Bringing fresh, outdoor air inside creates healthier indoor air.

After source control, the next step to improve air quality indoors is to ventilate with clean, outdoor air. Outdoor air has two to five times fewer pollutants than indoor air.

Like the lungs, homes and buildings need to be able to breathe. This ensures that fresh air comes in and dirty air goes out. Air indoors can build up high levels of moisture (humidity), odors, gases, dust and other air pollutants that can be harmful to health. To keep the air safe indoors, fresh outdoor air is needed to dilute these indoor pollutants and reduce humidity.

Ventilation helps reduce indoor air pollution, but it works best if paired with keeping known sources of air pollution out of the building. Ventilation alone is not a solution for high levels of indoor air pollution. For example, the only way to reduce the effect of secondhand smoke indoors is to not allow smoking indoors or near the entrances. Ventilation will not solve that problem.

Outdoor air can bring pollution indoors as well. If you live near a busy freeway, the diesel emissions from trucks can enter your home. If you live near a coal-burning factory, the outdoor may be polluted so taking steps to reduce outdoor air pollution is important, too.

Poor Ventilation Can Cause:

  • Build-up of airborne pollution, including: VOCs, particulate matter, carbon monoxide and other pollutants. 
  • High humidity levels which can cause mold and damage to the building, such as wood rot. 
  • Higher risk of infection from infectious diseases.

How Fresh Air Comes Indoors

Air comes into buildings and leaves by three different ways:

  • Infiltration occurs as a result of the building structure and design. Air can enter via chimneys, joints, cracks and openings where parts of the building connect, including floors and walls and around windows and pipes. Sometimes efforts to make buildings more energy efficient can backfire by not allowing enough air to move.
  • Natural ventilation provides air flow through natural forces. Opening up doors and windows provides natural ventilation.
  • Mechanical ventilation relies on fans and mechanical systems to move air.

Outdoor-vented fans in specific locations that produce high levels of pollutants or moisture, such as a bathroom or kitchen, help to draw out air from a small area – sometimes called “spot ventilation.” Many residential forced air-heating and air-conditioning systems do not bring outdoor air into the home, although newer, advanced systems offer a feature to bring in outdoor air.

Larger buildings, including multi-unit housing complexes and office buildings, may use whole building systems that continuously remove indoor air and replace it with filtered and conditioned outdoor air.

How to Use Ventilation to Protect Health

To provide good indoor air quality, enough air needs to be brought in and circulated so that it reaches all areas of the home or building.

How much ventilation is needed? Ventilation requirements vary for different types of buildings like medical facilities, office buildings, restaurants, and homes. The air exchange rate refers to how much and how quickly fresh, outdoor air replaces indoor air. The recommendation for residential buildings is to have at least .35 air changes of outdoor air for indoor hour per hour to maintain the quality of the indoor air. An HVAC technician can tell you your air exchange rate, or you can calculate your own using calculators found online.

Opening your doors and windows for 15 minutes each day is one of the best ways to increase ventilation. Opening multiple windows and doors can allow more fresh air to move inside. However, opening your doors and windows is not recommended on days with poor outdoor air quality, if you live close to busy highways, ports, airports, or factories with high emissions, or if there is wildfire smoke nearby. 

More ways to increase your ventilation and improve your indoor air quality include:

  • Use exhaust fans in bathrooms to remove moisture and gases from the house. Run fans while bathing and for 30-45 minutes afterward.
  • Fit your kitchen with an exhaust fan that moves the air outside. Use the fan or open a window when cooking to remove fumes, airborne particles, and moisture from cooking.
  • Use ceiling fans to improve air flow in the home, preferably with windows open.
  • If you paint or use hobby supplies or chemicals in your home, add extra ventilation. Open the windows and use a portable window fan to pull the air out of the room.
  • When indoor air pollution persists after controlling the source and increasing ventilation, air cleaning can help to filter the airborne pollutants from the air.

For More Information:

  • Ventilation in Buildings, the Centers for Disease Control and Prevention (CDC)
  • Heating, Ventilation and Air-Conditioning Systems, part of the Environmental Protection Agency’s “Indoor Air Quality Design Tools for Schools”
  • Indoor Air Quality Guide: Best Practices for Design, Construction and Commissioning, by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE)

Page last updated: November 14, 2023

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