Bathroom Ventilation

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Bathroom Ventilation

The most important part of your bathroom remodel is the bathroom ventilation.  Without a properly ventilated bathroom, you are inviting mold, mildew, bacteria, and a multitude of dangerous pathogens into your home.  You are also putting into motion the destruction of your remodeled bathroom before you even start.

What are the Signs I have a Bathroom Ventilation Problem?

All bathrooms invite moisture buildup.  A bathroom that has one or more of the below conditions is not properly ventilated:

Poor Bathroom VentilationMold in Bathroom from Poor Bathroom VentilationBathroom Ventilation Problem

If you have experienced any of the below moisture-related issues, it’s time to confront your bathroom’s ventilation problems before things get any worse.

  • Chipping or cracked paint
  • Peeling paint
  • Black or brown stains on the ceilings or walls
  • Gypsum (drywall) or plaster that is soft, peeling, disintegrating, or wet
  • Flooring that is soft, damaged, or wet
  • Peeling wallpaper
  • Delaminating (coming apart) crown molding or baseboards
  • Mold
  • Mildew
  • Humid air
  • Foul smells and odors
  • Moisture on wall surfaces

Bathroom Ventilation Has 3 Parts

A properly ventilated bathroom has all these items:

  • Exhaust fan
  • Window
  • HVAC
    Bathroom Exhaust Fan

Let’s explore each of these separately and see what part they play in bathroom ventilation.

Bathroom Exhaust Fan

The bathroom exhaust fan has 2 purposes.  These are removing odors and moisture.  In a water closet (separate toilet area behind a door) the primary purpose of the fan is to remove odors.  The purpose of the exhaust fan where the bathtub and/or shower is located (wet room) is to remove moisture.  The performance capacity of an exhaust fan is measured in the amount of air it removes per minute.  This measurement is called Cubic Feet per Minute (CFM).

What Size Bathroom Fan Do I Need?

Regardless of what you may read elsewhere, the exhaust fan needs to be rated at 110 CFM minimum.  Higher quality bathroom exhaust fans have a switch where you can adjust the CFM’s.  These typically allow for 50, 80, and 110 CFMs.  For larger bathrooms, there are fans that have an additional option for Bathroom Exhaust Fan150 CFMs.

In California, the California Residential Code (CRC) requires that bathroom exhaust fans in wet rooms be on a Humidistat.  These can be wall mounted or built into the fan.  The purpose of a Humidistat is to ensure when the level of moisture reaches a certain level (typically 50%), it automatically comes on and stays on until the moisture content of the bathroom area drops to 50%.

A bathroom exhaust fan must vent outside and be a minimum of 3 feet away from an opening or property line.

Where Is the Fan Installed?

The fan should be installed in the ceiling within 2 feet of the shower entrance.  If the bathroom has a tub/shower combination, the fan should be installed in the ceiling within 2 feet of the outside of the bathtub and centered on the tub apron or deck.  If your bathroom has both a shower and separate bathtub, the best location for the fan is in the ceiling within 2 feet of the shower entrance.

Do Bathroom Fans Need to be Automatic?

Bathroom fans do not need to come on automatically when you enter the room.  However, the CRC requires that they be on a humidistat or timer.  If the bathroom exhaust fan is in a room where there is a shower, tub/shower combination, or bathtub, the fan must be on a humidistat.  If the fan is in a separate water closet (where the toilet is located), it must be on a timer.

Humidistat for Exhaust Fan

Countdown Timer
Countdown Timer

A humidistat will turn the fan on and off automatically when the moisture level typically reaches 50%.  The fan can also be turned on and off manually.  However, if the level of moisture exceeds 50%, it will turn on automatically.

The timer ensures the fan does not stay on for hours or all day because you forgot to turn it off.  This is an energy saving function.  A typically 110cfm exhaust fan will do a complete air exchange in a home in 4 hours or less.  Think about how much electricity your air conditioner uses.  Can you imagine how expensive it would be if you had both the air conditioner and exhaust fan on together for hours?  All your nice cool air is being sucked out of the house by the fan!  The same is true for heat!

Bathroom Window

Most bathrooms already have at least one bathroom window.  In some homes, there is no window in the bathroom because it has no exterior wall.  When there is no exterior wall, a window is not usually possible.  The only other option when a window is not feasible is maybe a skylight.

Why is a Window Important for Bathroom Ventilation?

Bathroom WindowA bathroom window is your first choice for bathroom ventilation.  Typically, the window is directly over the shower or tub/shower.  When opened, it is the fastest way to remove moisture from the bathroom.  When another window in the house is open and the bathroom window is also open, it creates a chimney effect and rapidly removes moisture from the bathroom.

Why do I Need an Exhaust Fan if the Window Works so Good?

The California Residential Code (CRC) requires both a window and an exhaust fan in the bathroom.  Why?  The primary purpose of ventilating a bathroom is to remove moisture to stop mold, mildew, and bacteria from forming and damaging your bathroom, home, and your health.

Most people open the bathroom window in the warmer spring and summer months.  However, during the cold late fall and winter months, the bathroom window is closed.  People take much warmer/hotter showers for longer periods in colder months.  This dramatically increases moisture in the bathroom.  The exhaust fan now becomes the primary vehicle to remove moisture.  Moreover, when it is cold outside and warmer inside, condensation tends to increase in the bathroom.  Here again, with the window closed, the fan is the mechanism to remove the condensation and related moisture.

If your bathroom has a window, when practical, you should always open it for extra ventilation and the flow of fresh air.  An open window with the exhaust fan on will draw more air through the window.  The increased airflow will remove excess moisture faster than the running fan or open window alone.

Bathroom HVAC

The Heating, Ventilation, and Air Conditioning (HVAC) is the third part of your bathroom ventilation system.  The HVAC brings fresh air into your bathroom and removes moisture quickly.  It also does a great job of drying the bathroom out.  Knowing this, the logical question becomes “then why do I need a fan and window?”  Great question!  Most folks do not run their HVAC 24/7, 365 days a year.  The cost to do this would be outrages!  Few people run the air Bathroom HVAC conditioner when the outside temperature is 75 degrees or below.  In similar fashion, most people do not turn on the heater when the outside temperature is 60-65 degrees or higher.

Extreme temperatures are typically experienced only during the winter and summer months.  Virtually nobody has the bathroom window open when it’s freezing outside.  In similar fashion, hardly anybody will regularly think to turn on the bathroom fan when it’s freezing or hot outside.  This is when your HVAC becomes an important tool for removing moisture from your bathroom.  It also provides comfort during the hotter and colder months.  For the other 6 months of the year, the window and fan are the primary vehicles for removing moisture.

Always Hire a Reliable and Dependable Contractor to Remodel your Bathroom

Design Build Bathroom Remodel | Best Local Contractor DAD's ConstructionAlways work with a trustworthy contractor like DAD’s Construction.  We are experts in bathroom remodeling who can manage projects in an efficient manner.  DAD’s Construction will do everything to minimize the possibility of change orders.  Our team will make sure we have all the necessary information to prepare a proposal that meets your requirements.  Rest assured that we will provide you with a detailed, by line-item contract.  We will make sure that the contents of this agreement are properly and clearly communicated to you.  If you have questions or need updates regarding your project, we will always answer your inquiries.

How Can I Receive More Information on Remodeling my Bathroom?

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, Rancho 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, Laguna Beach, Newport Beach, and Aliso Viejo.

DAD’s Construction

“Taking Care of Your Home . . . The Way We Would Our Own”

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