and there’s actually a standing pool of water.

How Do You Know If Your Bathroom Fan Is Getting The Job Done?

Not sure if your bathroom ventilation fan is as effective as it should be?  If you mirror is always steamy and you have condensation on the walls, then chances are your fan isn’t getting the job done.  Try this simple test:

Turn the fan on and place a square or two of toilet paper on the fan.  If the fan has enough draw to hold the paper in place, then it’s probably powerful enough.  If not, then it’s time to replace your fan.

How To Choose A Bathroom Ventilation Fan

Choose a good quality fan:  Look for a fan rated with a noise-level of 2 or less.  A cheap fan will make more noise which means you’ll be less likely to use it.

Vent as close as possible:  Make the ventilation duct as short as possible, in a straight, direct line to the outside.  Stretch coils tight to eliminate as much friction as possible.  If you must extend the duct work make sure you make allowances and purchase a fan with a higher CFM rating.

Insulate duct:  Insulate the duct work where it passes through open spices, such as your attic or soffit or walls.  Otherwise, condensation could collect on the duct and drip down onto the ceiling.

Control switch:  Most people turn their ventilation fan off as they exit the bathroom but that’s too soon. If you have a smaller bathroom and you shower with the door shut your fan probably won’t even start pulling out the warm, moist air until you open the door.  Your ventilation fan should be allowed to run for at least 30 minutes.  Use a timer switch instead of a standard on-off switch to ensure the steam and smells are fully eliminated from your bathroom.

One thought on “The Truth About Your Bathroom Ventilation Fan

  1. I broke the plastic eyes that hold the springs to hold fan cover, then I lost one of the springs. Do you know if it is possible to purchase replacement covers for exhaust fans?

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