Step 2. Kitchen and Bath Ventilation

Meet Local Exhaust Ventilation Requirements in Kitchen and Bathrooms: Remove Pollutants at the Source

Local exhaust ventilation is installed near common sources of moisture and pollutants in a home (most commonly, kitchens and bathrooms). Fans must be certified to provide their rated airflow at 0.25 in w.c. (See the Home Ventilating Institute for airflow ratings of ventilation products certified by the Home Ventilating Institute). ASHRAE Standard 62.2 requires that local exhaust ventilation be provided for:

  • Kitchens: 100 cfm or more if intermittently operated OR 5 air changes per hour (ACH) of kitchen volume if continuously operated
  • Bathrooms: 50 cfm or more if operated intermittently OR 20 cfm if continuously operated

When the project budget is tight, a simple ventilation improvement such as an upgraded bath fan, though not ideal, can meet the minimum requirements for both local exhaust ventilation and whole-building ventilation.

Sound Ratings for Local Exhaust Fans

  • Certified maximum 3.0 sones for intermittently operated, local exhaust fans (The range hood must be a maximum of 3.0 sones when operated at its lowest speed).
  • Certified maximum 1.0 sones for continuously operated, local exhaust fans.
  • Inline and remote-mounted fans more than 4 feet from a ceiling grille have no sound requirements.
  • See the Home Ventilating Institute for sone ratings of ventilation products certified by the Home Ventilating Institute (HVI).

Custom Ventilation

In some situations, local exhaust equipment can be customized to the ventilation needs of occupants.

  • Ventilation requirements in laundry areas vary in different jurisdictions. The dryer fan usually exhausts 100-150 cfm while the dryer is in use. But in some households the laundry room houses multiple products that can cause health problems in sensitive people: bleach, cleaning products, dryer sheets, and other products with strong fumes. Locating the fan used for whole-building ventilation or a pick-up for the whole-building ventilation system in the laundry room could provide extra protection from household pollutants.
  • Hobby areas are not required by code to have local exhaust fans, but consider adding an exhaust fan to garage or basement work areas where occupants regularly use glues, paints, finishes, or similar products.

Note

Appendix A of ASHRAE 62.2-2010 offers an alternative calculation method for times when the kitchen and bath fans in an existing home are missing or inadequate and adding or replacing them is not possible. By increasing the flow of the whole-building ventilation equipment, local exhaust requirements can be met. This option is only available for existing homes – not in new construction. This method cannot be used to meet Title 24's local exhaust requirements.

Control Strategies for Local Exhaust Ventilation Fans

Local exhaust ventilation fans have a wide range of controls that will meet ASHRAE Standard 62.2. Most kitchen range hoods have built-in controls – usually simple on/off switch and speed settings. Bath fans have more control options. The goal is to pick a control that operates the fan for longer than the occupant is in the bathroom so that excess moisture can be removed. Some controls require occupants to turn on the fan. Some controls respond automatically to motion or humidity levels.

Ventilation Controls for Bath Fans and Range Hoods
Type Pros Cons
Fan/Light Switch None.

Not allowed by California Title 24. Fan and light must be switched separately.


Typically does not stay on long enough to remove moisture from bathroom.

Crank Timer Easy for occupant to set.

Older designs are noisy.


Must be set by occupant each time, so may not be used consistently.

Delay-Off Timer

Once set, operates automatically when switch is on.


When used, fan operates after occupant leaves the bathroom to remove more moisture.


May be wall switch or integrated into fan

Easy for occupant to defeat.


Occupant must operate switch each time, so may not be used consistently unless built into fan with other controls.

Humidity Sensor

Ensures fan operates after occupant leaves the bathroom to remove more moisture.


May be wall switch or integrated into fan.


Required for new construction for CalGreen Code.

Does not provide automatic exhaust unless triggered by shower or other high-humidity event.


Requires manual operation by occupant to address odors.


May be "fooled" by slow rise of humidity or seasonal changes in humidity, resulting in under-ventilation.

Occupancy Sensor

Automatically operates the fan whenever area is occupied.


Can be used to turn on exhaust fan or to shift multi-speed fan to high speed.


Some occupancy sensors incorporate a delay-off function as well.

May not "see" the whole room or when someone is in shower or stall.


Some controls can be triggered by animals or occupants passing in the hall.


Controls may turn off fan in room if occupant is not moving.

Continuous Fan Operation with Over-Ride

Continuous low-speed operation can meet requirement for both local exhaust ventilation and whole-building ventilation.


Some fans may include controls to boost to higher flow for local exhaust ventilation.


Ensures removal of moisture and other contaminants to decrease mold growth and improve indoor air quality.


Avoids problem of training occupants to operate equipment.

ASHRAE 62.2 requires a method of occupant over-ride for the whole-building ventilation system, so a labeled switch or control must be provided that can be accessed by the occupant.
Programmable Timer Can provide automatic operation for whole-building ventilation and manual controls for local exhaust ventilation. Programming the control is often complicated and difficult for installers and occupants to do reliably, resulting in over-ventilation or under-ventilation.