Ventilation: How Buildings Breathe

Proper ventilation keeps the air fresh and healthy indoors.

Like the lungs, homes need to be able to breathe to make sure that fresh air comes in and dirty air goes out. Air indoors can build up high levels of moisture, odors, gases, dust, and other air pollutants. To keep the air safe indoors, fresh outdoor air is needed to dilute these indoor pollutants.

To provide good air quality, enough air needs to be brought in and circulated so that it reaches all areas of the home. For almost all homes, windows and structural elements contribute to bringing in fresh air. Many homes have additional mechanical systems to add to the flow. Some sources, such as stoves and bathrooms, need special venting that can remove the pollution they produce. Ventilation above stoves needs to carry the air outside to avoid redistributing pollutants from cooking inside the home.

Ventilation helps reduce indoor air pollution, but it works best if paired with keeping known sources of air pollution out of the building. 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 also bring pollution indoors as well, so taking steps to reduce outdoor air pollution is important, too.

How Fresh Air Comes into Your Home

Air comes into buildings and leaves by three different ways:

• Doors and windows, whenever they are opened.
• Joints, cracks and openings where parts of the building connect, including floors and walls and around windows and pipes.
• Spot ventilation, including fans that pull air from the bathroom.
• Mechanical, whole house systems, to systems in larger buildings that force air into and out of the building.

What Are Some Challenges Triggered by Poor Ventilation?

• When not enough air circulates, pollution builds up indoors. Sometimes efforts to make buildings more energy efficient can backfire by not allowing enough air to move, building up pollution.
• Carbon monoxide can build up to deadly levels indoors without proper ventilation, but it is not the only risk.
• Concentrations of radon, which can cause lung cancer, can increase in homes with low ventilation.
• High humidity outside can make indoor air more humid, increasing the risk of moisture damage indoors, such as mold growth or wood rot.

How to Use Ventilation to Protect Health

• Use exhaust fans in bathrooms to remove moisture and gases from the house.
• Fit your kitchen with an exhaust fan that moves the air to the outside. Use the fan or open a window when cooking to remove fumes and airborne particles.
• Make sure gas, propane, wood or other combustion appliances vent completely to the outside. Do not use ventless stoves. Install a carbon monoxide detector in multiple locations in your house.
• Vent clothes dryers to the outdoors, too. Clean out the vent regularly to make sure the dust does not block air flow.
• 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.
• Test your home for radon, and if you have elevated levels, hire a professional to add ventilation to remove it.  Radon is the second leading cause of lung cancer. 
• If the air indoors remains too moist, look for sources of moisture that need to be controlled. If that still does not solve the problem, if a dehumidifier may help.  If you use a dehumidifier, make certain you clean it regularly.  Check with an air systems specialist to see if your system needs improvements.
• Never idle your car in an attached garage. The exhaust can move into your home.

For more information:

An Introduction to Indoor Air Quality: Amount of Ventilation, U.S. Environmental Protection Agency.