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Ventilation is the intentional exchange of indoor air with outdoor air to control indoor air quality, thermal comfort, and energy use. It removes stale air and pollutants while bringing in fresh air. Ventilation can occur naturally, through openings in the building envelope, or mechanically, using fans, ducts, and controlled airflows. Mixed-mode approaches combine both methods depending on conditions and occupancy.

Key concepts include the ventilation rate, typically measured as air changes per hour (ACH) or liters per second per person, and pollutant removal effectiveness. Systems may be exhaust ventilation, supply ventilation, or balanced ventilation. Some installations use heat or energy recovery to exchange heat and moisture between incoming and outgoing air, improving efficiency while maintaining indoor conditions. Filtration and humidity control are common design considerations in modern systems.

Standards and guidelines specify minimum outdoor air requirements by occupancy and activity, with examples such as ASHRAE Standard 62.1 and 62.2 in the United States, and EN 16798 in Europe. Design and maintenance practices address filtration quality, duct cleanliness, noise, and commissioning to ensure performance. Ventilation interacts with heating, cooling, and humidity control as part of overall indoor air quality management in homes, offices, schools, and healthcare facilities.

Note: The term "ventilationper..." appears to be incomplete; this article uses standard terminology for ventilation in general.