The new guidance offers detailed recommendations for how to make indoor air healthier. Some of the strategies are as simple as opening a window to let in more outdoor air and using fans to increase the effectiveness of open windows.

In addition to better air circulation, the CDC recommends cleaning indoor air, using MERV-13 air filters in your HVAC system if possible. Air cleaners or purifiers may be helpful if they use high-efficiency particulate air (HEPA). The CDC says these are most important in high-risk areas like schools and medical offices. Systems that use UV light to kill germs may also be helpful.

As for how much ventilation is enough, the CDC suggests at least five air changes per hour to reduce germs.

CDC sets first target for indoor air ventilation to prevent spread of Covid-19

CDC Ventilation in Buildings