A survey was conducted to determine occupant use of windows and mechanical ventilation devices; barriers that inhibit their use; satisfaction with indoor air quality (IAQ); and the relationship between these factors.A questionnaire was mailed to a stratified random sample of 4,972 single-family detached homes built in 2003, and 1,448 responses were received. A convenience sample of 230 houses known to have mechanical ventilation systems resulted in another 67 completed interviews.Results:- Many houses are under-ventilated: depending on season, only 10-50% of houses meet the standard recommendation of 0.35 air changes per hour. - Local exhaust fans are under-utilized. For instance, about 30% of households rarely or never use their bathroom fan. - More than 95% of households report that indoor air quality is "very" or "somewhat" acceptable," although about 1/3 of households also report dustiness, dry air, or stagnant or humid air. - Except households where people cook several hours per week, there is no evidence that households with significant indoor pollutant sources get more ventilation. - Except households containing asthmatics, there is no evidence that health issues motivate ventilation behavior.- Security and energy saving are the two main reasons people close windows or keep them closed.