The risk of Covid-19 transmission indoors can be reduced by using fans in a strategic way. It is important to avoid placing fans in a way that could cause polluted air to flow directly from one person to another. A window fan, securely placed in a window, can be used to blow air out of the room to the outside. Portable fans, ceiling fans, and single-unit air conditioners usually circulate air inside a room, but they don't exchange air.
To minimize the risk of infection transmission, it is best to place a fan in front of an open window to increase airflow and blow indoor air out. Ceiling fans can also improve air circulation from the outside and prevent stagnant air pockets from forming inside. Ventilation with recirculated air will not reduce the risk of COVID-19 unless the recirculated air passes through a filter made to remove tiny particles. If it's not possible to create a cross breeze, you can place a fan in front of an open window to increase airflow and blow indoor air out.
Fans can face the window (blowing air out the window) or away from the window (blowing air into the room). Aircraft have cabin air filtration systems equipped with HEPA filters that can eliminate viruses and germs quickly, reducing the risk of exposure to any possible infectious virus or bacteria expelled by coughing or sneezing.
