Exhaust ventilation is probably the most common solution to meeting the continuous ventilation requirements. This is usually achieved by a quiet ceiling-mounted bath fan or remote mounted inline or exterior-mounted fans. Air is drawn from the house by the exhaust fan and outdoor air enters the house through leaks in the building envelope. Because the leaks are generally uniformly scattered throughout the house, outdoor air entering the house does not generally create drafty or uncomfortable conditions.
Many high quality bath fans are available in the 30 to 150 cfm size range and are quiet enough to be used continuously. One or more fans of this size will meet the requirements of most homes. The exhaust fan can be a dedicated indoor air quality fan or it can be a more typical bath fan that is used for both whole building ventilation and local ventilation. The fan shall be rated at a maximum of 1.0 sone.
Inline fans, either single pickup or multipoint pickup, can be a very effective method of providing quiet exhaust ventilation from one or several bathrooms. Inline fans can be located in the garage, attic, basement, or mechanical room. Exterior-mounted fans can be mounted on the exterior wall or on the roof. A sound rating is not required for remote or exterior fans as long as there is at least four feet of duct between the closest pickup grille and the fan.
(Excerpted from the CEC Title 24 Residential Compliance Manual)