All houses and apartments need an efficient way to exhaust stale, moist indoor air and introduce outdoor air. Good ventilation makes a house healthier for occupants and protects the building structure from moisture damage.

A well-designed mechanical ventilation system with good controls is important to provide consistent ventilation through all seasons of the year for all housing. Fans exhaust stale air. Leaks, passive inlets, or another fan draws in outdoor air. Maintaining good indoor air quality in a house requires reducing pollution sources and providing adequate ventilation to remove and dilute pollutants.