Indoor Air Considerations: COVID-19
The information below is for general audiences who may have questions about air in buildings and COVID-19. Buildings with complex heating, ventilation, and air conditioning (HVAC) systems will typically need to work with HVAC professionals to evaluate and/or improve the ventilation, and health care facilities have their own ventilation standards. Note that the indoor air considerations in this document also apply to tents set up for events or businesses. Tents are defined as having two or more sides enclosed.
COVID-19 is spread mainly between people who are within about 6 feet of each other for at least 15 minutes. Tiny droplets form in the air when someone coughs, talks, sings, or laughs. Droplets from someone who has COVID-19 can contain the virus. Someone else can breathe in these droplets, or the droplets can land on someone’s eyes, nose, or mouth and cause infection. Indoors, there is less airflow to move around and spread out than there is outdoors.
Managing indoor air will not stop the spread of COVID-19 by itself, but it can lower the number of people infected when people also wear a face covering; stay at least 6 feet from others who are not household members; have good hand hygiene; clean and disinfect surfaces that are touched a lot; and take any other steps to control and stop infection.
Note: Things to consider about indoor air that are listed below may cost anywhere from nothing to thousands of dollars, and may take a little or a lot of work. They are only suggestions. They are not requirements. State agencies do not generally provide HVAC consultation or inspection. Be careful about using unproven technologies.
Air flow management
- Bring in fresh outdoor air as much as possible.
- Consider using rooms with high ceilings that have more space for anything in the air to move around and thin out.
- Limit the number of people in a space to a number that allows at least 50 square feet per person.
- Try to keep the indoor relative humidity between 40% and 60% in spring and fall. Consider lower levels of relative humidity in winter to stop too much moisture from forming on windows and other surfaces.
- Consider talking to an HVAC professional for help and more information.
Increase outdoor air ventilation
- Open windows and outer doors when weather and safety permits.
- Use a window air conditioner that has an outdoor air intake or vent with the vent open.
- The more people you have in an indoor area, the greater the need for outdoor air.
- Decrease the number of people in an area if outdoor ventilation cannot be increased.
Improve air circulation
- Open doors to rooms and hallways.
- Use restroom fans continuously in commercial or multifamily buildings, if possible.
- Use portable fans and ceiling fans with caution. The impact of fans on the risk of spreading the virus are unknown. They may help reduce risk, but must be positioned to avoid blowing air from one person in the direction of another person.
- Adjust ceiling fans to pull air up rather than down. For example, tilt blades upward, if possible.
- Place portable fans in windows to pull air out, rather than into the building.
- Standing or floor fans should be pointed away from people.
Filter indoor air
- Use a portable air cleaner or air purifier with a HEPA filter.
- Portable air cleaners can help reduce contaminants in the air, including viruses, in a home or confined space. Note that air cleaners/filters are not, by themselves, enough to protect people from the virus that causes COVID-19.
- Avoid ozone-producing air cleaners. See California Air Resources Board: Air Cleaners & Ozone Generating Products.
- Run the HVAC system fan for two hours before and after people are in a building or continuously, as HVAC systems filter 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.
- Upgrade the air filter in your HVAC system to a MERV 13 rating or as high as the system is capable (note that not all air filter manufacturers use MERV ratings, but they may have their own rating system).
- HVAC filters are designed to filter air throughout a home.
- Make sure filters are installed and fit correctly.
- Maintain and change filters regularly based on the manufacturer recommendations.
- Wear gloves and mask when changing the filter.
- Be aware that some portable and in-duct air cleaning devices can produce ozone, which could be harmful to health.
Evaluate ventilation and filtration performance
- In complex systems, such as commercial buildings or schools, evaluate ventilation and filters before making major changes and verify changes afterwards to confirm expected results (this is also called “commissioning” and “re-commissioning”).
- Work with an HVAC professional to evaluate building systems, ventilation, filtration, and air cleaning.
- Measure ventilation directly, when possible, such as air flow rates (outdoor air vs recirculated air) and pressure differences between higher risk areas (e.g., bathrooms, health office, band room) and other areas; carbon dioxide (CO2) can also be measured, to indirectly estimate ventilation rates, in high occupancy buildings.
- Coronavirus (COVID-19) Response Resources from ASHRAE and Others
Guidance on ventilation and filtration to help reduce risks from the virus that causes COVID-19.
- EPA: Indoor Air and Coronavirus (COVID-19)
- EPA: Guide to Air Cleaners in the Home (PDF)
- Harvard T.H. Chan School of Public Health: Schools for Health, Risk Reduction Strategies for Reopening Schools (PDF)
- Operating schools during COVID-19: CDC's Considerations