Bathroom Fans for Home Health

Keep them humming for home health

Bathroom Fans

When your bathroom mirror fogs up after a shower, it’s more than a personal grooming challenge. It’s a reminder to turn on the fan. You say it’s already on, and there’s still fog? Then it probably isn’t big enough to protect your bathroom from the ravages of moisture. In the long run, a fan is your most potent tool in keeping your bathroom from developing the mold and rot that, if left unchecked, can be your bathroom’s downfall.

Bathroom fans send damp air outdoors. They can be installed in outside walls and vented directly outside or, using ducts, in a ceiling. To do their job well, they need to be the right size for your bathroom. If your fan is too small, it won’t expel enough humid air. If it’s bigger than necessary, it will waste money and energy.

Top Tips

At home

  • Leave fans on for 20 minutes after use of the bath or shower. You may want to use a timer. But don’t leave them on any longer than this, especially in the winter, because they will move warm air out of the house.

When shopping, look for

  • Certification from the Home Ventilating Institute. This trade organization’s seal of approval ensures that the fan’s air-volume and sound ratings are reliable.
  • Energy Stars. Energy Star label products use up to 70% less energy than others.
  • Cubic feet per minute. For bathrooms with an area of 100 square feet or less, the fan should be rated to move 1 cubic foot of air per minute per square foot of floor space. So if the bathroom is 10 by 10 feet, you need a product that is rated to move 100 cubic feet of air per minute. If the bathroom is only 4 by 10 feet, you need 40-cubic-feet-per-minute. For bathrooms larger than 100 square feet, there are two approaches, depending on the configuration of the room, position of the walls, and ease of installing ducts. Option one is to install several fans: 1) a 50 cubic-foot-per-minute one in the shower or above the tub; 2) a 50 cubic-foot-per-minute one near the toilet; or 3) a 100 cubic-foot-per-minute one above a tub with jets or in a steam shower. Option two is to simply install one 150 cubic-feet-per-minute fan.
  • Sound rating. If you are sensitive to sound, check the rating for “sone,” which is the measurement for loudness. A typical bathroom fan is 3 or 4 sones. Energy Star products are 50% quieter than ones that haven’t earned this label.
  • Outlet size. If a duct is already installed, make sure the outlet size matches the size of the duct.
  • Combination ceiling light/fan. These will usually be simpler to install, especially if wiring is already in place and a duct can be installed without difficulty.
  • Positioning. Try for an outside wall, but if that’s not possible, install it on a wall or ceiling where it’s easy to add ducts to the outside.


…to you
Mold and other tiny organisms that grow in damp places can cause allergies, itchy eyes, runny noses, headaches, fatigue, and flu-like symptoms. A good fan makes your indoor air healthier.

…to your wallet
Energy Star products can save you $120 over the life of the fan. More importantly, they can save you the cost of repairing the rust, peeling paint, damaged wallboard, warped wood, loose or stained tile grout, and even structural damage that can occur in poorly ventilated bathrooms.

…to the Earth
The 70% less energy used by Energy Star products means less global warming gas and other pollutants are emitted into the air.

Common Mistakes

  • Faulty duct installation. If ducts are twisted or improperly attached, they can increase the noise level and leak moist air into the building.
  • Improper sealing. If the fan isn’t sealed to the wall or ceiling it won’t move the air as well, and cold air can leak in from the outside.

Getting Started

If you’re having an installation done by a handyman or contractor who is providing the fan, check for proper sizing.


  1. mary weenike May 11, 2010
  2. neil July 23, 2010
  3. apartment make ready October 23, 2011
  4. lbt nashua May 6, 2012

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