Ventilation Can Reduce Exposure to Respiratory Viruses in Indoor Spaces

Summary

What CDC knows

Improving ventilation, whether natural or mechanical (air flow, filtration, and air treatment), reduces the number of small respiratory virus particles in indoor air, helping lower the risk of transmission. Ventilation is one of many tools available to help protect people from respiratory viruses.

What CDC is doing

CDC is providing actionable steps that people can take to reduce the number of small respiratory virus particles that circulate in indoor air. On March 1, 2024, CDC released updated guidance for respiratory viruses, which recommended taking steps for cleaner air, along with staying up to date on vaccines for respiratory illnesses such as COVID-19 and flu, as core prevention strategies to lower risk. Some of these recommended actions to improve ventilation may require systems-level changes, but individuals can still take steps to reduce exposure to virus particles in buildings, especially in their homes.

Ventilation can reduce respiratory virus transmission

By using core strategies, like vaccination and practicing good hygiene, we can protect ourselves and those we care about from respiratory illness. Improving ventilation is another one of the core strategies that can reduce our risk of catching or spreading respiratory viruses.

Good ventilation can help safeguard our health by reducing our exposure to respiratory viruses. People can still get sick after ventilating a space, so it is important to use ventilation as one part of a multi-layered approach to protect ourselves against getting sick from respiratory viruses.

It's important to take steps to improve ventilation in our homes and other indoor spaces as a core prevention strategy year round, from cold winters to hot summers.

How ventilation can help protect us

The risk of getting COVID-19 or other respiratory illnesses depends on several factors specific to the exposed person (like their immune system and vaccination status), the virus itself, and the environment in which the virus and the person interact. Improving ventilation can help protect people indoors. That's because viruses spread between people more easily indoors than outdoors in part because the concentration of these particles is often higher indoors.

Steps for cleaner air to prevent the spread of respiratory viruses can be taken any time, especially when:

• Respiratory viruses are causing a lot of illness in your community.
• You or the people around you were recently exposed to a respiratory virus, are sick, or are recovering.
• You or the people around you have risk factors for severe illness.

Ventilation can help keep indoor environments healthier

Respiratory viruses primarily spread in the air between people. The fewer viruses in the air, the better. Improving ventilation can help you reduce virus levels in your home and reduce the chances that the virus will spread.

We can improve indoor air quality by increasing airflow and cleaning the air. Making ventilation improvements in your home or building can increase the delivery of clean air and reduce the concentration of viruses in indoor spaces. Improved ventilation can be anything from easy actions such as opening windows to system upgrades.

Ventilation systems work in different ways: they can bring fresh, outdoor air into rooms, filter the air, or treat­ the air. They also serve to move air around, which reduces pockets of stagnant air where viral particles might accumulate.

Tips for year-round ventilation

There are many ways to improve the flow of air in our homes or other buildings:

• Bringing fresh, outdoor air indoors helps keep virus particles from accumulating in the indoor air. If it's safe to do so, open doors and windows as much as you can to bring in fresh outdoor air. Even having a window cracked open slightly can help.
• Make sure that your home heating, ventilation, and air conditioning (HVAC) systems operate as designed.
  • Maintain your system regularly as recommended by the manufacturer.
  • Change filters in your system regularly, according to the manufacturer's instructions.
  • Ensure filters fit properly in the filter rack, so as little air as possible gets around the filters.
• Aim to use multiple ventilation strategies in your home. This will help reduce the concentration of viral particles in the air.
• Use filters rated MERV-13 or higher, when possible. Using higher-rated filters in your heating or air conditioning system can remove more germs in the air than lower-rated filters.
• Set your ventilation system to circulate more air when people are in the building. You can do this by setting the thermostat's fan control to the "ON" position instead of "AUTO." This will make the fan operate continuously without having to adjust the temperature. This can increase fan energy use, so limit use to when needed, like shortly before, during, and after gathering of people or if someone in your home is sick with a respiratory virus.
• Air cleaners (also known as air purifiers) filter air with high-efficiency filters that remove germs from the air. Choose one that's the right size for your space.
• UV air treatment systems can kill germs in the air. They can also provide a high level of effective air changes per hour while using little energy.
• A portable CO₂ monitor can help you determine how stale or fresh the air is in rooms. Readings above 800 parts per million (ppm) suggest that you may need to bring more fresh, outdoor air into the space.
• Check that the exhaust fans in kitchens and bathrooms work and vent to outside your home or building. These fans help remove stale air and bring fresh air into your living spaces. You can also keep exhaust fans turned on when visitors are in your home and leave them on for an hour after they leave.
• If possible, move activities outdoors, to lower the risk of virus transmission.