Proper ventilation helps improve indoor air quality. Ventilation can control indoor humidity and airborne contaminants, both of which either contribute to or act as health hazards. The American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) and several states (Minnesota, Washington, and Vermont) have ventilation standards designed to ensure acceptable indoor air quality.

High indoor humidity can spur mold growth. High humidity may result from poor construction/rehabilitation, site design that does not properly manage water, and/or inadequate air exchange. A reasonable target for relative humidity is 30-60 percent. A low cost hygrometer, available at hardware stores, can be used to measure relative humidity. In cool climates, inadequate ventilation in the winter can contribute to excessive moisture and humidity because normal activities create moisture (cooking, bathing, breathing), and there is insufficient natural ventilation (opening windows) or mechanical ventilation (fans, exhaust systems) to remove the moisture. In warmer climates, the heating, ventilation, and air conditioning (HVAC) system can pull warmer, humid air inside. In this case, the ventilation system may help create indoor humidity problems unless the system also dehumidifies the air.

Common sources of airborne contaminants include:

Carbon monoxide (CO) is an odorless, colorless gas formed when carbon in fuels does not burn completely. Hundreds of Americans die every year from carbon monoxide poisoning caused by improperly used or malfunctioning fuel-burning appliances. Fetuses, young children, and the elderly are particularly susceptible to carbon monoxide poisoning.

Carbon monoxide is a “combustion pollutant”—a gas (or particle) that comes from burning carbon-based materials. Combustion pollutants are most often released into the home by vented or unvented appliances and vehicles running in an attached garage. Carbon monoxide is produced when there is a lack of oxygen or enough heat to burn fuels completely. The smoldering burn of incense or cigarettes also produces carbon monoxide.

Indoor Sources of Carbon Monoxide