Ensuring proper ventilation with outside air can help reduce indoor airborne contaminants, including SARS-CoV-2, the virus that causes COVID-19, and other viruses. However, by itself, increasing ventilation is not enough to protect people from exposure to the virus that causes COVID-19. When used along with other best practices (such as wearing masks, social distancing, frequent hand washing, and surface disinfection) recommended by the CDC, increasing ventilation can be part of a plan to protect yourself and your family.

• Increase Ventilation with Outside Air
• Improving Natural Ventilation
• Use Your HVAC System and Consider Upgrading Filters
• Use a Portable Air Cleaner if You Have One
• Evaporative Coolers and Whole-House Fans

Increase Ventilation with Outside Air

• Open windows and screened doors. Do not open windows and doors if doing so poses a safety or health risk to children or other family members (e.g., risk of falling or triggering asthma symptoms).
• Operate a whole-house fan, or an evaporative cooler, if your home has one.
• Operate a window air conditioner that has an outdoor air intake or vent, with the vent open (some window air conditioners do not have outside air intakes).
• Open the outside air intake of the HVAC system, if yours has one (this is not common). Consult your HVAC manual or an HVAC professional for details.
• Operate a bathroom fan when the bathroom is in use and continuously, if possible.
• Operate the Heat Recovery Ventilator (HVR) or Energy Recovery Ventilator (ERV) if your home has one.

Caution: Avoid ventilation with outdoor air when outdoor air pollution is high or when it makes your home too cold, hot, or humid. Check AirNow for information about outdoor air pollution near you. In situations where wildfires are a concern, follow local advisories. Learn more about COVID-19, wildfires and indoor air quality.

For more information on increasing ventilation in homes, read residential guidance from ASHRAE. Exit

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Improving natural ventilation

Even with an open window or door, natural ventilation can be limited if inside and outside temperatures are similar and there is little wind.

• Open more than one window or door, if possible. Do not open windows and doors if doing so poses a safety or health risk to children or other family members (e.g., risk of falling or triggering asthma symptoms).
• Ventilation can be further increased through cross-ventilation, by opening windows (or doors) at opposite sides of a home and keeping internal doors open.
• Opening the highest and lowest windows in a home at the same time (especially on different floors) can also help to increase ventilation.
• For double-hung windows (the most common type), opening the top sash of one window and the bottom sash of another also encourages ventilation. Even when using a single window, partially opening both the top and bottom sash can help improve ventilation.

Consider using indoor fans in combination with open doors or windows to further increase ventilation. In addition to specialized window fans, box fans or tower fans can be placed in front of a window. Fans can face toward the window (blowing air out of the window) or away from the window (blowing air into the room).

• For additional ventilation, multiple fans can be used to push air out of one window and draw it in from another.
• If a single fan is used, it should be facing (and blowing air) in the same direction the air is naturally moving. You can determine the direction the air is naturally moving by observing the movement of drapes or by holding a light fabric or dropping paper clippings and noting which direction they move.
• The direction the air is blowing (in or out of the home) from a particular window or door may change at times, especially on windy days. If these changes are frequent, try moving the fan to another location. Also, you may not need to use a fan on windy days.
• To help reduce risks of airborne transmission, direct the airflow of the fan so that is does not blow directly from one person to another. 
• Caution: Use caution when operating fans, particularly when children are present. Position fans so they are out of reach of small children and so they are stable and won’t fall over easily. Consider using a tower or other fan where the blades are concealed or completely shielded.

For more information see information from the National Safety Council on window safety. Exit

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Use your HVAC system and consider upgrading filters

Since running your HVAC system filters the air as it is circulated, it can help reduce airborne contaminants, including viruses, indoors. By itself, running your HVAC system is not enough to protect yourself and your family from the virus that causes COVID-19. When used along with other best practices recommended by CDC, operating the HVAC system can be part of a plan to protect yourself and your family.

• Run the system fan for longer times, or continuously, as HVAC systems filter the air only when the fan is running. Many systems can be set to run the fan even when no heating or cooling is taking place.
• Check to be sure the filter is correctly in place and consider upgrading the filter to a higher efficiency filter or the highest-rated filter that your system fan and filter slot can accommodate. Consult your HVAC manual or an HVAC professional for details.
• Open the outside air intake, if your system has one (this is not common for home systems). Consult your HVAC manual or an HVAC professional for details.
• If your HVAC system has an energy-efficient air-to-air heat exchanger, heat recovery ventilator (HRV) or energy-recovery ventilator (ERV) use it, as they increase ventilation.

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Use a portable air cleaner or air purifier if you have one

When used properly, air purifiers can help reduce airborne contaminants, including viruses, in a home or confined space. However, by itself, a portable air cleaner is not enough to protect people from COVID-19. When used along with other best practices recommended by the CDC, operating an air cleaner can be part of a plan to protect yourself and your family. 

Place the air cleaner in the room you spend the most time in or where vulnerable people spend the most time. To help reduce risks of airborne transmission, direct the airflow of the air cleaner so that is does not blow directly from one person to another. For more information on who may be more vulnerable to COVID-19, refer to CDC's webpage about people at higher risk.

• Read EPA’s “Guide to air cleaners in the home” for information on placing and operating a portable air cleaner. 
• Visit the ASHRAE website for additional information. EXIT

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Evaporative coolers and whole-house fans

Evaporative coolers (or "swamp coolers") and whole-house fans can help protect people indoors from airborne transmission of COVID-19 because they increase ventilation with outside air to cool indoor spaces. However, by itself, an evaporative cooler or whole-house fan is not enough to protect people from COVID-19. When used along with other best practices recommended by the Centers for Disease Control and Prevention, operating an evaporative cooler or whole-house fan can be part of a plan to protect yourself and your family.

Evaporative coolers (sometimes referred to as swamp coolers) are used in dry climates. They use water to provide cooling and increase relative humidity indoors. They can be whole-house permanent systems, or less expensive portable units. When operating as intended (with open windows), these devices produce substantial increases in ventilation with outdoor air. Some evaporative coolers can be operated without using water when temperatures are milder, to increase ventilation indoors.

Avoid using evaporative coolers if air pollution outside is high and the system does not have a high-efficiency filter.

For additional information on selecting and using evaporative coolers, see the Department of Energy's evaporative coolers website.

Whole-house fans are typically used to provide cooling by pulling air through open windows and doors and exhausting it through the roof. When operated as intended, with open windows, these devices produce substantial increases in ventilation with outdoor air throughout a house. Avoid using whole-house fans if air pollution outside is high.

For additional information on selecting and using whole-house fans, see the Department of Energy's whole-house fans web page.

Return to Indoor Air and Coronavirus (COVID-19).