What we do know is this: HVAC systems primarily recirculate air in a room or a building and don’t bring in any fresh air from outside. So yes, theoretically virus-containing aerosols could be sucked into an air conditioning system and then circulated around a building.

In one study, which is available online as a pre-print and has not undergone scientific review, researchers in Oregon collected samples from various places inside a hospital’s HVAC system and found genetic material from SARS-CoV-2, the virus that causes COVID-19. This demonstrates that it may be possible for the virus to be transmitted through HVAC systems.

However, researchers did not assess if the genetic material they found was able to cause infection, and they noted there were no confirmed COVID-19 cases associated with the samples found in the ventilation systems.

There is currently no other evidence documenting the possibility of COVID-19 transmission through an air conditioning unit.