Ventilation Information

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The virus that causes COVID-19 can spread from person to person through the air. The virus spreads more easily in indoor spaces where fresh air is not circulating.

You can reduce the risk of spreading COVID-19 in indoor spaces by ensuring fresh air is flowing in and out of rooms (ventilation) and by filtering air to make it cleaner to breathe.

When possible, avoid gathering with others in crowded indoor spaces that are not well ventilated. You can further reduce your risk of getting or spreading viruses indoors by appropriately wearing a high-quality mask, keeping extra space between yourself and others, and following other prevention steps.

Planning or attending gathering? Consult guidance to help keep your gathering safe.


Take steps to increase the flow of fresh air from outside into indoor spaces:

  • Open windows and doors and use fans to move fresh air through rooms.
  • When available, increase the amount of outdoor air that is pulled in through the heating, ventilation, and cooling (HVAC) system to 100%.
  • Open outdoor air dampers for the HVAC system to reduce the amount of air that is being recirculated through the building.


You can use air filtration systems to remove contaminants from indoor air and reduce the risk of spreading viruses.

  • Improve your existing HVAC system by having it evaluated by a specialist. Determine if it can handle high efficiency filters (rated MERV 13 or higher) and install those filters if it can. High efficiency filters will capture more contaminants in the air.
  • Use portable HEPA air cleaners that provide 99 percent or higher filtration efficiency down to 0.3 microns.
  • For a lower-cost option, use a box fan with a MERV 13 furnace filter attached to the back. Click here for instructions.
  • Ultraviolet Germicidal Irradiation (UVGI) systems can kill germs in the air but cannot remove pollutants. Use UVGI in addition to ventilation and air filtration to improve indoor air (this solution is only intended for specific spaces and not for inside homes).


Take additional steps to prevent the spread of COVID-19. This is especially important if you or someone close to you is at high risk for severe illness from COVID-19:

  • Stay up-to-date on COVID-19 vaccinations.
  • Wear a mask in indoor settings.
  • Maintain a space of at least 6 feet between people.
  • Avoid poorly ventilated indoor settings.
  • Test to prevent spread to others.
  • Wash your hands often, cover coughs and sneezes, clean and disinfect.

More Guidance:

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