How big a room can one diffuser actually cover?

Small ultrasonic units (100–500ml) realistically scent a single room. Verified-purchase and community reviewers report that mid-size waterless units like the Airversa claim up to 2000 sq ft, while HVAC-integrated systems like the AROMADD target whole-home coverage. However, r/smarthome and r/UtahInfluencerDrama threads repeatedly warn that manufacturer square-footage claims are optimistic and that open floor plans need more output than expected.