Bathroom Exhaust Fan

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Bathroom Exhaust Fan

Why do I need a bathroom exhaust fan?  I already have a window in my bathroom!  Bathrooms must have an exhaust fan regardless of a window.  Prior to 2013, a bathroom could have a window or an exhaust fan.  Today, however, a residential bathroom must have a window and an exhaust fan.

There is no grandfathering allowed.  If your bathroom does not have an exhaust fan, you must install one when you remodel your bathroom.  There are few exceptions.

Why is a bathroom exhaust fan required?

California Building CodeIt is the law.  The California Building Standards Code, California Code of Regulations makes this clear.  Title 24, Part II, Chapter 4, Residential Mandatory Measures, Indoor Air Quality and Exhaust, Section 4.506.1, Bathroom Exhaust Fans states:

Each bathroom shall be mechanically ventilated and shall comply with the following:

  1. Bathroom Exhaust Fan | California Building Code RequirementsFans shall be ENERGY STAR compliant and be ducted to terminate outside the building.
  2. Unless functioning as a component of a whole house ventilation system, fans must be controlled by a humidity control.
    1. Humidity controls shall be capable of adjustment between a relative humidity range of ≤ 50 percent to a maximum of 80 percent. A humidity control may utilize manual or automatic means of adjustment.
    2. A humidity control may be a separate component to the exhaust fan and is not required to be integral (i.e., built-in).


  1. For the purposes of this section, a bathroom is a room which contains a bathtub, shower, or tub/shower combination.
  2. Lighting integral to bathroom exhaust fans shall comply with the California Energy Code.

Do I really need a bathroom exhaust fan if I have a window?

Mold in Bathroom - Bathroom Exhaust FanThe short answer is “Yes”!  More than 90% of the bathrooms I look at have visible moisture and/or water damage.  Almost all these bathrooms have at least one window.  How can this be?  Most folks only open the bathroom window in the hotter summer months.  During the cooler fall and winter months, the window stays closed or is only open a crack.  Those wonderful hot showers that feel so good and relaxing generate a lot of steam and moisture.  Here is where the trouble starts.

California Residential Code, Section R303.3.1 Bathroom exhaust fans, specifically states the following:  “Each bathroom containing a bathtub, shower or tub/shower combination shall be mechanically ventilated for purposes of humidity control in accordance with the California Mechanical Code.  Window operation is not a permissible method of providing bathroom exhaust for humidity control.”

All that moisture condenses on the ceilings, walls, baseboards, cabinets, toiletries, flooring, etc.  Mildew (mold in early stage) and molds grow on wood and paper products.  It also grows on wallpaper, carpets, vinyl flooring, drywall, grout, fabric, insulation, and other organic materials.  Mold growths, or colonies, can start to grow on a damp surface within 24 to 48 hours.  Mold continues growing and destroying until steps are taken to eliminate the source of moisture.

In addition to the damage molds can cause in your home, it can also cause mild to severe health problems.

Are there any adverse health problems due to mold?

Mold under Floor - Bathroom Exhaust FanInfants, children, immune compromised people, pregnant women, individuals with existing respiratory conditions, and the elderly are at higher risks for adverse health effects from mold.  When timely drying out does not have a chance to occur, that is when trouble starts.  Mold hides in areas such as under flooring (carpet, vinyl, Pergo®, laminates, etc.) and behind walls and ceilings.

Typical symptoms reported from mold exposure include:

  • Respiratory problems – wheezing, asthma attacks, etc.
  • Nasal and sinus congestion or dry, hacking cough
  • Eye irritation – burning, watery, redness
  • Nose or throat irritation – sneezing fits, bloody noses
  • Skin irritations – rashes or hives
  • Nervous system – headaches, memory loss, mood changes
  • Aches and pains

What kind of fan do I need?

There are lots to choose from.  Bathroom exhaust fans offer built-in lights, nightlights, heaters, motion sensors, and humidistats.  In my over 45 years of bathroom remodeling, I believe Panasonic® makes the best bathroom exhaust fan.  They are the most durable, highest quality, most efficient, and quietest bathroom exhaust fan on the market today.  They are completely California Title 24 and Energy Star compliant.  Most importantly, they work for decades removing harmful and unclean air and moisture.

Bathroom Exhaust Fan
Fan Only

Bathroom Exhaust Fan
With Light

Bathroom Exhaust Fan
Fan with Humidistat

All of these Panasonic fans have 4” exhaust ports, backdraft dampers, and move 110 CFM (Cubic Feet per Minute) of air.  Do not install any fan that produces less than 110 CFM.  Do not let anyone install a 50 or 80 CFM fan.  They are cheaper but will not do the job!

Many Panasonic fans are UL Listed® for tub/shower enclosures when GFCI protected.  Panasonic fans provide superior moisture and odor control for improved indoor air quality and a healthier home.  They offer quiet yet powerful exhaust ventilation to help remove moist, unclean air.

A bathroom exhaust fan is for the health and safety of me and my family – right?

Mission Viejo Bathroom RemodelI could not have said it better myself!  This is precisely why California law requires a bathroom exhaust fan.  Consider for a moment the rashes, headaches, eye, nose, and throat irritation you have.  This could be resolved by better ventilating your bathrooms and eliminating the mold.  The cost likely pales in comparison to the doctors, medications and suffering you and your family may be experiencing.

Don’t forget that mold also destroys your home.  It eats away at anything containing wood or paper.  I’ve seen mold completely destroy a bathroom in 10 years.  I’ve also seen it move to other parts of the house.  Causing even more expensive damage.  If you do not have a bathroom exhaust fan and you are remodeling your bathroom, now is the time to do it.

Are there limitations on venting?

A bathroom exhaust fan can vent through the roof or the side of the house.  It cannot vent directly into attic space.  Exhaust fans must vent 3 feet or more away from a window.  If they vent through the side of the house, the exhaust must vent 3 feet or more away from the property line.

How Can I Receive More Information?

If you would like more information on enjoying the best bathroom, kitchen, and interior remodeling experience in Orange County, call Dan at (949) 380-0177 or at for a free in home consultation.  DAD’s serves all of South Orange County California.  This includes Lake Forest, Mission Viejo, Foothill Ranch, Portola Hills, Ladera Ranch, Irvine, San Clemente, Dana Point, San Juan Capistrano, Rancho Santa Margarita, Coto de Caza, Dove Canyon, Laguna Niguel, Laguna Hills, Newport Beach, and Aliso Viejo.

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Daniel A. Derkum is the owner of DAD’s Construction.  DAD’s is a leading South Orange County, California design-and-build remodeling and renovation Contractor.  See  © DAD’s Home Services & Construction, Inc.  All Rights Reserved.