Good home ventilation can protect your health and save you money at the doctor’s office. Poor ventilation can cause buildup of air pollutants and mold which can contribute to asthma and other respiratory problems. Poor ventilation can also cause humidity to build up causing mold and other home damage. To keep air quality optimal, pollutants must be exhausted, indoor air must be replaced by fresh outside air, and moisture must be controlled. AC filters need to be changed regularly—sometimes as often as once a month.