Some Home Ventilation is Needed
If too little outdoor air enters a home, pollutants can sometimes accumulate to levels that can pose health and comfort problems. Outdoor air enters and leaves a structure by infiltration, natural ventilation, and mechanical ventilation.
In a process known as infiltration, outdoor air flows into the house through openings, joints, cracks in walls, floors, ceilings, and around windows and doors (air may also move out of the house in this manner - this is called exfiltration).
In natural ventilation, air moves through opened windows and doors. Air movement associated with infiltration and natural ventilation is caused by air temperature differences between indoors and outdoors and by wind. Mechanical ventilation may involve a number of ventilating devices, from a kitchen or bathroom exhaust fan to air handling systems that use fans and duct work to continuously remove indoor air and distribute filtered and conditioned outdoor air to strategic points throughout the facility. The rate at which outdoor air replaces indoor air is described as the air exchange rate. When there is little infiltration, natural ventilation or mechanical ventilation, the air exchange rate is low and pollutant levels can increase.