A ceiling cassette is a mini-split indoor unit that mounts recessed into the ceiling, sitting flush so only its grille is visible. Four-way models are sized to drop into a standard 2-by-2-foot suspended-ceiling grid; one-way (single-flow) cassettes suit narrower spaces. Instead of pushing air from a wall, a cassette distributes it across the room — four-directional on most 4-way units, a full 360-degree pattern on round-flow designs — which gives even coverage in open rooms.
Cassettes are chosen when a wall head won't work or won't look right: open-plan living spaces, rooms with a drop ceiling or accessible plenum above, commercial-style interiors, or rooms where every wall is glass or furniture. Because the unit sits above the ceiling, the refrigerant line set and condensate drain are hidden entirely, leaving only a clean grille.
The practical considerations are the ceiling cavity and the condensate. A cassette needs sufficient depth above the finished ceiling to fit the body of the unit, so it's far easier in new construction or a drop-ceiling space than retrofitting a finished drywall ceiling. Because the unit is overhead, it relies on an integral condensate pump to lift water to a drain line rather than draining by gravity — a part to keep in mind for maintenance. Cassettes typically cost more than a comparable wall head, so the premium buys discretion and even airflow rather than performance.